Change search
Refine search result
1234 101 - 150 of 167
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Liu, Rong
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Högberg, Hans-Erik
    Mittuniversitetet.
    Preparation of the four stereoisomers of 3-bromo-2-butanol or their acetates via lipase-catalysed resolutions of the racemates derived from dl- or meso-2,3-butanediol.2005In: Tetrahedron: asymmetry, ISSN 0957-4166, E-ISSN 1362-511X, Vol. 16, p. 2607-2611Article in journal (Refereed)
    Abstract [en]

    The four stereoisomeric 3-bromo-2-butanols and/or their acetates were prepared via lipase-catalysed kinetic resolution by hydrolyses of the acetates of the (+/-)-syn- and (+/-)-anti-3-bromo-2-butanols, or via esterifications of the alc hols. The diastereomeric bromoacetates were obtained by syntheses from the dl- and meso-2,3-butanediols, respectively. On a preparative scale, the four stereoisomers, either as the free alcohols or as their acetates, were obtained in > 95% ee, and in 35-40% yield (based on the starting racemates).

  • 102.
    Lundgren, Stina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wingstrand, Erica
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hamberg, Anders
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Hult, Karl
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    ORGN 402-Dual activation in enantioselective synthesis of cyanohydrins2006In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 232Article in journal (Other academic)
  • 103.
    Léonard, Valérie
    et al.
    Univ Rochelle, FRE CNRS 2766, Lab Biotechnol & Chim Bioorgan.
    Fransson, Linda
    KTH, School of Biotechnology (BIO), Biochemistry.
    Lamare, Sylvain
    Univ Rochelle, FRE CNRS 2766, Lab Biotechnol & Chim Bioorgan.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Graber, Marianne
    Univ Rochelle, FRE CNRS 2766, Lab Biotechnol & Chim Bioorgan.
    A water molecule in the stereospecificity pocket of Candida antarctica lipase B enhances enantioselectivity towards pentan-2-ol2007In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 8, no 6, p. 662-667Article in journal (Refereed)
    Abstract [en]

    The effect of water activity on enzyme-catalyzed enantioselective transesterification was studied by using a solid/gas reactor. The experimental results were compared with predictions from molecular modelling. The system studied was the esterification of pentan-2-ol with methylpropanoate as acyl donor and lipase B from Candida antarctica as catalyst. The data showed a pronounced water-activity effect on both reaction rote and enantioselectivity. The enantioselectivity increased from 100, at water activity close to zero, to a maximum of 320, at a water activity of 0.2. Molecular modelling revealed how a water molecule could bind in the active site and obstruct the binding of the slowly reacting enantiomer. Measurements of enantioselectivity at different water-activity values and temperatures showed that the water molecule had a high affinity for the stereospecificity pocket of the active site with a binding energy of 9 kJ mol(-1), and that it lost all its degrees of rotation, corresponding to an entropic energy of 37 Jmol(-1)K(-1).

  • 104.
    Magnusson, Anders O.
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Takwa, Mohamad
    KTH, School of Biotechnology (BIO), Biochemistry.
    Harnberg, Anders
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    An S-selective lipase was created by rational redesign and the enantioselectivity increased with temperature2005In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 44, no 29, p. 4582-4585Article in journal (Refereed)
    Abstract [en]

    Higher activity with larger pockets: The figure shows a superposition of intermediates that occur in acyl transfer to (S)-1-phenylethanol catalyzed by Candida antarctica lipase B (CALB). Wild-type CALB cannot accomodate the phenyl group (gray) in the stereospecificity pocket and form all of the catalytically essential H bonds. The Trp 104 Ala mutation liberates the volume in yellow, the S enantiomer is easily fitted, and the specificity constant increases by a factor of 130 000.

  • 105.
    Martinelle, M
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Holmquist, M
    Clausen, I G
    Patkar, S
    Svendsen, A
    Hult, K
    The role of Glu87 and Trp89 in the lid of Humicola lanuginosa lipase1996In: Protein Engineering, ISSN 0269-2139, E-ISSN 1460-213X, Vol. 9, no 6, p. 519-524Article in journal (Refereed)
    Abstract [en]

    The importance of Glu87 and TRp89 in the lid of Humicola lanuginosa lipase for the hydrolytic activity at the water/lipid interface was investigated by site-directed mutagenesis. It was found that the effect on the hydrolytic activity upon the replacement of Trp89 with Phe, Leu, Gly or Glu was substrate dependent, The Trp89 mutants displayed an altered chain length specificity towards triglycerides, with a higher relative activity towards triacetin and trioctanoin compared with tributyrin, Trp89 was shown to be less important in the hydrolysis of vinyl esters compared with ethyl esters and triglycerides. An exclusive effect on the acylation reaction rate by the mutation of Trp89 was consistent with the data, It is suggested that Trp89 is important in the process of binding the acyl chain of the substrate into the active site for optimal acylation reaction rate, The Trp89Phe mutation resulted in an increased hydrolytic activity towards 2-alkylalkanoic acid esters. This is suggested to be due to reduction of unfavourable van der Waals contacts between Trp89 and the 2-substituent of the substrate, Thus, in contrast to natural substrates, Trp89 has a negative impact on the catalytic efficiency when substrates with bulky acyl chains are used, In contrast to the Trp89 mutations, the effect on the hydrolytic activity of the Glu87Ala mutation was almost substrate independent, 35-70% activity of wild-type lipase, A reduction of both the acylation and deacylation reaction was consistent with the data.

  • 106.
    MARTINELLE, M
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    HOLMQUIST, M
    HULT, K
    ON THE INTERFACIAL ACTIVATION OF CANDIDA-ANTARCTICA LIPASE-A AND LIPASE-B AS COMPARED WITH HUMICOLA-LANUGINOSA LIPASE1995In: BIOCHIMICA ET BIOPHYSICA ACTA-LIPIDS AND LIPID METABOLISM, ISSN 0005-2760, Vol. 1258, no 3, p. 272-276Article in journal (Refereed)
    Abstract [en]

    The interfacial activation of Candida antarctica lipase A (CALA) and B (CALB) has been investigated and compared with that of Humicola lanuginosa lipase (HLL). CALB displayed no interfacial activation towards p-nitrophenyl butyrate (PNPB) when exceeding the solubility limit of the substrate. No activation was observed towards p-nitrophenyl acetate (PNPA) at the addition of sodium dodecyl sulfate (SDS) nor in the presence of a solid polystyrene surface. The catalytic action of CALB was very different from that of Humicola lanuginosa lipase, which showed a pronounced interfacial activation with the same substrates. The basis for the anomalous behaviour of CALB is proposed to be due to the absence of a lid that regulates the access to the active site. in contrast to CALB, CALA expressed interfacial activation, but the activation was not as prominent as for Humicola lanuginosa lipase (HLL). The structural basis for the activation of CALA is unknown.

