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  • 1.
    Abraham, Mark James
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Murtola, T.
    Schulz, R.
    Páll, Szilárd
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Smith, J. C.
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Gromacs: High performance molecular simulations through multi-level parallelism from laptops to supercomputers2015In: SoftwareX, ISSN 2352-7110, Vol. 1-2, p. 19-25Article in journal (Refereed)
    Abstract [en]

    GROMACS is one of the most widely used open-source and free software codes in chemistry, used primarily for dynamical simulations of biomolecules. It provides a rich set of calculation types, preparation and analysis tools. Several advanced techniques for free-energy calculations are supported. In version 5, it reaches new performance heights, through several new and enhanced parallelization algorithms. These work on every level; SIMD registers inside cores, multithreading, heterogeneous CPU-GPU acceleration, state-of-the-art 3D domain decomposition, and ensemble-level parallelization through built-in replica exchange and the separate Copernicus framework. The latest best-in-class compressed trajectory storage format is supported.

  • 2.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Mattle, Daniel
    Sitsel, Oleg
    Nielsen, Anna Marie
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    White, Stephen H.
    Nissen, Poul
    Gourdon, Pontus
    Transport Pathway in Cu+ P-Type ATPases2014In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, no 2, p. 427A-427AArticle in journal (Other academic)
  • 3.
    Apostolov, Rossen
    et al.
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Axner, Lilit
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Agren, Hans
    Ayugade, Eduard
    Duta, Mihai
    Gelpi, Jose Luis
    Gimenez, Judit
    Goni, Ramon
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Jamitzky, Ferdinand
    Kranzmuller, Dieter
    Labarta, Jesus
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Orozco, Modesto
    Peterson, Magnus
    Satzger, Helmut
    Trefethen, Anne
    Scalable Software Services for Life Science2011In: Proceedings of 9th HealthGrid conference, 2011Conference paper (Refereed)
    Abstract [en]

    Life Science is developing into one of the largest e- Infrastructure users in Europe, in part due to the ever-growing amount of biological data. Modern drug design typically includes both sequence bioinformatics, in silico virtual screening, and free energy calculations, e.g. of drug binding. This development will accelerate tremendously, and puts high demands on simulation software and support services. e-Infrastructure projects such as PRACE/DEISA have made important advances on hardware and scalability, but have largely been focused on theoretical scalability for large systems, while typical life science applications rather concern small-to-medium size molecules. Here, we propose to address this with by implementing new techniques for efficient small-system parallelization combined with throughput and ensemble computing to enable the life science community to exploit the largest next-generation e-Infrastructures. We will also build a new cross-disciplinary Competence Network for all of life science, to position Europe as the world-leading community for development and maintenance of this software e-Infrastructure. Specifically, we will (1) develop new hierarchical parallelization approaches explicitly based on ensemble and high-throughput computing for new multi-core and streaming/GPU architectures, and establish open software standards for data storage and exchange, (2) implement, document, and maintain such techniques in pilot European open-source codes such as the widely used GROMACS & DALTON, a new application for ensemble simulation (DISCRETE), and large-scale bioinformatics protein annotation, (3) create a Competence Centre for scalable life science software to strengthen Europe as a major software provider and to enable the community to exploit e-Infrastructures to their full extent. This Competence Network will provide training and support infrastructure, and establish a long-term framework for maintenance and optimization of life science codes.

  • 4. Bertaccini, E. J.
    et al.
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lindahl, Erik R.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Trudell, James Robert
    Department of Anesthesia, Stanford University School of Medicine, United States .
    Assessment of homology templates and an anesthetic binding site within the ?-aminobutyric acid receptor2013In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 119, no 5, p. 1087-1095Article in journal (Refereed)
    Abstract [en]

    Background: Anesthetics mediate portions of their activity via modulation of the ?-aminobutyric acid receptor (GABAaR). Although its molecular structure remains unknown, significant progress has been made toward understanding its interactions with anesthetics via molecular modeling. Methods: The structure of the torpedo acetylcholine receptor (nAChR?), the structures of the ?4 and ?2 subunits of the human nAChR, the structures of the eukaryotic glutamate-gated chloride channel (GluCl), and the prokaryotic pH-sensing channels, from Gloeobacter violaceus and Erwinia chrysanthemi, were aligned with the SAlign and 3DMA algorithms. A multiple sequence alignment from these structures and those of the GABAaR was performed with ClustalW. The Modeler and Rosetta algorithms independently created three-dimensional constructs of the GABAaR from the GluCl template. The CDocker algorithm docked a congeneric series of propofol derivatives into the binding pocket and scored calculated binding affinities for correlation with known GABAaR potentiation EC50s. Results: Multiple structure alignments of templates revealed a clear consensus of residue locations relevant to anesthetic effects except for torpedo nAChR. Within the GABAaR models generated from GluCl, the residues notable for modulating anesthetic action within transmembrane segments 1, 2, and 3 converged on the intersubunit interface between ? and ? subunits. Docking scores of a propofol derivative series into this binding site showed strong linear correlation with GABAaR potentiation EC50. Conclusion: Consensus structural alignment based on homologous templates revealed an intersubunit anesthetic binding cavity within the transmembrane domain of the GABAaR, which showed a correlation of ligand docking scores with experimentally measured GABAaR potentiation.

  • 5.
    Brömstrup, Torben
    et al.
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Howard, Rebecca J.
    Trudell, James R.
    Harris, R. Adron
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Inhibition versus Potentiation of Ligand-Gated Ion Channels Can Be Altered by a Single Mutation that Moves Ligands between Intra- and Intersubunit Sites2013In: Structure, ISSN 0969-2126, E-ISSN 1878-4186, Vol. 21, no 8, p. 1307-1316Article in journal (Refereed)
    Abstract [en]

    Pentameric ligand-gated ion channels (pLGICs) are similar in structure but either inhibited or potentiated by alcohols and anesthetics. This dual modulation has previously not been understood, but the determination of X-ray structures of prokaryotic GLIC provides an ideal model system. Here, we show that a single-site mutation at the F14' site in the GLIC transmembrane domain turns desflurane and chloroform from inhibitors to potentiators, and that this is explained by competing allosteric sites. The F14'A mutation opens an intersubunit site lined by N239 (15'), 1240 (16'), and Y263. Free energy calculations confirm this site is the preferred binding location for desflurane and chloroform in GLIC F14'A. In contrast, both anesthetics prefer an intrasubunit site in wild-type GLIC. Modulation is therefore the net effect of competitive binding between the intersubunit potentiating site and an intrasubunit inhibitory site. This provides direct evidence for a dual-site model of allosteric regulation of pLGICs.

