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Localized Proton Microcircuits at the Biological Membrane-Water Interface
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.ORCID iD: 0000-0003-3200-0374
2006 (English)In: PNAS, ISSN 0027-8424, Vol. 103, no 52, 19677-19770 p.Article in journal (Refereed) Published
Abstract [en]

Cellular processes such as nerve conduction, energy metabolism, and import of nutrients into cells all depend on transport of ions across biological membranes through specialized membrane-spanning proteins. Understanding these processes at a molecular level requires mechanistic insights into the interaction between these proteins and the membrane itself. To explore the role of the membrane in ion translocation we used an approach based on fluorescence correlation spectroscopy. Specifically, we investigated exchange of protons between the water phase and the membrane surface, as well as diffusion of protons along membrane surfaces, at a single-molecule level. We show that the lipid head groups collectively act as a proton-collecting antenna, dramatically accelerating proton uptake from water to a membrane-anchored proton acceptor. Furthermore, the results show that proton transfer along the surface can be significantly faster than that between the lipid head groups and the surrounding water phase. Thus, ion translocation across membranes and between the different membrane protein components is a complex interplay between the proteins and the membrane itself, where the membrane acts as a proton-conducting link between membrane-spanning proton transporters

Place, publisher, year, edition, pages
2006. Vol. 103, no 52, 19677-19770 p.
Keyword [en]
diffusion; fluorescence; membrane protein; pH; proton transfer
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6539DOI: 10.1073/pnas.0605909103ISI: 000243285500030Scopus ID: 2-s2.0-33845936297OAI: oai:DiVA.org:kth-6539DiVA: diva2:11278
Note

QC 20100809

Available from: 2006-12-07 Created: 2006-12-07 Last updated: 2016-05-16Bibliographically approved
In thesis
1. Analysis of Fluorescence Flicker as a Tool to Monitor Proton Transport and Biomolecular Interactions
Open this publication in new window or tab >>Analysis of Fluorescence Flicker as a Tool to Monitor Proton Transport and Biomolecular Interactions
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The overall focus of this thesis is on fluorescence flicker processes of fluorescent molecules, e.g. protonation-deprotonation or singlet-triplet electronic state transitions, intrinsic or generated by their interaction with their environment, monitored by fluorescence spectroscopy.

Understanding proton migration along membranes and membrane proteins in cells is essential for understanding energy metabolism. It has been seen that certain membrane-spanning proton-transporter proteins in the respiratory chain in the mitochondrial inner membrane take up protons faster than the rate limited by diffusion. To explain these observations it has been suggested that there is a proton-collecting antenna, consisting of negatively and protonatable residues on the surface of these proteins, which increases the rate of uptake. Using fluorescence correlation spectroscopy and artificial biological membranes the proton collecting antenna effect is verified, as well as the proton migration properties on these membranes at various surface buffer concentrations.

Fluorescence flicker due to singlet-triplet electronic state transitions in a fluorescent molecule is interesting because of the long transition time between the two states. This means that the molecule has a long time to interact with the local environment, and can therefore be used as a microenvironmental sensor. A novel method for monitoring photo-induced, transient, long-lived, non- or weakly fluorescent states, e.g. the triplet state, was developed. With this method, only the time averaged intensity is detected and used for determining the triplet state kinetics. This method has several advantages, in particular it lends itself well for parallelization, over traditional methods including fluorescence correlation spectroscopy.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. iv, 30 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:75
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4216 (URN)978-91-7178-546-6 (ISBN)
Presentation
2006-12-20, FA31, Albanova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20101126Available from: 2006-12-07 Created: 2006-12-07 Last updated: 2010-11-26Bibliographically approved
2. Monitoring Proton Exchange and Triplet States with Fluorescence
Open this publication in new window or tab >>Monitoring Proton Exchange and Triplet States with Fluorescence
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fluorescent molecules commonly shift to transient dark states, induced bylight or triggered by chemical reactions. The transient dark states can beused as probes of the local environment surrounding the fluorescent molecules,and are therefore attractive for use in biomolecular applications. Thisthesis explores the use and development of novel fluorescence spectroscopictechniques for monitoring transient dark states.This work demonstrates that kinetic information regarding photoinduced transient dark states of fluorescent molecules can be obtained from the time-averaged fluorescence intensity of fluorescent molecules subject totemporally modulated illumination. Methods based on this approach havethe advantage that the light detectors can have a low time resolution, which allows for parallelization and screening of biomolecular interactions withhigh throughput. Transient state images are presented displaying local environmental differences such as those in oxygen concentration and quencher accessibility.Analysis of the fluorescence intensity fluctuations resulting from thetransitions to and from transient dark states can be used to obtain information regarding the transition rates and occupancy of the transient darkstates. Fluorescence fluctuation analysis was used to reveal rates of protonbinding and debinding to single fluorescent molecules located close to biological membranes and protein surfaces. The results from these studies show that the proton exchange rate increases dramatically when the fluorescent molecule is close to the membrane.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vii, 79 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:14
Keyword
fluorescence correlation spectroscopy, proton transfer, cytochrome c oxidase, transient state imaging, modulated excitation
National Category
Atom and Molecular Physics and Optics Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-10400 (URN)978-91-7415-304-0 (ISBN)
Public defence
2009-05-15, Sal FB42, AlbaNova, Roslagstullsbacken 21, Sstockholm, 09:00 (English)
Opponent
Supervisors
Note
QC 20100809Available from: 2009-05-13 Created: 2009-05-11 Last updated: 2011-01-24Bibliographically approved

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