  • 107.
    MARTINELLE, M
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    HULT, K
    KINETICS OF ACYL TRANSFER-REACTIONS IN ORGANIC MEDIA CATALYZED BY CANDIDA-ANTARCTICA LIPASE-B1995In: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology, ISSN 0167-4838, E-ISSN 1879-2588, Vol. 1251, no 2, p. 191-197Article in journal (Refereed)
    Abstract [en]

    The acyl transfer reactions catalysed by Candida antarctica lipase B in organic media followed a bi-bi ping-pong mechanism, with competitive substrate inhibition by the alcohols used as acyl accepters. The effect of organic solvents on V-m and K-m was investigated. The V-m values in acetonitrile was 40-50% of those in heptane. High K-m values in acetonitrile compared to those in heptane could partly be explained by an increased solvation of the substrates in acetonitrile. Substrate solvation caused a 10-fold change in substrate going from heptane to acetonitrile. Deacylation was the rate determining specificity, defined as (V-m/K-m)(ethyl) (octanoate)/(V-m/K-m)(octanoic) (acid), step for the acyl transfer in heptane with vinyl- and ethyl octanoate as acyl donors and (R)-2-octanol as acyl acceptor. With I-octanol, a rate determining deacylation step in heptane was indicated using the same acyl donors. Using I-octanol as acceptor in heptane, S-ethyl thiooctanoate had a 25- to 30-fold lower V-m/K-m value and vinyl octanoate a 4-fold higher V-m/K-m value than that for ethyl octanoate. The difference showed to be a K-m effect for vinyl octanoate and mainly a K-m effect for S-ethyl thiooctanoate. The V-m values of the esterification of octanoic acid with different alcohols was 10-30-times lower than those for the corresponding transesterification of ethyl octanoate. The low activity could be explained by a low pH around the enzyme caused by the acid or a withdrawing of active enzyme by nonproductive binding by the acid.

  • 108. Marton, Z.
    et al.
    Leonard-Nevers, V.
    Syrén, Per-Olof
    KTH, School of Biotechnology (BIO), Biochemistry.
    Bauer, C.
    Lamare, S.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Tranc, V.
    Graber, M.
    Mutations in the stereospecificity pocket and at the entrance of the active site of Candida antarctica lipase B enhancing enzyme enantioselectivity2010In: Journal of Molecular Catalysis B: Enzymatic, ISSN 1381-1177, E-ISSN 1873-3158, Vol. 65, no 1-4, p. 11-17Article in journal (Refereed)
    Abstract [en]

    Two different parts of Candida antarctica lipase B (stereospecificity pocket at the bottom of the active site and hydrophobic tunnel leading to the active site) were redesigned by single- or double-point mutations, in order to better control and improve enzyme enantioselectivity toward secondary alcohols. Single-point isosteric mutations of Ser47 and Thr42 situated in the stereospecificity pocket gave rise to variants with doubled enantioselectivity toward pentan-2-ol, in solid/gas reactor. Besides, the width and shape of the hydrophobic tunnel leading to the active site was modified by producing the following single-point mutants: Ile189Ala, Leu278Val and Ala282Leu. For each of these variants a significant modification of enantioselectivity was observed compared to wild-type enzyme, indicating that discrimination of the enantiomers by the enzyme could also arise from their different accessibilities from the enzyme surface to the catalytic site. (C) 2010 Elsevier B.V. All rights reserved.

  • 109. Marzorati, Mattia
    et al.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Riva, Sergio
    Danieli, Bruno
    Incorporation of primary amines into a polyester chain by a combination of chemical and lipase-catalyzed epsilon-caprolactone ring-opening processes2007In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 349, no 12-nov, p. 1963-1968Article in journal (Refereed)
    Abstract [en]

    A simple chemoenzymatic strategy for the incorporation of bioactive and suitably functionalized molecules into a polyester chain has been developed. The protocol involves first the reaction of a primary amine with E-caprolactone to give an amide carrying a terminal primary hydroxy group, followed by the enzymatic growth of the polymeric chain triggered by Novozym 435. This method is versatile and of different amines into polyesters, as has been shown with the model compounds benzylamine and tryptamine, the bioactive compound N-deacetylthiocolchicine and the functionalized propargylamine and tyramine.

  • 110.
    Moberg, Christina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wingstrand, Erica
    Lundgren, Stina
    Hamberg, Anders
    Penhoat, Mael
    Engstrom, Kann
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    ORGN 512-Asymmetric cyano-acylation of aldehydes: Use of a new high throughput screen for readout of conversion and ee2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 236, p. 512-ORGNArticle in journal (Refereed)
  • 111. Naik, Sangeeta
    et al.
    Basu, Aditya
    Saikia, Rakhi
    Madan, Bhawna
    Paul, Pritish
    Chaterjee, Robin
    KTH, School of Biotechnology (BIO), Biochemistry.
    Brask, Jesper
    Svendsen, Allan
    Lipases for use in industrial biocatalysis: Specificity of selected structural groups of lipases2010In: Journal of Molecular Catalysis B: Enzymatic, ISSN 1381-1177, E-ISSN 1873-3158, Vol. 65, no 1-4, p. 18-23Article in journal (Refereed)
    Abstract [en]

    Lipases for biocatalysis The substrate specificity of a selected group of lipases was investigated. The enzymes selected were from four structural groups. Group 1: lipases having wide alcohol binding cleft but a narrow acyl binding cleft (Rhizomucor miehei lipase. Thermomyces lanuginosus lipase. Fusarium oxysporum lipase); Group 2: lipases which exhibit strong restriction on the acid part having a narrow tunnel to accommodate the acyl group but wider alcohol binding site (Candida antarctica A, Candida rugosa lipase); Group 3: lipases having wide acyl binding cleft but narrow alcohol binding cleft (C. antarctica lipase B, Ustilago maydis lipase), and Group 4: having wider alcohol and wider acyl binding clefts (Fusarium solani pisi cutinase, Humicola insolens cutinase). Owing to the wide substrate specificity and higher expression levels in recombinant host, these lipases have tremendous importance for hydrolysis and synthesis reactions. Various substrates with substitutions on the alcohol and/or the acid part of the ester molecule were selected. The experimental results support the classification of lipases on the basis of their binding sites. For substrates with heavy alcohol side, C. Antarctica lipase A and R. miehei lipase type enzymes gave the highest extent of hydrolysis, while for acid heavy substrates the highest conversions were shown by C. antarctica lipase B. It is noteworthy that the acid heavy substrates which had aromatic side chains were hydrolyzed only by C. antarctica lipase B type of enzymes. Lipases were found to be more active on the alcohol-substituted substrates than acid-substituted substrates. (C) 2010 Elsevier B.V. All rights reserved.