  • 6.
    Brömstrup, Torben
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. Inst Pasteur, Grp Recepteurs Canaux, France.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Single-site mutation changes the location of the most favored Desflurane binding site in the GLIC ligand-gated ion channel2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 7. Conti, Luca
    et al.
    Renhorn, Jakob
    Gabrielsson, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Turesson, Fredrik
    Liin, Sara I.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. Stockholm University, Sweden.
    Elinder, Fredrik
    Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 27562Article in journal (Refereed)
    Abstract [en]

    Voltage-gated potassium channels open at depolarized membrane voltages. A prolonged depolarization causes a rearrangement of the selectivity filter which terminates the conduction of ions - a process called slow or C-type inactivation. How structural rearrangements in the voltage-sensor domain (VSD) cause alteration in the selectivity filter, and vice versa, are not fully understood. We show that pulling the pore domain of the Shaker potassium channel towards the VSD by a Cd2+ bridge accelerates C-type inactivation. Molecular dynamics simulations show that such pulling widens the selectivity filter and disrupts the K+ coordination, a hallmark for C-type inactivation. An engineered Cd2+ bridge within the VSD also affect C-type inactivation. Conversely, a pore domain mutation affects VSD gating-charge movement. Finally, C-type inactivation is caused by the concerted action of distant amino acid residues in the pore domain. All together, these data suggest a reciprocal communication between the pore domain and the VSD in the extracellular portion of the channel.

  • 8. Conti, Luca
    et al.
    Renhorn, Jakob
    Gabrielsson, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Turesson, Fredrik
    Liin, Sara
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Elinder, Fredrik
    A Reciprocal Voltage Sensor-To-Pore Coupling in C-Type Inactivation2016In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 110, no 3, p. 104A-104AArticle in journal (Other academic)
  • 9.
    Contreras, F.-Xabier
    et al.
    Heidelberg University.
    Ernst, Andreas M
    Heidelberg University.
    Haberkant, Per
    Heidelberg University.
    Björkholm, Patrik
    Stockholm University.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Gönen, Başak
    Tischer, Christian
    Heidelberg University.
    Elofsson, Arne
    Stockholm University.
    von Heijne, Gunnar
    Stockholm University.
    Thiele, Christoph
    Heidelberg University.
    Pepperkok, Rainer
    Heidelberg University.
    Wieland, Felix
    Heidelberg University.
    Brügger, Britta
    Heidelberg University.
    Molecular recognition of a single sphingolipid species by a protein's transmembrane domain2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 481, no 7382, p. 525-529Article in journal (Refereed)
    Abstract [en]

    Functioning and processing of membrane proteins critically depend on the way their transmembrane segments are embedded in the membrane. Sphingolipids are structural components of membranes and can also act as intracellular second messengers. Not much is known of sphingolipids binding to transmembrane domains (TMDs) of proteins within the hydrophobic bilayer, and how this could affect protein function. Here we show a direct and highly specific interaction of exclusively one sphingomyelin species, SM 18, with the TMD of the COPI machinery protein p24 (ref. 2). Strikingly, the interaction depends on both the headgroup and the backbone of the sphingolipid, and on a signature sequence (VXXTLXXIY) within the TMD. Molecular dynamics simulations show a close interaction of SM 18 with the TMD. We suggest a role of SM 18 in regulating the equilibrium between an inactive monomeric and an active oligomeric state of the p24 protein, which in turn regulates COPI-dependent transport. Bioinformatic analyses predict that the signature sequence represents a conserved sphingolipid-binding cavity in a variety of mammalian membrane proteins. Thus, in addition to a function as second messengers, sphingolipids can act as cofactors to regulate the function of transmembrane proteins. Our discovery of an unprecedented specificity of interaction of a TMD with an individual sphingolipid species adds to our understanding of why biological membranes are assembled from such a large variety of different lipids.

  • 10. Elber, R.
    et al.
    Ruymgaart, A. P.
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    SHAKE parallelization2011In: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 200, no 1, p. 211-223Article, review/survey (Refereed)
    Abstract [en]

    SHAKE is a widely used algorithm to impose general holonomic constraints during molecular simulations. By imposing constraints on stiff degrees of freedom that require integration with small time steps (without the constraints) we are able to calculate trajectories with time steps larger by approximately a factor of two. The larger time step makes it possible to run longer simulations. Another approach to extend the scope of Molecular Dynamics is parallelization. Parallelization speeds up the calculation of the forces between the atoms and makes it possible to compute longer trajectories with better statistics for thermodynamic and kinetic averages. A combination of SHAKE and parallelism is therefore highly desired. Unfortunately, the most widely used SHAKE algorithm (of bond relaxation) is inappropriate for parallelization and alternatives are needed. The alternatives must minimize communication, lead to good load balancing, and offer significantly better performance than the bond relaxation approach. The algorithm should also scale with the number of processors. We describe the theory behind different implementations of constrained dynamics on parallel systems, and their implementation on common architectures.

  • 11. Facey, Jody-Ann
    et al.
    Venner, Laura
    Hyde, Michael
    Pouya, Iman
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Howard, Rebecca
    Polar substitutions in the ion-conducting pore of GLIC alter gating and alcohol modulation2014In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 28, no 1, p. 1061.9-Article in journal (Other academic)
  • 12.
    Gabrielsson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Liin, Sara
    Elinder, Fredrik
    Lindahl, Erik
    Binding Structure & Dynamics for Toxins Modifying the Gating Mechanism of Kv Channels2014In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, no 2, p. 738A-738AArticle in journal (Other academic)
  • 13. Ganguly, Pritam
    et al.
    Schravendijk, Pim
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. Technische Universität Darmstadt, Germany; Stockholm University, Sweden .
    van der Vegt, Nico F. A.
    Ion Pairing in Aqueous Electrolyte Solutions with Biologically Relevant Anions2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 13, p. 3734-3739Article in journal (Refereed)
    Abstract [en]

    We performed molecular simulations to study ion pairing in aqueous solutions. Our results indicate that ion specific interactions of Li+, Na+, and K+ with the dimethyl phosphate anion are solvent-mediated. The same mechanism applies to carboxylate ions, as has been illustrated in earlier simulations of aqueous alkali acetate solutions. Contact ion pairs play only a minor role or no role at all in determining the solution structure and ion specific thermodynamics of these systems. On the basis of the Kirkwood Buff theory of solution we furthermore show that the well-known reversal of the Hofmeister series of salt activity coefficients, comparing chloride or bromide with dimethyl phosphate or acetate, is caused by changing from a contact pairing mechanism in the former system to a solvent-mediated interaction mechanism in the latter system.