  • 112. Neubauer, A.
    et al.
    Golson, R.
    Ukkonen, K.
    Krause, M.
    Tegel, Hanna
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Ottosson, Jenny
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Wittrup Larsen, Marianne
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Neubauer, P.
    Vasala, A.
    Controlling nutrient release in cell cultivation2009In: Genetic Engineering and Biotechnology News, ISSN 1935-472X, Vol. 29, no 11, p. 50-51Article in journal (Refereed)
  • 113.
    Nyrén, Pål
    KTH, School of Biotechnology (BIO), Biochemistry.
    The history of pyrosequencin2007In: Vol. 373, p. 1-14Article in journal (Refereed)
    Abstract [en]

    One late afternoon in the beginning of January 1986, bicycling from the lab over the hill to the small village of Fullbourn, the idea for an alternative DNA sequencing technique came to my mind. The basic concept was to follow the activity of DNA polymerase during nucleotide incorporation into a DNA strand by analyzing the pyrophosphate released during the process. Today, the technique is used in multidisciplinary fields in academic, clinical, and industrial settings all over the word. The technique can be used for both single-base sequencing and whole-genome sequencing, depending on the format used. In this chapter I will give my personal account of the development of Pyrosequencing--beginning on a winter day in 1986, when I first envisioned the method--until today, nearly 20 yr later. I will conclude with future prospects for the method.

  • 114.
    Ohlsson, Anna B.
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Landberg, Tommy
    Berglund, Torkel
    KTH, School of Biotechnology (BIO), Biochemistry.
    Greger, Maria
    Increased metal tolerance in Salix by nicotinamide and nicotinic acid2008In: Plant physiology and biochemistry (Paris), ISSN 0981-9428, E-ISSN 1873-2690, Vol. 46, no 7, p. 655-664Article in journal (Refereed)
    Abstract [en]

    We have earlier shown that nicotinamide (NIC) and nicotinic acid (NiA) can induce defence-related metabolism in plant cells; e.g. increase the level of glutathione. Here we investigated if NIC and NiA could increase the metal tolerance in metal sensitive clones of Salix viminalis and whether this would be mediated via increased glutathione level. Salix clones, sensitive or tolerant to zinc (Zn), copper (Cu) and cadmium (Cd) were grown in the presence of heavy metals (Cd, Cu or Zn) or NIC and NiA as well as in combination. In addition, the influence of N-acetyl-cystein (NAC) and L-2-oxothiazolidine 4-carboxylate (OTC), stimulators of reduced glutathione (GSH) biosynthesis, and the glutathione biosynthesis inhibitor buthionine sulfoximine (BSO) was analysed. Tolerance was measured as effects on root and shoot dry weight, and the glutathione and metal concentrations in the tissues were analysed. Results showed that NIC and NiA decreased the toxic effects of Cd, Cu and Zn on growth significantly in sensitive clones, but also to some extent in tolerant clones. However, the glutathione level and metal concentration did not change by NIC or NiA addition. Treatment with NAC, OTC or BSO did not per se influence the sensitivity to Cd, although the glutathione level increased in the presence of NAC and OTC and decreased in response to BSO. The results suggest that NIC and NiA increased the defence against heavy metals but not via glutathione formation per se.

  • 115. Park, S.
    et al.
    Morley, K. L.
    Horsman, G. P.
    Holmquist, M.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Kazlauskas, R. J.
    Focusing mutations into the P. fluorescens esterase binding site increases enantioselectivity more effectively than distant mutations2005In: Chemistry and Biology, ISSN 1074-5521, E-ISSN 1879-1301, Vol. 12, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    Rational design of enzymes with improved properties, such as enantioselectivity, usually focuses mutations within the substrate binding site. On the other hand, directed evolution of enzymes usually targets the entire protein and discovers beneficial mutations far from the substrate binding site. In this paper, we propose an explanation for this discrepancy and show that a combined approach-random mutagenesis within the substrate binding site-is better. To increase the enantioselectivity (E) of a Pseudomonas fluorescens esterase (PFE) toward methyl 3-bromo-2-methylpropionate, we focused mutagenesis into the substrate binding site at Trp28, Val121, Phe198, and Val225. Five of the catalytically active mutants (13%) showed better enantioselectivity than wild-type PFE. The increases in enantioselectivity were higher (up to 5-fold, reaching E = 61) than with mutants identified by random mutagenesis of the entire enzyme.

  • 116.
    Rüdiger, Arne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hendil-Forssell, Peter
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Hedfors, Cecilia
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Trey, Stacy
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. SP Trätek, SP Technical Research Institute of Sweden.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chemoenzymatic Route to Renewable Thermosets Based on a Suberin Monomer2013In: Journal of renewable materials, ISSN 2164-6341, Vol. 1, no 2, p. 124-140Article in journal (Refereed)
    Abstract [en]

    The present study describes the use of an epoxy functional fatty acid, 9,10-epoxy-18-hydroxyoctadecanoic acid (EFA), extracted from birch (Betula pendula) outer bark to produce thermosets. The purified epoxy fatty acid was polymerized by enzyme-catalyzed polycondensation utilizing Candida antarctica lipase B (CalB) to form oligomers with targeted degrees of polymerization (DP) of 3, 6, and 9 and obtained DPs of 2.3, 5.9 and 7.3, respectively. It was determined that it is possible to first enzymatically polymerize and aliphatically endcap the epoxy functional fatty acid resulting in controlled oligomer lengths while also maintaining the epoxy functionality for further reaction by main-chain homo-epoxy cationic photopolymerization. The enzymatic polymerized oligomers were characterized in terms of conversion of the residual epoxy groups (FT-IR), the thermal properties (DSC, TGA) and the purity by MALDI-TOF and 1H-NMR. The amorphous thermoset films with varying degrees of crosslinking resulting from the cationically photopolymerized oligomers, were characterized in terms of their thermal properties and residual epoxy content (FT-IR ATR). The crosslinked polyesters formed insoluble, amorphous, and transparent films. This work demonstrates that thermoset films with designed properties can be effectively made with the use of forest products to reduce the petroleum-based plastics market.

  • 117. Sakthivel, Priya
    et al.
    Wang, Xiongbiao
    Gharizadeh, Baback
    Giscombe, Ricardo
    Pirskanen, Ritva
    Nyrén, Pål
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Lefvert, Ann Kari
    Single-nucleotide polymorphisms in the B7H3 gene are not associated with human autoimmune myasthenia gravis2006In: Journal of Genetics, ISSN 0022-1333, E-ISSN 0973-7731, Vol. 85, no 3, p. 217-220Article in journal (Refereed)
  • 118.
    Simpson, Neil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Takwa, Mohamad
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Johansson, Mats K. G.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Thiol-functionalized poly(omega-pentadecalactone) telechelics for semicrystalline polymer networks2008In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 41, no 10, p. 3613-3619Article in journal (Refereed)
    Abstract [en]

    Semicrystalline macromonomers based on poly(pentadecalactone), PPDL, have been synthesized by the lipase-catalyzed ring-opening of the otherwise chemically inert pentadecalactone monomer. The macromonomers were designed to have reactive thiols as end groups by the appropriate choice of initiator and chain terminator. The thiol functional macromonomers were then used together with ene monomers to give crosslinked thin films after irradiation in the molten state by UV light in the presence of a photoinitiator (Irgacure 65 1). Two different ene monomers were used, i.e., a tetrafunctional norbornene species and a trifunctional allyl ether maleate species, and resulted in semicrystalline cured films when cured with PPDL. An amorphous, commercially available, trifunctional thiol, trimethylolpropane tri(3-mercaptopropionate), TRIS, was also used for network formation in order to better understand the effect of crystallinity. All thiol-ene systems were found to be readily photopolymerised to high conversion. The PPDL-based networks were semicrystalline in the crosslinked state where the degree of crystallinity was found to depend on the nature of the cross-linker. Networks based on TRIS were found to be amorphous.