  • 14. Hariharan, Parameswaran
    et al.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Jiang, Xiaoxu
    Pardon, Els
    Steyaert, Jan
    Kaback, H. Ronald
    Guan, Lan
    Thermodynamics of Nanobody Binding to Lactose Permease2016In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 55, no 42, p. 5917-5926Article in journal (Refereed)
    Abstract [en]

    Camelid nanobodies (Nbs) raised against the outward-facing conformer of a double-Trp mutant of the lactose permease of Escherichia coli (LacY) stabilize the permease in outward-facing conformations. Isothermal titration calorimetry is applied herein to dissect the binding thermodynamics of two Nbs, one that markedly improves access to the sugar-binding site and another that dramatically increases the affinity for galactoside. The findings presented here show that both enthalpy and entropy contribute favorably to binding of the Nbs to wild-type (WT) LacY and that binding of Nb to double-Trp mutant G46W/G262W is driven by a greater enthalpy at an entropic penalty. Thermodynamic analyses support the interpretation that WT LacY is stabilized in outward-facing conformations like the double-Trp mutant with closure of the cytoplasmic cavity through conformational selection. The LacY conformational transition required for ligand binding is reflected by a favorable entropy increase. Molecular dynamics simulations further suggest that the entropy increase likely stems from release of immobilized water molecules primarily from the cytoplasmic cavity upon closure.

  • 15. Henrion, Ulrike
    et al.
    Renhorn, Jakob
    Börjesson, Sara I.
    Nelson, Erin M.
    Schwaiger, Christine S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Bjelkmar, Pär
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Wallner, Björn
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Elinder, Fredrik
    Tracking a complete voltage-sensor cycle with metal-ion bridges2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 22, p. 8552-8557Article in journal (Refereed)
    Abstract [en]

    Voltage-gated ion channels open and close in response to changes in membrane potential, thereby enabling electrical signaling in excitable cells. The voltage sensitivity is conferred through four voltage-sensor domains (VSDs) where positively charged residues in the fourth transmembrane segment (S4) sense the potential. While an open state is known from the Kv1.2/2.1 X-ray structure, the conformational changes underlying voltage sensing have not been resolved. We present 20 additional interactions in one open and four different closed conformations based on metal-ion bridges between all four segments of the VSD in the voltage-gated Shaker K channel. A subset of the experimental constraints was used to generate Rosetta models of the conformations that were subjected to molecular simulation and tested against the remaining constraints. This achieves a detailed model of intermediate conformations during VSD gating. The results provide molecular insight into the transition, suggesting that S4 slides at least 12 angstrom along its axis to open the channel with a 3(10) helix region present that moves in sequence in S4 in order to occupy the same position in space opposite F290 from open through the three first closed states.

  • 16. Heusser, Stephanie A.
    et al.
    Howard, Rebecca J.
    Borghese, Cecilia M.
    Cullins, Madeline A.
    Brömstrup, Torben
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lee, Ui S.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Carlsson, Jens
    Harris, R. Adron
    Functional Validation of Virtual Screening for Novel Agents with General Anesthetic Action at Ligand-Gated Ion Channelss2013In: Molecular Pharmacology, ISSN 0026-895X, E-ISSN 1521-0111, Vol. 84, no 5, p. 670-678Article in journal (Refereed)
    Abstract [en]

    GABA(A) receptors play a crucial role in the actions of general anesthetics. The recently published crystal structure of the general anesthetic propofol bound to Gloeobacter violaceus ligand-gated ion channel (GLIC), a bacterial homolog of GABA(A) receptors, provided an opportunity to explore structure-based ligand discovery for pentameric ligand-gated ion channels (pLGICs). We used molecular docking of 153,000 commercially available compounds to identify molecules that interact with the propofol binding site in GLIC. In total, 29 compounds were selected for functional testing on recombinant GLIC, and 16 of these compounds modulated GLIC function. Active compounds were also tested on recombinant GABA(A) receptors, and point mutations around the presumed binding pocket were introduced into GLIC and GABA(A) receptors to test for binding specificity. The potency of active compounds was only weakly correlated with properties such as lipophilicity or molecular weight. One compound was found to mimic the actions of propofol on GLIC and GABA(A), and to be sensitive to mutations that reduce the action of propofol in both receptors. Mutant receptors also provided insight about the position of the binding sites and the relevance of the receptor's conformation for anesthetic actions. Overall, the findings support the feasibility of the use of virtual screening to discover allosteric modulators of pLGICs, and suggest that GLIC is a valid model system to identify novel GABA(A) receptor ligands.

  • 17. Heusser, Stephanie A.
    et al.
    Howard, Rebecca J.
    Pouya, Iman
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Klement, Göran
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Borghese, Cecilia
    Harris, R. Adron
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab. Stockholms universitet.
    A Single Mutation in GLIC Reveals Both the Potentiating and the Inhibitory Nature of Propofol2016In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 110, no 3, p. 456A-456AArticle in journal (Other academic)
  • 18. Heusser, Stephanie
    et al.
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Klement, Goran
    Reiderer, Erika
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Howard, Rebecca
    Functional Characterization of Neurotransmitter Activation and Modulation in a Nematode Model Ligand-gated Ion Channel2016In: Journal of Neurochemistry, ISSN 0022-3042, E-ISSN 1471-4159, Vol. 138, no 2, p. 243-253Article in journal (Refereed)
    Abstract [en]

    The superfamily of pentameric ligand-gated ion channels includes neurotransmitter receptors that mediate fast synaptic transmission in vertebrates, and are targets for drugs including alcohols, anesthetics, benzodiazepines and anticonvulsants. However, the mechanisms of ion channel opening, gating and modulation in these receptors leave many open questions, despite their pharmacological importance. Subtle conformational changes in both the extracellular and transmembrane domains are likely to influence channel opening, but have been difficult to characterize given the limited structural data available for human membrane proteins. Recent crystal structures of a modifiedCaenorhabditis elegans glutamate-gated chloride channel (GluCl) in multiple states offer an appealing model system for structure-function studies. However, the pharmacology of the crystallographic GluCl construct is not well established. To establish the functional relevance of this system, we used two-electrode voltage-clamp electrophysiology in Xenopus oocytes to characterize activation of crystallographic and native-like GluCl constructs by L-glutamate and ivermectin. We also tested modulation by ethanol and other anesthetic agents, and used site-directed mutagenesis to explore the role of a region of Loop F which was implicated in ligand gating by molecular dynamics simulations. Our findings indicate that the crystallographic construct functionally models concentration-dependent agonism and allosteric modulation of pharmacologically relevant receptors. Specific substitutions at residue Leu174 in loop F altered direct L-glutamate activation, consistent with computational evidence for this region's role in ligand binding. These insights demonstrate conservation of activation and modulation properties in this receptor family, and establish a framework for GluCl as a model system, including new possibilities for drug discovery.