  • 119. Skjot, Michael
    et al.
    De Maria, Leonardo
    Chatterjee, Robin
    KTH, School of Biotechnology (BIO), Biochemistry.
    Svendsen, Allan
    Patkar, Sharnkant A.
    Ostergaard, Peter R.
    Brask, Jesper
    Understanding the Plasticity of the alpha/beta Hydrolase Fold: Lid Swapping on the Candida antarctica Lipase B Results in Chimeras with Interesting Biocatalytic Properties2009In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 10, no 3, p. 520-527Article in journal (Refereed)
    Abstract [en]

    The Candida antarctica lipase B (CALB) has found very extensive use in biocatalysis reactions. Long molecular dynamics simulations of CALB in explicit aqueous solvent confirmed the high mobility of the regions lining the channel that leads into the active site, in particular, of helices alpha 5 and alpha 10. The simulation also confirmed the function of helix alpha 5 as a lid of the lipase. Replacing it with corresponding lid regions from the CALB homologues from Neurospora crassa and Gibberella zeae resulted in two new CALB mutants. Characterization of these revealed several interesting properties, including increased hydrolytic activity on simple esters, specifically substrates with C. branching on the carboxylic side, and much increased enantioselectivity in hydrolysis of racemic ethyl 2-phenylpropanoate (E > 50), which is a common structure of the profen drug family.

  • 120.
    Spadiut, Oliver
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Tan, Tien-Chye
    KTH, School of Biotechnology (BIO), Biochemistry.
    Pisanelli, Ines
    Haltrich, Dietmar
    Divne, Christina
    KTH, School of Biotechnology (BIO), Biochemistry.
    Importance of the gating segment in the substrate-recognition loop of pyranose 2-oxidase2010In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 277, no 13, p. 2892-2909Article in journal (Refereed)
    Abstract [en]

    Pyranose 2-oxidase from Trametes multicolor is a 270 kDa homotetrameric enzyme that participates in lignocellulose degradation by wood-rotting fungi and oxidizes a variety of aldopyranoses present in lignocellulose to 2-ketoaldoses. The active site in pyranose 2-oxidase is gated by a highly conserved, conformationally degenerate loop (residues 450-461), with a conformer ensemble that can accommodate efficient binding of both electron-donor substrate (sugar) and electron-acceptor substrate (oxygen or quinone compounds) relevant to the sequential reductive and oxidative half-reactions, respectively. To investigate the importance of individual residues in this loop, a systematic mutagenesis approach was used, including alanine-scanning, site-saturation and deletion mutagenesis, and selected variants were characterized by biochemical and crystal-structure analyses. We show that the gating segment (454FSY456) of this loop is particularly important for substrate specificity, discrimination of sugar substrates, turnover half-life and resistance to thermal unfolding, and that three conserved residues (Asp452, Phe454 and Tyr456) are essentially intolerant to substitution. We furthermore propose that the gating segment is of specific importance for the oxidative half-reaction of pyranose 2-oxidase when oxygen is the electron acceptor. Although the position and orientation of the slow substrate 2-deoxy-2-fluoro-glucose when bound in the active site of pyranose 2-oxidase variants is identical to that observed earlier, the substrate-recognition loop in F454N and Y456W displays a high degree of conformational disorder. The present study also lends support to the hypothesis that 1,4-benzoquinone is a physiologically relevant alternative electron acceptor in the oxidative half-reaction.

  • 121. Steffen-Munsberg, F.
    et al.
    Vickers, C.
    Thontowi, A.
    Schätzle, S.
    Meinhardt, T.
    Svedendahl Humble, M.
    Land, Henrik
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Bornscheuer, U. T.
    Höhne, M.
    Revealing the Structural Basis of Promiscuous Amine Transaminase Activity2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 1, p. 154-157Article in journal (Refereed)
  • 122. Steffen-Munsberg, F.
    et al.
    Vickers, C.
    Thontowi, A.
    Schätzle, S.
    Tumlirsch, T.
    Svedendahl Humble, M.
    Land, Henrik
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Bornscheuer, U. T.
    Höhne, M.
    Connecting Unexplored Protein Crystal Structures to Enzymatic Function2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 1, p. 150-153Article in journal (Refereed)
  • 123.
    Svedendahl Humble, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Biocatalytic Promiscuity2011In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 19, p. 3391-3401Article, review/survey (Refereed)
    Abstract [en]

    Enzymes are attractive catalysts because of their promiscuity and their ability to perform highly regio-, chemo- and stereo-selective transformations. Enzyme promiscuity allows optimisation of industrial processes that require reaction conditions different from those in nature. Many enzymes can be used in reactions completely different from the reaction the enzyme originally evolved to perform. Such catalytically promiscuous reactions can be secondary activities hidden behind a native activity and might be discovered either in screening for that particular activity or, alternatively, by chance. Recently, researchers have designed enzymes to show catalytic promiscuity. It is also possible to design new enzymes from scratch by computer modelling (de novo design), but most work published to date starts from a known enzyme backbone. Promiscuous activity might also be induced or enhanced by rational design or directed evolution (or combinations thereof). Enzyme catalytic promiscuity provides fundamental knowledge about enzyme/substrate interactions and the evolution of new enzymes. New enzymes are required by industry, which needs to optimise chemical processes in an environmentally sustainable way. In this review various aspects of enzyme catalytic promiscuity are considered from a biocatalytic perspective.

  • 124.
    Svedendahl Humble, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry.
    Abedu, Vahak
    Federsel, Hans-Jürgen
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Key Amino Acid Residues for Reversed or Improved Enantiospecificity of an omega-Transaminase2012In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 4, no 8, p. 1167-1172Article in journal (Refereed)
    Abstract [en]

    Transaminases inherently possess high enantiospecificity and are valuable tools for stereoselective synthesis of chiral amines in high yield from a ketone and a simple amino donor such as 2-propylamine. Most known ?-transaminases are (S)-selective and there is, therefore, a need of (R)-selective enzymes. We report the successful rational design of an (S)-selective ?-transaminase for reversed and improved enantioselectivity. Previously, engineering performed on this enzyme group was mainly based on directed evolution, with few exceptions. One reason for this is the current lack of 3D structures. We have explored the ?-transaminase from Chromobacterium violaceum and have used a homology modeling/rational design approach to create enzyme variants for which the activity was increased and the enantioselectivity reversed. This work led to the identification of key amino acid residues that control the activity and enantiomeric preference. To increase the enantiospecificity of the C. violaceum ?-transaminase, a possible single point mutation (W60C) in the active site was identified by homology modeling. By site-directed mutagenesis this enzyme variant was created and it displayed an E value improved up to 15-fold. In addition, to reverse the enantiomeric preference of the enzyme, two other point mutations (F88A/A231F) were identified. This double mutation created an enzyme variant, which displayed substrate dependent reversed enantiomeric preference with an E value shifted from 3.9 (S) to 63 (R) for 2-aminotetralin.

  • 125.
    Svedendahl Humble, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry.
    Håkansson, Maria
    Kimbung, Yengo R
    Walse, Björn
    Abedi, Vahak
    Federsel, Hans-Jürgen
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Logan, Derek T
    Crystal structures of the Chromobacterium violaceumω-transaminase reveal major structural rearrangements upon binding of coenzyme PLP.2012In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 279, no 5, p. 779-792Article in journal (Refereed)
    Abstract [en]

    The bacterial ω-transaminase from Chromobacterium violaceum (Cv-ωTA, EC2.6.1.18) catalyses industrially important transamination reactions by use of the coenzyme pyridoxal 5'-phosphate (PLP). Here, we present four crystal structures of Cv-ωTA: two in the apo form, one in the holo form and one in an intermediate state, at resolutions between 1.35 and 2.4 Å. The enzyme is a homodimer with a molecular mass of ∼ 100 kDa. Each monomer has an active site at the dimeric interface that involves amino acid residues from both subunits. The apo-Cv-ωTA structure reveals unique 'relaxed' conformations of three critical loops involved in structuring the active site that have not previously been seen in a transaminase. Analysis of the four crystal structures reveals major structural rearrangements involving elements of the large and small domains of both monomers that reorganize the active site in the presence of PLP. The conformational change appears to be triggered by binding of the phosphate group of PLP. Furthermore, one of the apo structures shows a disordered 'roof ' over the PLP-binding site, whereas in the other apo form and the holo form the 'roof' is ordered. Comparison with other known transaminase crystal structures suggests that ordering of the 'roof' structure may be associated with substrate binding in Cv-ωTA and some other transaminases. DATABASE: The atomic coordinates and structure factors for the Chromobacterium violaceumω-transaminase crystal structures can be found in the RCSB Protein Data Bank (http://www.rcsb.org) under the accession codes 4A6U for the holoenzyme, 4A6R for the apo1 form, 4A6T for the apo2 form and 4A72 for the mixed form STRUCTURED DIGITAL ABSTRACT: •  -transaminases and -transaminases bind by dynamic light scattering (View interaction) •  -transaminase and -transaminase bind by x-ray crystallography (View interaction) •  -transaminase and -transaminase bind by x-ray crystallography (View interaction).

  • 126.
    Svedendahl, Maria
    KTH, School of Biotechnology (BIO), Biochemistry.
    Lipase and ω-Transaminase: Biocatalytic Investigations2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In a lipase investigation, Candida antarctica lipase B (CALB) are explored for enzyme catalytic promiscuity. Enzyme catalytic promiscuity is shown by enzymes catalyzing alternative catalytic transformations proceeding via different transition state structures than normal. CALB normally performs hydrolysis reactions by activating and coordinating carboxylic acid/ester substrates in an oxyanion hole prior to nucleophilic attack from an active-site serine resulting in acyl enzyme formation. The idea of utilizing the carbonyl activation oxyanion hole in the active-site of CALB to catalyze promiscuous reactions arose by combining catalytic and structural knowledge about the enzyme with chemical imagination. We choose to explore conjugate addition and direct epoxidation activities in CALB by combining molecular modeling and kinetic experiments. By quantum-chemical calculations, the investigated promiscuous reactions were shown to proceed via ordered reaction mechanisms that differ from the native ping pong bi bi reaction mechanism. The investigated promiscuous activities were shown to take place in the enzyme active-site by various kinetic experiments, but despite this, no enantioselectivity was displayed. The reason for this is unknown, but can be a result of a too voluminous active-site or the lack of covalent coordination of the substrates during enzyme-catalysis (Paper I-IV). Combining enzyme structural knowledge with chemical imagination may provide numerous novel enzyme activities to be discovered. In an ω-transaminase investigation, two (S)-selective ω-transaminases from Arthrobacter citreus (Ac-ωTA) and Chromobacterium violaceum (Cv-ωTA) are explored aiming to improve their catalytic properties. Structural knowledge of these enzymes was provided by homology modeling. A homology structure of Ac-ωTA was successfully applied for rational design resulting in enzyme variants with improved enantioselectivity. Additionally, a single-point mutation reversed the enantiopreference of the enzyme from (S) to (R), which was further shown to be substrate dependent (Paper V). A homology structure of Cv-ωTA guided the creation of an enzyme variant showing reduced isopropyl amine inhibition.

  • 127.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Branneby, Cecilia
    Lindberg, Lina
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Reversed Enantiopreference of an omega-Transaminase by a Single-Point Mutation2010In: CHEMCATCHEM, ISSN 1867-3880, Vol. 2, no 8, p. 976-980Article in journal (Refereed)
    Abstract [en]

    Altering the characteristics of an active-site loop in an (S)-selective omega-transaminase from Arthrobacter citreus (variant CNB05-01) influences the enantioselectivity. This active-site loop belongs to the second subunit of the dimeric enzyme structure that participates in the coordination of pyridoxal-5'-phosphate (PLP) in the so called "phosphate group binding cup". Three amino acid residues (E326, V328, and Y331) in this loop are selected by homology modeling for site-directed mutagenesis aiming to increase the enzyme enantioselectivity for 4-fluorophenylacetone. By combining these mutations, five enzyme variants are created. The performance of these variants is explored using a model system consisting of isopropylamine and 4-fluorophenylacetone or 4-nitroacetophenone in asymmetric synthesis using a whole-cell system approach. Three of the five variants show increased enantioselectivity for 4-fluorophenylacetone compared to CNB05-01. Variant CNB05-01/Y331C increases the enantioselectivity from 98% ee to over 99.5% ee. A single-point mutation, V328A, turn the (S)-selective omega-transaminase into an (R)-selective enzyme. This switch in enantioselectivity is substrate dependent, exhibiting (R) selectivity for 4-fluorophenylacetone and retaining (S) selectivity for 4-nitroacetophenone. The shift in enantiopreference is further confirmed by molecular docking simulations. Homology modeling is shown to be a powerful tool to target important amino acid residues in this enzyme in order to improve enantioselectivity by rational design.

  • 128.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Branneby, Cecilia
    Lindberg, Lina
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Reversed enantiopreference of an ω-transaminase by a single-point mutationManuscript (preprint) (Other academic)
  • 129.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Carlqvist, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Branneby, Cecilia
    KTH, School of Biotechnology (BIO), Biochemistry.
    Allnér, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Frise, Anton
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Brinck, Tore
    Direct Epoxidation in Candida antarctica Lipase B Studied by Experiment and Theory2008In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 9, no 15, p. 2443-2451Article in journal (Refereed)
    Abstract [en]

    Candida antarctica lipase B (CALB) is a promiscuous serine hydrolase that, besides its native function, catalyzes different side reactions, such as direct epoxidation. A single-point mutant of CALB demonstrated a direct epoxidation reaction mechanism for the epoxidation of alpha,beta-unsaturated aldehydes by hydrogen peroxide in aqueous and organic solution. Mutation of the catalytically active Ser105 to alanine made the previously assumed indirect epoxidation reaction mechanism impossible. Gibbs free energies, activation parameters, and substrate selectivities were determined both computationally and experimentally. The energetics and mechanism for the direct epoxidation in CALB Ser105Ala were investigated that the reaction proceeds through a two step-mechanism with formation of an oxyanionic intermediate. The active-site residue His224 functions as a general acid-base catalyst with support from Asp187. Oxyanion stabilization is facilitated by two hydrogen bonds from Thr40.