  • 19. Howard, Rebecca J.
    et al.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Broemstrup, Torben
    Horani, Suzzane
    Lee, Ui S.
    Ondricek, Kathryn E.
    Corringer, Pierre-Jean
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Bertaccini, Edward J.
    Trudell, James R.
    Harris, R. Adron
    Combined functional-computational approach to characterize sites of anesthetic modulation of ligand-gated ion channels2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 20.
    Howard, Rebecca J
    et al.
    University of Texas.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Ondricek, Kathryn E
    University of Texas.
    Corringer, Pierre-Jean
    Institut Pasteur.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Trudell, James R
    Stanford University.
    Harris, R Adron
    University of Texas.
    Structural basis for alcohol modulation of a pentameric ligand-gated ion channel2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 29, p. 12149-54Article in journal (Refereed)
    Abstract [en]

    Despite its long history of use and abuse in human culture, the molecular basis for alcohol action in the brain is poorly understood. The recent determination of the atomic-scale structure of GLIC, a prokaryotic member of the pentameric ligand-gated ion channel (pLGIC) family, provides a unique opportunity to characterize the structural basis for modulation of these channels, many of which are alcohol targets in brain. We observed that GLIC recapitulates bimodal modulation by n-alcohols, similar to some eukaryotic pLGICs: methanol and ethanol weakly potentiated proton-activated currents in GLIC, whereas n-alcohols larger than ethanol inhibited them. Mapping of residues important to alcohol modulation of ionotropic receptors for glycine, γ-aminobutyric acid, and acetylcholine onto GLIC revealed their proximity to transmembrane cavities that may accommodate one or more alcohol molecules. Site-directed mutations in the pore-lining M2 helix allowed the identification of four residues that influence alcohol potentiation, with the direction of their effects reflecting α-helical structure. At one of the potentiation-enhancing residues, decreased side chain volume converted GLIC into a highly ethanol-sensitive channel, comparable to its eukaryotic relatives. Covalent labeling of M2 positions with an alcohol analog, a methanethiosulfonate reagent, further implicated residues at the extracellular end of the helix in alcohol binding. Molecular dynamics simulations elucidated the structural consequences of a potentiation-enhancing mutation and suggested a structural mechanism for alcohol potentiation via interaction with a transmembrane cavity previously termed the "linking tunnel." These results provide a unique structural model for independent potentiating and inhibitory interactions of n-alcohols with a pLGIC family member.

  • 21. Howard, Rebecca J.
    et al.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Ondricek, Kathryn E.
    Corringer, Pierre-Jean
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Trudell, James R.
    Harris, R. Adron
    Structural Basis For Alcohol Modulation of Pentameric Ligand-Gated Ion Channels2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 411A-411AArticle in journal (Other academic)
  • 22. Howard, Rebecca J.
    et al.
    Sauguet, Ludovic
    Brömstrup, Torben
    Swedish e-Science Resarch Centre.
    Murail, Samuel
    Lee, Ui S.
    Horani, Suzzane
    Trudell, James R.
    Corringer, Pierre-Jean
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Delarue, Marc
    Harris, R. Adron
    Alcohol and Anesthetic Binding to Pentameric Ligand-Gated Ion Channels Revealed in a Prokaryotic Model System2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 2, p. 635A-636AArticle in journal (Other academic)
  • 23.
    Johansson, Petter
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Carlson, Andreas
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Water-substrate physico-chemistry in wetting dynamics2015In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 781, p. 695-711Article in journal (Refereed)
    Abstract [en]

    We consider the wetting of water droplets on substrates with different chemical composition and molecular spacing, but with an identical equilibrium contact angle. A combined approach of large-scale molecular dynamics simulations and a continuum phase field model allows us to identify and quantify the influence of the microscopic physics at the contact line on the macroscopic droplet dynamics. We show that the substrate physico-chemistry, in particular hydrogen bonding, can significantly alter the flow. Since the material parameters are systematically derived from the atomistic simulations, our continuum model has only one adjustable parameter, which appears as a friction factor at the contact line. The continuum model approaches the atomistic wetting rate only when we adjust this contact line friction factor. However, the flow appears to he qualitatively different when comparing the atomistic and continuum models, highlighting that non-trivial continuum effects can come into play near the interface of the wetting front.

  • 24. Kasson, Peter M.
    et al.
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Probing microscopic material properties inside simulated membranes through spatially resolved three-dimensional local pressure fields and surface tensions2013In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 169, p. 106-112Article in journal (Refereed)
    Abstract [en]

    Cellular lipid membranes are spatially inhomogeneous soft materials. Materials properties such as pressure and surface tension thus show important microscopic-scale variation that is critical to many biological functions. We present a means to calculate pressure and surface tension in a 3D-resolved manner within molecular-dynamics simulations and show how such measurements can yield important insight. We also present the first corrections to local virial and pressure fields to account for the constraints typically used in lipid simulations that otherwise cause problems in highly oriented systems such as bilayers. Based on simulations of an asymmetric bacterial ion channel in a POPC bilayer, we demonstrate how 3D-resolved pressure can probe for both short-range and long-range effects from the protein on the membrane environment. We also show how surface tension is a sensitive metric for inter-leaflet equilibrium and can be used to detect even subtle imbalances between bilayer leaflets in a membrane-protein simulation. Since surface tension is known to modulate the function of many proteins, this effect is an important consideration for predictions of ion channel function. We outline a strategy by which our local pressure measurements, which we make available within a version of the GROMACS simulation package, may be used to design optimally equilibrated membrane-protein simulations.

  • 25.
    Kasson, Peter M.
    et al.
    University of Virginia, USA.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. Stockholm University, Sweden.
    Pande, Vijay S.
    Stanford University, United States .
    Water Ordering at Membrane Interfaces Controls Fusion Dynamics2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 11, p. 3812-3815Article in journal (Refereed)
    Abstract [en]

    Membrane interfaces are critical to many cellular functions, yet the vast array of molecular components involved make the fundamental physics of interaction difficult to define. Water has been shown to play an important role in the dynamics of small biological systems, for example when trapped in hydrophobic regions, but the molecular details of water have generally been thought dispensable when considering large membrane interfaces. Nevertheless, spectroscopic data indicate that water has distinct, ordered behavior near membrane surfaces. While coarse-grained simulations have achieved success recently in aiding understanding the dynamics of membrane assemblies, it is natural to ask, does the missing chemical nature of water play an important role? We have therefore performed atomic-resolution simulations of vesicle fusion to understand the role of chemical detail, particularly the molecular structure of water, in membrane fusion and at membrane interfaces more generally. These membrane interfaces present a form of hydrophilic confinement, yielding surprising, non-bulk-like water behavior.