  • 130.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry.
    Abedi, Vahak
    AstraZeneca.
    Federsel, Hans-Jürgen
    AstraZeneca.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    From S to R: Key Residues Controlling Enantiomer Preference and Activity in omega-Transaminase2011Conference paper (Refereed)
  • 131.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Branneby, C.
    Abedi, V.
    Wells, A.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    CASCAT: Redesign of omega-Transaminases for Synthesis of Chiral Amines2010In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 150, p. S123-S124Article in journal (Other academic)
    Abstract [en]

    Transaminases (EC 2.6.1.18) are attractive biocatalysts for synthesis of chiral amines and alpha-amino acids. These enzymes catalyze transfer of an amine group from a donor substrate to an acceptor compound using the cofactor pyridoxal-5′-phoshate (PLP). omega-Transaminases are a versatile subgroup of the transaminases that does not require a carboxylic acid group in alpha-position (in contradiction toalpha-transaminases) and hence accept a wider spectrum of ketones or amines. The omega-transaminases are employed industrially for production of both R- and S-enantiopure amines.

    One bottleneck is the unfavourable equilibrium in such reactions run in the synthesis mode. We have developed a one-pot multi-enzyme system in a cascade fashion for equilibrium displacement by removing formed acetone.

    Another issue is the fact that most omega-transaminases show S-selectivity, however a few R-selective strains do exist. We have used an S-selective omega-transaminase variant from Arthrobacter citreus and created an R-selective variant by rational redesign using a homology enzyme model. This homology modelling/rational design approach was further explored on an omega-transaminase from Chromobacterium violaceum.

  • 132.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Engelmark Cassimjee, Karim
    KTH, School of Biotechnology (BIO), Biochemistry.
    Branneby, Cecilia
    Cambrex Karlskoga AB.
    Sjöstrand, Ulf
    Cambrex Karlskoga AB.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Rational Redesign of ω-Transaminases2010Conference paper (Refereed)
  • 133.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Exploring Promiscuous Activities in a Lipase2009Conference paper (Refereed)
  • 134.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Fast carbon-carbon bond formation by a promiscuous lipase2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 51, p. 17988-17989Article in journal (Refereed)
  • 135.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Catalytic Promiscuity of a Lipase for Direct Epoxidation Reactions2007In: / [ed] Vicente Gotor, 2007Conference paper (Refereed)
  • 136.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Promiscuous Reactions in Candida antarctica lipase B2008Conference paper (Refereed)
  • 137.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Jovanovic, Biljana
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    A Non-Hydrolytic Lipase Mutant with Michael Addition Activity for Esters in Water2008In: Biocat2008 / [ed] Ralf Grote, Garabed Antranikian, 2008Conference paper (Refereed)
  • 138.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Jovanovic, Biljana
    KTH, School of Biotechnology (BIO), Biochemistry.
    Fransson, Linda
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Suppressed Native Hydrolytic Activity of a Lipase to Reveal Promiscuous Michael Addition Activity in Water2009In: CHEMCATCHEM, ISSN 1867-3880, Vol. 1, no 2, p. 252-258Article in journal (Refereed)
    Abstract [en]

    Suppression of,the,native hydrolytic activity of Pseudozyma antarctica lipase B (PalB) (formerly Candida antarctica lipase B) in water is demonstrated. By replacing the catalytic Ser 105 residue with an alanine unit, promiscuous Michael addition activity is favored. A Michael addition reaction between methyl acrylate and acetylacetone was explored as a model system. For the PalB Ser 105 Ala mutant, the hydrolytic activity was suppressed more than 1000 times and at the same time, the Michael addition activity was increased by a factor of 100. Docking studies and molecular dynamics simulations revealed an increased ability of the PalB Ser 105 Ala mutant to harbor the substrates close to a catalytically competent conformation.

  • 139.
    Syren, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Lindgren, Ebba
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Hoeffken, Hans Wolfgang
    Branneby, Cecilia
    Maurer, Steffen
    Hauer, Bernhard
    Hult, Karl
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Biotechnology (BIO), Biochemistry.
    Increased activity of enzymatic transacylation of acrylates through rational design of lipases2010In: Journal of Molecular Catalysis B: Enzymatic, ISSN 1381-1177, E-ISSN 1873-3158, Vol. 65, no 1-4, p. 3-10Article in journal (Refereed)
    Abstract [en]

    A rational design approach was used to create the mutant Candida antarctica lipase B (CALB, also known as Pseudozyma antarctica lipase B) V190A having a k(cat) three times higher compared to that of the wild type (wt) enzyme for the transacylation of the industrially important compound methyl methacrylate. The enzymatic contribution to the transacylation of various acrylates and corresponding saturated esters was evaluated by comparing the reaction catalysed by CALB wt with the acid (H2SO4) catalysed reaction. The performances of CALB wt and mutants were compared to two other hydrolases, Humicola insolens cutinase and Rhizomucor mihei lipase. The low reaction rates of enzyme catalysed transacylation of acrylates were found to be caused mainly by electronic effects due to the double bond present in this class of molecules. The reduction in rate of enzyme catalysed transacylation of acrylates compared to that of the saturated ester methyl propionate was however less than what could be predicted from the energetic cost of breaking the pi-system of acrylates solely. The nature and concentration of the acyl acceptor was found to have a profound effect on the reaction rate. (C) 2009 Elsevier B.V. All rights reserved.

  • 140.
    Syrén, Per-Olof
    KTH, School of Biotechnology (BIO), Biochemistry.
    On electrostatic effects, minimal motion and other catalytic strategies used by enzymes2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Enzymes are powerful biocatalysts that provide rate accelerations of up to 1019 fold compared to the corresponding uncatalyzed reaction in solution. The origin of the remarkable performance displayed by enzymes has fascinated and puzzled researchers for over a hundred years. It is clear that the catalytic effect is a consequence of the higher degree of transition state stabilization for the enzyme catalyzed reaction compared to the corresponding uncatalyzed reaction. It is still not well understood exactly how this transition state stabilization occurs and the relative importance of various catalytic effects are discussed. Catalytic effects involving electrostatics, near attack conformers, dynamic effects and an economy in atomic motion are discussed in this thesis.