  • 26. Kimanius, Dari
    et al.
    Forsberg, Bjorn O.
    Scheres, Sjors H. W.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Stockholm University, Sweden.
    Accelerated cryo-EM structure determination with parallelisation using GPUs in RELION-22016In: eLIFE, E-ISSN 2050-084X, Vol. 5, article id e18722Article in journal (Refereed)
    Abstract [en]

    By reaching near-atomic resolution for a wide range of specimens, single-particle cryo-EM structure determination is transforming structural biology. However, the necessary calculations come at large computational costs, which has introduced a bottleneck that is currently limiting throughput and the development of new methods. Here, we present an implementation of the RELION image processing software that uses graphics processors (GPUs) to address the most computationally intensive steps of its cryo-EM structure determination workflow. Both image classification and high-resolution refinement have been accelerated more than an order-of-magnitude, and template-based particle selection has been accelerated well over two orders-of-magnitude on desktop hardware. Memory requirements on GPUs have been reduced to fit widely available hardware, and we show that the use of single precision arithmetic does not adversely affect results. This enables high-resolution cryo-EM structure determination in a matter of days on a single workstation.

  • 27. Kimanius, Dari
    et al.
    Pettersson, Ingrid
    Schluckebier, Gerd
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab. Stockholm University, Sweden.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    SAXS-Guided Metadynamics2015In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 11, no 7, p. 3491-3498Article in journal (Refereed)
    Abstract [en]

    The small-angle X-ray scattering (SAXS) methodology enables structural characterization of biological macromolecules in solution. However, because SAXS provides low-dimensional information, several potential structural configurations can reproduce the experimental scattering profile, which severely complicates the structural refinement process. Here, we present a bias-exchange metadynamics refinement protocol that incorporates SAXS data as collective variables and therefore tags all possible configurations with their corresponding free energies, which allows identification of a unique structural solution. The method has been implemented in PLUMED and combined with the GROMACS simulation package, and as a proof of principle, we explore the Trp-cage protein folding landscape.

  • 28. Klement, Goran
    et al.
    Pouya, Iman
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Howard, Rebecca
    Lindahl, Erik
    Ligand-Gated Ion Channel Gating Kinetics and the Opening/Closing Mechanism are Sensitive to Mutations Altering the Hydrophobicity of the Ion Conduction Pore2014In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, no 2, p. 343A-343AArticle in journal (Other academic)
  • 29. Kutzner, C.
    et al.
    Apostolov, Rossen
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Grubmüller, H.
    Scaling of the GROMACS 4.6 molecular dynamics code on SuperMUC2014In: Advances in Parallel Computing, ISSN 0927-5452, E-ISSN 1879-808X, Vol. 25, p. 722-727Article in journal (Refereed)
    Abstract [en]

    Here we report on the performance of GROMACS 4.6 on the SuperMUC cluster at the Leibniz Rechenzentrum in Garching. We carried out benchmarks with three biomolecular systems consisting of eighty thousand to twelve million atoms in a strong scaling test each. The twelve million atom simulation system reached a performance of 49 nanoseconds per day on 32,768 cores.

  • 30. Kutzner, Carsten
    et al.
    Pall, Szilard
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Fechner, Martin
    Esztermann, Ansgar
    de Groot, Bert L.
    Grubmueller, Helmut
    Best bang for your buck: GPU nodes for GROMACS biomolecular simulations2015In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 36, no 26, p. 1990-2008Article in journal (Refereed)
    Abstract [en]

    The molecular dynamics simulation package GROMACS runs efficiently on a wide variety of hardware from commodity workstations to high performance computing clusters. Hardware features are well-exploited with a combination of single instruction multiple data, multithreading, and message passing interface (MPI)-based single program multiple data/multiple program multiple data parallelism while graphics processing units (GPUs) can be used as accelerators to compute interactions off-loaded from the CPU. Here, we evaluate which hardware produces trajectories with GROMACS 4.6 or 5.0 in the most economical way. We have assembled and benchmarked compute nodes with various CPU/GPU combinations to identify optimal compositions in terms of raw trajectory production rate, performance-to-price ratio, energy efficiency, and several other criteria. Although hardware prices are naturally subject to trends and fluctuations, general tendencies are clearly visible. Adding any type of GPU significantly boosts a node's simulation performance. For inexpensive consumer-class GPUs this improvement equally reflects in the performance-to-price ratio. Although memory issues in consumer-class GPUs could pass unnoticed as these cards do not support error checking and correction memory, unreliable GPUs can be sorted out with memory checking tools. Apart from the obvious determinants for cost-efficiency like hardware expenses and raw performance, the energy consumption of a node is a major cost factor. Over the typical hardware lifetime until replacement of a few years, the costs for electrical power and cooling can become larger than the costs of the hardware itself. Taking that into account, nodes with a well-balanced ratio of CPU and consumer-class GPU resources produce the maximum amount of GROMACS trajectory over their lifetime.

  • 31. Larsson, Per
    et al.
    Pouya, Iman
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    From Side Chains Rattling on Picoseconds to Ensemble Simulations of Protein Folding2014In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 54, no 8-9, p. 1274-1285Article, review/survey (Refereed)
    Abstract [en]

    Simulations of biological macromolecules have evolved tremendously since the discoveries of the 1970s. The field has moved from simple simulations in vacuo on picosecond scales to milliseconds of accurate sampling of large proteins, and it has become a standard tool in biochemistry and biophysics, rather than a dedicated theoretical one. This is partly due to increasing computational power, but it would not have been possible without huge research efforts invested in new algorithms and software. Here, we illustrate some of this development, both past and future challenges, and in particular, discuss how the recent introduction of modern ensemble methods is breaking the trend of ever-longer simulations to instead focus on throughput and sampling. This has not only helped simulations become much more accurate, but it provides statistical error estimates, which are critical, as simulations are increasingly used to predict properties that have not yet been measured experimentally.

  • 32. Laurent, Benoist
    et al.
    Murail, Samuel
    Brömstrup, Torben
    KTH.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Baaden, Marc
    Study of the Interaction between General Anesthetics and a Bacterial Homologue to the Human Nicotinic Receptor2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 2, p. 623A-623AArticle in journal (Other academic)
  • 33.
    Lindahl, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Edholm, Olle
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Solvent diffusion outside macromolecular surfaces1998In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 57, p. 791-796Article in journal (Refereed)
    Abstract [en]

    The effect of the inhomogeneous environment upon solvent molecules close to a macromolecular surface is evaluated from a molecular-dynamics simulation of a protein, myoglobin, in water solution. The simulation is analyzed in terms of a mean-field potential from the protein upon the water molecules and spatially varying translational diffusion coefficients for solvent molecules in directions parallel and perpendicular to the protein surface. The diffusion coefficients can be obtained from the slope of the average-square displacements vs time, as well as from the integral of the velocity autocorrelation functions. It is shown that the former procedure gives a lot of ambiguities due to the variation of the slope of the curve with time. The latter, however, after analytic correction for the contribution from algebraic long-time tails, furnish a much more reliable alternative.

  • 34.
    Lindahl, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Howard, R. J.
    Brömstrup, Torben
    KTH.
    Trudell, J. R.
    Bertaccini, E. J.
    The Molecular Mechanism For The Dual Alcohol Modulation Of Cys-Loop Receptors2012In: Alcoholism: Clinical and Experimental Research, ISSN 0145-6008, E-ISSN 1530-0277, Vol. 36, p. 74A-74AArticle in journal (Other academic)
  • 35.
    Lindahl, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Murail, Samuel
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Howard, Rebecca J.
    Brömstrup, Torben
    KTH, School of Biotechnology (BIO).
    Trudell, James
    Bertaccini, Edward J.
    The Molecular Mechanism for the Dual Alcohol Modulation of Cys-Loop Receptors2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 112A-112AArticle in journal (Other academic)
  • 36.
    Lindahl, Viveca
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Hess, Berk
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Accelerated weight histogram method for exploring free energy landscapes2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 4, p. 044110-Article in journal (Refereed)
    Abstract [en]

    Calculating free energies is an important and notoriously difficult task for molecular simulations. The rapid increase in computational power has made it possible to probe increasingly complex systems, yet extracting accurate free energies from these simulations remains a major challenge. Fully exploring the free energy landscape of, say, a biological macromolecule typically requires sampling large conformational changes and slow transitions. Often, the only feasible way to study such a system is to simulate it using an enhanced sampling method. The accelerated weight histogram (AWH) method is a new, efficient extended ensemble sampling technique which adaptively biases the simulation to promote exploration of the free energy landscape. The AWH method uses a probability weight histogram which allows for efficient free energy updates and results in an easy discretization procedure. A major advantage of the method is its general formulation, making it a powerful platform for developing further extensions and analyzing its relation to already existing methods. Here, we demonstrate its efficiency and general applicability by calculating the potential of mean force along a reaction coordinate for both a single dimension and multiple dimensions. We make use of a non-uniform, free energy dependent target distribution in reaction coordinate space so that computational efforts are not wasted on physically irrelevant regions. We present numerical results for molecular dynamics simulations of lithium acetate in solution and chignolin, a 10-residue long peptide that folds into a beta-hairpin. We further present practical guidelines for setting up and running an AWH simulation.

  • 37.
    Lundborg, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Apostolov, Rossen
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Spångberg, Daniel
    Gärdenäs, Anders
    van der Spoel, David
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    An Efficient and Extensible Format, Library, and API for Binary Trajectory Data from Molecular Simulations2014In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 35, no 3, p. 260-269Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations is an important application in theoretical chemistry, and with the large high-performance computing resources available today the programs also generate huge amounts of output data. In particular in life sciences, with complex biomolecules such as proteins, simulation projects regularly deal with several terabytes of data. Apart from the need for more cost-efficient storage, it is increasingly important to be able to archive data, secure the integrity against disk or file transfer errors, to provide rapid access, and facilitate exchange of data through open interfaces. There is already a whole range of different formats used, but few if any of them (including our previous ones) fulfill all these goals. To address these shortcomings, we present Trajectory Next Generation (TNG)a flexible but highly optimized and efficient file format designed with interoperability in mind. TNG both provides state-of-the-art multiframe compression as well as a container framework that will make it possible to extend it with new compression algorithms without modifications in programs using it. TNG will be the new file format in the next major release of the GROMACS package, but it has been implemented as a separate library and API with liberal licensing to enable wide adoption both in academic and commercial codes.

  • 38.
    Lundborg, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Center for Biomembrane Research, Stockholm University, Sweden .
    Automatic GROMACS Topology Generation and Comparisons of Force Fields for Solvation Free Energy Calculations2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 3, p. 810-823Article in journal (Refereed)
    Abstract [en]

    Free energy calculation has long been an important goal for molecular dynamics simulation and force field development, but historically it has been challenged by limited performance, accuracy, and creation of topologies for arbitrary small molecules. This has made it difficult to systematically compare different sets of parameters to improve existing force fields, but in the past few years several authors have developed increasingly automated procedures to generate parameters for force fields such as Amber, CHARMM, and OPLS. Here, we present a new framework that enables fully automated generation of GROMACS topologies for any of these force fields and an automated setup for parallel adaptive optimization of high-throughput free energy calculation by adjusting lambda point placement on the fly. As a small example of this automated pipeline, we have calculated solvation free energies of 50 different small molecules using the GAFF, OPLS-AA, and CGenFF force fields and four different water models, and by including the often neglected polarization costs, we show that the common charge models are somewhat underpolarized.

  • 39.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Broemstrup, Torben
    Howard, Rebecca
    Trudell, James
    Bertaccini, Edward J.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Molecular mechanism of the dual anesthetic modulation effect on Cys-loop receptors2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 40.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Howard, R. J.
    Broemstrup, Torben
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Bertaccini, E. J.
    Harris, R. A.
    Trudell, J. R.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Molecular Mechanism for the Dual Alcohol Modulation of Cys-loop Receptors2012In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 8, no 10, p. e1002710-Article in journal (Refereed)
    Abstract [en]

    Cys-loop receptors constitute a superfamily of pentameric ligand-gated ion channels (pLGICs), including receptors for acetylcholine, serotonin, glycine and γ-aminobutyric acid. Several bacterial homologues have been identified that are excellent models for understanding allosteric binding of alcohols and anesthetics in human Cys-loop receptors. Recently, we showed that a single point mutation on a prokaryotic homologue (GLIC) could transform it from a channel weakly potentiated by ethanol into a highly ethanol-sensitive channel. Here, we have employed molecular simulations to study ethanol binding to GLIC, and to elucidate the role of the ethanol-enhancing mutation in GLIC modulation. By performing 1-μs simulations with and without ethanol on wild-type and mutated GLIC, we observed spontaneous binding in both intra-subunit and inter-subunit transmembrane cavities. In contrast to the glycine receptor GlyR, in which we previously observed ethanol binding primarily in an inter-subunit cavity, ethanol primarily occupied an intra-subunit cavity in wild-type GLIC. However, the highly ethanol-sensitive GLIC mutation significantly enhanced ethanol binding in the inter-subunit cavity. These results demonstrate dramatic effects of the F(14′)A mutation on the distribution of ligands, and are consistent with a two-site model of pLGIC inhibition and potentiation.

  • 41.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Howard, Rebecca J.
    Trudell, James R.
    Bertaccini, Edward
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Tracing the Closing of a Ligand-Gated Ion Channel in Atomic Detail: An Unconstrained Four-Microsecond Simulation of GLIC Leads to a Closed State Remarkably Similar to ELIC2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 113A-114AArticle in journal (Other academic)
  • 42.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Wallner, Björn
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Trudell, James R.
    Bertaccini, Edward
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Microsecond Simulations Indicate that Ethanol Binds between Subunits and Could Stabilize an Open-State Model of a Glycine Receptor2011In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 100, no 7, p. 1642-1650Article in journal (Refereed)
    Abstract [en]

    Cys-loop receptors constitute a superfamily of ion channels gated by ligands such as acetylcholine, serotonin, glycine, and gamma-aminobutyric acid. All of these receptors are thought to share structural characteristics, but due to high sequence variation and limited structure availability, our knowledge about allosteric binding sites is still limited. These sites are frequent targets of anesthetic and alcohol molecules, and are of high pharmacological importance. We used molecular simulations to study ethanol binding and equilibrium exchange for the homomeric alpha 1 glycine receptor (GlyR alpha 1), modeled on the structure of the Gloeobacter violaceus pentameric ligand-gated channel. Ethanol has a well-known potentiating effect and can be used in high concentrations. By performing two microsecond-scale simulations of GlyR with/without ethanol, we were able to observe spontaneous binding in cavities and equilibrium ligand exchange. Of interest, it appears that there are ethanol-binding sites both between and within the GlyR transmembrane subunits, with the intersubunit site having the highest occupancy and slowest exchange (similar to 200 ns). This model site involves several residues that were previously identified via mutations as being crucial for potentiation. Finally, ethanol appears to stabilize the GlyR model built on a presumably open form of the ligand-gated channel. This stabilization could help explain the effects of allosteric ligand binding in Cys-loop receptors.

  • 43.
    Natarajan Arul, Murugan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Apostolov, Rossen Pavlov
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Kongsted, Jacob
    epartment of Physics, Chemistry and Pharmacy, University of Southern Denmark.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Association dynamics and linear and nonlinear optical properties of an N-acetylaladanamide probe in a POPC membrane2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 36, p. 13590-13597Article in journal (Refereed)
    Abstract [en]

    Along with the growing evidence that relates membrane abnormalities to various diseases, biological membranes have been acknowledged as targets for therapy. Any such abnormality in the membrane structure alters the membrane potential which in principle can be captured by measuring properties of specific optical probes. There exists by now many molecular probes with absorption and fluorescence properties that are sensitive to local membrane structure and to the membrane potential. To suggest new high-performance optical probes for membrane-potential imaging it is important to understand in detail the membrane-induced structural changes in the probe, the membrane association dynamics of the probe, and its membrane-specific optical properties. To contribute to this effort, we here study an optical probe, N-acetylaladanamide (NAAA), in the presence of a POPC lipid bilayer using a multiscale integrated approach to assess the probe structure, dynamics, and optical properties in its membrane-bound status and in water solvent. We find that the probe eventually assimilates into the membrane with a specific orientation where the hydrophobic part of the probe is buried inside the lipid bilayer, while the hydrophilic part is exposed to the water solvent. The computed absorption maximum is red-shifted when compared to the gas phase. The computations of the two-photon absorption and second harmonic generation cross sections of the NAAA probe in its membrane-bound state which is of its first kind in the literature suggest that this probe can be used for imaging the membrane potential using nonlinear optical microscopy.

  • 44. Nyblom, Maria
    et al.
    Poulsen, Hanne
    Gourdon, Pontus
    Reinhard, Linda
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fedosova, Natalya
    Nissen, Poul
    Crystal Structure of Na+, K+-ATPase in the Na+-Bound State2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 342, no 6154, p. 123-127Article in journal (Refereed)
    Abstract [en]

    The Na+, K+-adenosine triphosphatase (ATPase) maintains the electrochemical gradients of Na+ and K+ across the plasma membrane-a prerequisite for electrical excitability and secondary transport. Hitherto, structural information has been limited to K+-bound or ouabain-blocked forms. We present the crystal structure of a Na+-bound Na+, K+-ATPase as determined at 4.3 angstrom resolution. Compared with the K+-bound form, large conformational changes are observed in the a subunit whereas the beta and gamma subunit structures are maintained. The locations of the three Na+ sites are indicated with the unique site III at the recently suggested IIIb, as further supported by electrophysiological studies on leak currents. Extracellular release of the third Na+ from IIIb through IIIa, followed by exchange of Na+ for K+ at sites I and II, is suggested.

  • 45. Nys, Mieke
    et al.
    Farinha, Ana
    Wijckmans, Eveline
    Brams, Marijke
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Ulens, Chris
    The Crystal Structure of ELIC in Complex with Chlorpromazine Unexpectedly Unveils an Allosteric Binding Site in the Ligand-Binding Domain2016In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 110, no 3, p. 457A-457AArticle in journal (Other academic)
  • 46. Nys, Mieke
    et al.
    Wijckmans, Eveline
    Farinha, Ana
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Brams, Marijke
    Spurny, Radovan
    Peigneur, Steve
    Tytgat, Jan
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab. Stockholm University, Sweden.
    Ulens, Chris
    Allosteric binding site in a Cys-loop receptor ligand-binding domain unveiled in the crystal structure of ELIC in complex with chlorpromazine2016In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 113, no 43, p. E6696-E6703Article in journal (Refereed)
    Abstract [en]