    The importance of electrostatic effects is corroborated in this thesis. A single hydrogen bond in transition state constitutes an important difference between amidases and esterases. A hydrogen bond in transition state is found in all sixteen analyzed amidases representing ten different reaction mechanisms and eleven different folding families. The hydrogen bond is shown to be either substrate assisted or enzyme assisted. The role of this hydrogen bond is to assist nitrogen inversion in amidases. Esterases lack this interaction in transition state and therefore they are very poor catalysts in the hydrolysis of amides. Electrostatic interactions are found to facilitate proton transfer that enhances the rate of lipase catalyzed N-acylation of amino alcohols.

    In this thesis electrostatic effects in the substrate are shown to be important for the lipase catalyzed transacylation of acrylates The α,β-double bond present in acrylates introduce electronic effects that has the consequence of restricting the conformational freedom of the substrate in its ground state to two flat conformations, s-cis and s-trans. It is shown that acrylates form near attack conformers (NACs) from their ground state s-cis/s-trans planar conformations. The ability of the enzyme to accommodate such apparent s-cis/s-trans substrate conformations dictates the probability to form productive transition states and thus the reaction rate.

    Dynamic effects are important in enzymes. In this thesis it is found that a point mutation increases the flexibility of a neighbouring residue in Candida antarctica lipase B. This allows the mutated enzyme to explore conformations not accessible for the wild-type enzyme. The dynamics has the effect to decrease steric interactions in transition state with concomitant rate increase for the transacylation of methyl methacrylate.

    In this thesis an economy of atomic motion during enzyme catalysis is observed. Nitrogen inversion in amidases constitutes an interesting example. A rotation as part of the reaction mechanism for amide bond hydrolysis would involve much more motion.

  • 141.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Hendil-Forssell, Peter
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Aumailley, Lucie
    Besenmatter, Werner
    Gounine, Farida
    Svendsen, Allan
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry (closed 20130101).
    Esterases with an Introduced Amidase-Like Hydrogen Bond in the Transition State Have Increased Amidase Specificity2012In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 13, no 5, p. 645-648Article in journal (Refereed)
  • 142.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Amidases have a hydrogen bond that facilitates nitrogen inversion but esterases have not2011In: ChemCatChem, ISSN 1867-3899, Vol. 3, no 5, p. 853-860Article in journal (Refereed)
    Abstract [en]

    The fact that proteases/amidases can hydrolyze amides efficiently whereas esterases can not has been discussed during the last decades. By using molecular modeling we have found a hydrogen bond in the transition state for protease/amidase catalyzed hydrolysis of peptides and amides donated by the scissile NH-group of the substrate. The hydrogen-bond acceptor was found either in the enzyme (enzyme assisted) or in the substrate (substrate assisted). This new interaction with the NH-hydrogen in the transition state (TS) was found in sixteen proteases/amidases, which represent ten different reaction mechanisms and eleven different folding families. Esterases lack this interaction and, therefore, they are slow in hydrolyzing amides. By mimicking the substrate-assisted catalysis found in amidases we were able to shift reaction specificity of amide over ester synthesis of Candida antarctica lipase B one hundred fold. We propose that the hydrogen bond facilitates nitrogen inversion in amidases.

  • 143.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Substrate Conformations Set the Rate of Enzymatic Acrylation by Lipases2010In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 11, no 6, p. 802-810Article in journal (Refereed)
    Abstract [en]

    Acrylates represent a class of 4-unsaturated compounds of high industrial importance. We investigated the influence of substrate conformations on the experimentally determined reaction rates of the enzyme-catalysed transacylation of methyl acrylate and derivatives by ab initio DFT B3LYP calculations and molecular dynamics simulations. The results supported a least-motion mechanism upon the sp(2) to sp(3) substrate transition to reach the transition state in the enzyme active site. This was in accordance with our hypothesis that acrylates form productive transition states from their low-energy s-sis/s-trans conformations. Apparent k(cat) values were measured for Candida antarctica lipase B (CALB), Humicola insolens cutinase and Rhizomucor miehei lipase and were compared to results from computer simulations. More potent enzymes for acryltransfer, such as the CALB mutant V190A and acrylates with higher turnover numbers, showed elevated populations of productive transition states.

  • 144.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Le Joubioux, Florian
    Ben Henda, Yesmine
    Maugard, Thierry
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Graber, Marianne
    Proton Shuttle Mechanism in the Transition State of Lipase-Catalyzed N-Acylation of Amino Alcohols2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 7, p. 1842-1853Article in journal (Refereed)
    Abstract [en]

    An increased reaction rate for lipase-catalyzed N-acylation of amino alcohols relative to that of monofunctionalized amines can be explained by a hydrogen shuttling mechanism that avoids nitrogen inversion in the transition state. The mechanism does not involve acyl migration from an ester intermediate that would be formed first, an explanation that permeates the literature. Our suggested reaction mechanism is dependent on the preference of amino alcohols to form intramolecular hydrogen bonds and the capability of the enzyme to accommodate and exploit the specific hydrogen bonding pattern provided by the ligand during catalysis. Our proposed proton shuttle mechanism involves the transfer of two protons in the transition state concomitant with a nucleophilic attack on the acyl enzyme and provides an explanation for the high reaction rate and chemoselectivity for lipase-catalyzed N-acylation of amino alcohols. Moreover, the proton shuttle mechanism explains the increased reaction rate for the enzyme-catalyzed N-acylation of diamines and of methoxy-2-propylamine, for which O- to N-acyl migration is impossible. A linear free-energy relationship analysis based on the experimental results showed that all of our investigated difunctionalized amine substrates afforded a substrate-assisted rate acceleration of the N-acylation by the same reaction mechanism. Furthermore, the results of the analysis were consistent with partial proton transfer in the rate-limiting transition state, which further supports our suggested proton shuttle mechanism.

  • 145.
    Syrén, Per-Olof
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Le Joubioux, Florian
    Henda, Jesmine Ben
    Maugard, Thierry
    Graber, Marianne
    Proton transfer in amino alcohols in transition state of lipase catalyzed N-acylation.Manuscript (preprint) (Other academic)
  • 146.
    Takwa, Mohamad
    KTH, School of Biotechnology (BIO), Biochemistry.
    Enzymatic Synthesis of Functional Polyesters2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Enzymes are successfully employed in the synthesis of different types of polymers. Candida antarctica lipase B is a highly efficient catalyst for the synthesis of polyesters by ring opening polymerization. ω-Pentadecalactone is an interesting lactone due to the unique proprieties of its polymer (poly-pentadecalactone). These polymers have not been applied in any industrial application due to the difficulties to reach them by chemical polymerization. Enzymatically, poly-pentadecalactone macromonomers can be obtained to high conversion.

    In this investigation we synthesized difunctionalized poly-pentadecalactone with different functional groups. Taking advantage of the selectivity of Candida antarctica lipase B, we introduced different functional end groups. α,ω-Difunctionalized poly-pentadecalactone macromonomers with two thiol ends, two (meth)acrylate ends or with one thiol and one acrylate end were obtained with a high degree of functional ends. We have improved the difunctionalization procedure to a single-step route for the synthesis of α,ω-functionalized poly-pentadecalactones. This procedure has a great potential for industrial applications due to the simplicity of the process and the clean products afforded. Macromonomers with functionalized ends can be used to obtain new polymer architectures with novel proprieties.