    Pentameric ligand-gated ion channels or Cys-loop receptors are responsible for fast inhibitory or excitatory synaptic transmission. The antipsychotic compound chlorpromazine is a widely used tool to probe the ion channel pore of the nicotinic acetylcholine receptor, which is a prototypical Cys-loop receptor. In this study, we determine the molecular determinants of chlorpromazine binding in the Erwinia ligand-gated ion channel (ELIC). We report the X-ray crystal structures of ELIC in complex with chlorpromazine or its brominated derivative bromopromazine. Unexpectedly, we do not find a chlorpromazine molecule in the channel pore of ELIC, but behind the beta 8-beta 9 loop in the extracellular ligand-binding domain. The beta 8-beta 9 loop is localized downstream from the neurotransmitter binding site and plays an important role in coupling of ligand binding to channel opening. In combination with electrophysiological recordings from ELIC cysteine mutants and a thiol-reactive derivative of chlorpromazine, we demonstrate that chlorpromazine binding at the beta 8-beta 9 loop is responsible for receptor inhibition. We further use molecular-dynamics simulations to support the X-ray data and mutagenesis experiments. Together, these data unveil an allosteric binding site in the extracellular ligand-binding domain of ELIC. Our results extend on previous observations and further substantiate our understanding of a multisite model for allosteric modulation of Cys-loop receptors.

  • 47.
    Ollila, O H Samuli
    et al.
    Tampere University of Technology.
    Risselada, H Jelger
    University of Groningen.
    Louhivuori, Martti
    University of Groningen.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Vattulainen, Ilpo
    Tampere University of Technology,.
    Marrink, Siewert J
    University of Groningen.
    3D pressure field in lipid membranes and membrane-protein complexes2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 7, p. 078101-Article in journal (Refereed)
    Abstract [en]

    We calculate full 3D pressure fields for inhomogeneous nanoscale systems using molecular dynamics simulation data. The fields represent systems with increasing level of complexity, ranging from semivesicles and vesicles to membranes characterized by coexistence of two phases, including also a protein-membrane complex. We show that the 3D pressure field is distinctly different for curved and planar bilayers, the pressure field depends strongly on the phase of the membrane, and that an integral protein modulates the tension and elastic properties of the membrane.

  • 48. Olsen, Richard W.
    et al.
    Li, Guo-Dong
    Wallner, Martin
    Trudell, James R.
    Bertaccini, Edward J.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Miller, Keith W.
    Alkana, Ronald L.
    Davies, Daryl L.
    Structural Models of Ligand-Gated Ion Channels: Sites of Action for Anesthetics and Ethanol2014In: Alcoholism: Clinical and Experimental Research, ISSN 0145-6008, E-ISSN 1530-0277, Vol. 38, no 3, p. 595-603Article in journal (Refereed)
    Abstract [en]

    The molecular mechanism(s) of action of anesthetic, and especially, intoxicating doses of alcohol (ethanol [EtOH]) have been of interest even before the advent of the Research Society on Alcoholism. Recent physiological, genetic, and biochemical studies have pin-pointed molecular targets for anesthetics and EtOH in the brain as ligand-gated ion channel (LGIC) membrane proteins, especially the pentameric (5 subunit) Cys-loop superfamily of neurotransmitter receptors including nicotinic acetylcholine (nAChRs), GABA(A) (GABA(A)Rs), and glycine receptors (GlyRs). The ability to demonstrate molecular and structural elements of these proteins critical for the behavioral effects of these drugs on animals and humans provides convincing evidence for their role in the drugs' actions. Amino acid residues necessary for pharmacologically relevant allosteric modulation of LGIC function by anesthetics and EtOH have been identified in these channel proteins. Site-directed mutagenesis revealed potential allosteric modulatory sites in both the trans-membrane domain (TMD) and extracellular domain (ECD). Potential sites of action and binding have been deduced from homology modeling of other LGICs with structures known from crystallography and cryo-electron microscopy studies. Direct information about ligand binding in the TMD has been obtained by photoaffinity labeling, especially in GABA(A)Rs. Recent structural information from crystallized procaryotic (ELIC and GLIC) and eukaryotic (GluCl) LGICs allows refinement of the structural models including evaluation of possible sites of EtOH action.

  • 49. Orellana, Laura
    et al.
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Carrillo, Oliver
    Orozco, Modesto
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Prediction and Validation of Protein Intermediate States from Structurally Rich Ensembles and Coarse-Grained Simulations2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7Article in journal (Refereed)
    Abstract [en]

    Protein conformational changes are at the heart of cell functions, from signaling to ion transport. However, the transient nature of the intermediates along transition pathways hampers their experimental detection, making the underlying mechanisms elusive. Here, we retrieve dynamic information on the actual transition routes from Principal Component Analysis (PCA) of structurally-rich ensembles and, in combination with coarse-grained simulations, explore the conformational landscapes of five well-studied proteins. Modeling them as elastic networks in a hybrid Elastic-Network Brownian Dynamics simulation (eBDIMS), we generate trajectories connecting stable end-states that spontaneously sample the crystallographic motions, predicting the structures of known intermediates along thepaths. We also show that the explored non-linear routes can delimit the lowest energy passages between end-states sampled by atomistic molecular dynamics. The integrative methodology presented here provides a powerful framework to extract and expand dynamic pathway information from the Protein Data Bank, as well as to validate sampling methods in general. 

  • 50. Paulsen, Peter Aasted
    et al.
    Jurkowski, Wiktor
    Apostolov, Rossen
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Nissen, Poul
    Poulsen, Hanne
    The C-terminal cavity of the Na,K-ATPase analyzed by docking and electrophysiology2013In: Molecular membrane biology, ISSN 0968-7688, E-ISSN 1464-5203, Vol. 30, no 2, p. 195-205Article in journal (Refereed)
    Abstract [en]

    The Na,K-ATPase is essential to all animals, since it maintains the electrochemical gradients that energize the plasma membrane. Naturally occurring inhibitors of the pump from plants have been used pharmaceutically in cardiac treatment for centuries. The inhibitors block the pump by binding on its extracellular side and thereby locking it. To explore the possibilities for designing an alternative way of targeting the pump function, we have examined the structural requirements for binding to a pocket that accommodates the two C-terminal residues, YY, in the crystal structures of the pump. To cover the sample space of two residues, we first performed docking studies with the 400 possible dipeptides. For validation of the in silico predictions, pumps with 13 dipeptide sequences replacing the C-terminal YY were expressed in Xenopus laevis oocytes and examined with electrophysiology. Our data show a significant correlation between the docking scores from two different methods and the experimentally determined sodium affinities, which strengthens the previous hypothesis that sodium binding is coupled to docking of the C-terminus. From the dipeptides that dock the best and better than wild-type YY, it may therefore be possible to develop specific drugs targeting a previously unexplored binding pocket in the sodium pump.

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