    We also show how the use of enzymes could have some limitations when using an initiator with a cleavable ester bond. 2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the ring opening polymerization (eROP) of ε-caprolactone and ω-pentadecalactone aiming for methacrylate functional polyester. However, the lipase catalyzed not only the ring opening polymerization but also the cleavage of the HEMA moiety resulting in a mixture of polymer products with various end groups. A kinetics study of the eROP and the transesterification processes when using HEMA showed that the transesterification processes occurs at moderate frequency at low monomer concentration, it becomes dominant at longer reaction times. We showed that fully difunctionalized polymers can be obtained when using HEMA as initiator for the eROP of lactones by adding a proper end capper.

  • 147.
    Takwa, Mohamad
    KTH, School of Biotechnology (BIO), Biochemistry.
    Lipase Specificity and Selectivity: Engineering, Kinetics and Applied Catalysis2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The specificity and selectivity of the enzyme Candida antarctica lipase B (CALB) were studiedfor several substrates and applications.With help of molecular modeling, the active site of CALB was redesigned for the ring openingpolymerization of D,D‐lactide. Two mutants, with about 90‐fold increase in activity ascompared to the wild‐type enzyme, were created. Changing a glutamine into alanineaccounted for this increase in both mutants by creating a larger space in the acyl donorpocket. The new space made it possible to accommodate the bulky substrate and improvethe transition state‐active site complementarity during polymer chain propagation.The enantioselectivity of CALB towards secondary alcohols was engineered by rationalredesign of the stereoselectivity pocket in the enzyme active site. A larger space created by asingle point mutation resulted in an 8’300’000 times change in enantioselectivity towards 1‐phenylethanol and the enantiopreference was inverted into S‐preference. The activitytowards the S‐enantiomer increased 64’000 times in the mutant as related to the wild‐type.The solvent and temperature effects on the enantioselectivity were studied for severalsubstrates and revealed the importance of entropy in the change in enantioselectivity.Substrate selectivity is of great importance for the outcome of enzyme catalyzed polymersynthesis. Ring opening polymerization (ROP) of γ‐acyloxy‐ε‐caprolactones will result in apolyester chain with pendant functional groups. CALB was found to have activity not onlytowards the lactone but also towards the γ‐ester leading to rearrangement of the monomersyielding γ‐acetyloxyethyl‐γ‐butyrolactone. This selectivity between the lactone and the γ‐ester was dependent on the type of group in the γ position and determined the ratio ofpolymerization and rearrangement of the monomers. Molecular dynamics simulations wereused to gain molecular understanding of the selectivity between the lactone and γ‐ester.In order to obtain (meth)acrylate functional polyesters we investigated the use of 2‐hydroxyethyl (meth)acrylate (HEA and HEMA) as initiators for ring opening polymerization.We found that, in addition to the ring opening polymerization activity, CALB catalyzed thetransacylation of the acid moiety of the initiators. The selectivity of CALB towards thedifferent acyl donors in the reaction resulted in a mixture of polymers with different endgroups. A kinetic investigation of the reaction showed the product distribution with timewhen using HEA or HEMA with ε‐caprolactone or ω‐pentadecalactone.The high selectivity of CALB towards lactones over (meth)acrylate esters such as ethyleneglycol di(meth)acrylate was used to design a single‐step route for the synthesis ofdi(meth)acrylated polymers. By mixing ω‐pentadecalactone with the ethylene glycoldi(meth)acrylate and the enzyme in solvent free conditions, we obtained >95 % ofdi(meth)acrylated polypentadecalactone.Taking advantage of the high chemoselectivity of CALB, it was possible to synthesizepolyesters with thiol and/or acrylate functional ends. When using a thioalcohol as initiatorCALB showed high selectivity towards the alcohol group over the thiol group as acyl acceptorfor the ROP reaction. The enzymatic ability of catalyzing simultaneous reactions (ROP andtransacylation) it was possible to develop a single‐step route for the synthesis ofdifunctionalized polyesters with two thiol ends or one thiol and one acrylate end by mixingthe initiator, lactone and a terminator.

  • 148.
    Takwa, Mohamad
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry.
    Single-step, solvent-free enzymatic route to alpha,omega-functionalized polypentadecalactone macromonomers2008In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 41, no 14, p. 5230-5236Article in journal (Refereed)
    Abstract [en]

    A straightforward enzymatic single-step route toward the synthesis of alpha,omega-functionalized polypentadecalactone (PPDL) macromonomers containing dithiol, thiol-acrylate, diacrylate, or dimethacrylate end groups has been developed. Two solvent-free approaches, mixing all components at start, using Candida antarctica lipase B (CALB) as an efficient catalyst were demonstrated. In the first approach difunctionalized polymers (with dithiol or thiol-acrylate end groups) were synthesized by mixing lipase, lactone, and equimolar amounts of functional initiator (6-mercapto-1-hexanol) and terminator (11-mercapto-1-undecanoic acid or vinyl acrylate). Polymers with a high fraction (95%) of dithiol end groups or polymers with thiol-acrylate end groups (86% and 96%, respectively) were obtained. In the second approach, a functional diester (ethylene glycol diacrylate or ethylene glycol dimethacrylate) was mixed with lactone and lipase without predrying, using water as an initial initiator. Reduced pressure was applied after 2 h of incubation to evaporate water and push the equilibrium toward high functionalization. Polymers with >96% diacrylated or dimethacrylated end groups were achieved.

  • 149.
    Takwa, Mohamad
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Simpson, Neil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry.
    One-Pot Difunctionalization of Poly-(ω-pentadecalactone) with Thiol-Thiol or Thiol-Acrylate Groups, Catalyzed by Candida antarctica Lipase B2006In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 27, no 22, p. 1932-1936Article in journal (Refereed)
    Abstract [en]

    An enzymatic one-pot procedure has been developed for the synthesis of difunetional polyesters containing terminal thiols and acrylates. Candida antarctica lipase B was used as a catalyst for the ring-opening polymerization of ω-pentadecalactone. The polymerization was initiated with 6-mercaptohexanol, then terminated with γ-thiobutyrolactone or vinyl acrylate to create two types of difunetional polyesters with a very high content of thiol-thiol or thiolacrylate end-groups.

  • 150.
    Takwa, Mohamad
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Wittrup Larsen, Marianne
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Martinelle, Mats
    KTH, School of Biotechnology (BIO), Biochemistry.
    Rational redesign of Candida antarctica lipase B for the ring opening polymerization of D,D-lactide2011In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, no 26, p. 7392-7394Article in journal (Refereed)
    Abstract [en]

    Based on molecular modelling, the enzyme Candida antarctica lipase B was redesigned as a catalyst for the ring opening polymerization of D, D-lactide. Two mutants with 90-fold increased activity as compared to the wild-type enzyme were created. In a preparative synthesis of poly(D,D-lactide) the mutants greatly improved the rate and the degree of polymerization.

1234 101 - 150 of 167
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf