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Substrate entropy in enzyme enantioselectivity: An experimental and molecular modeling study of a lipase
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
2002 (English)In: Protein Science, ISSN 0961-8368, E-ISSN 1469-896X, Vol. 11, no 6, 1462-1471 p.Article in journal (Refereed) Published
Abstract [en]

The temperature dependence of the enantioselectivity of Candida antarctica lipase B for 3-hexanol, 2-butanol, 3-methyl-2-butanol, 3,3-dimethyl-2-butanol, and 1-bromo-2-butanol revealed that the differential activation entropy, Delta(R-S)Delta(S)(divided bydivided by)., was as significant as the differential activation enthalpy, Delta(R-S)DeltaH(divided bydivided by), to the enantiomeric ratio, E. 1-Bromo-2-butanol, with isosteric substituents, displayed the largest Delta(R-S)DeltaS(divided bydivided by) 3-Hexanol displayed, contrary to other sec-alcohols, a positive Delta(R-S)DeltaS(divided bydivided by). In other words, for 3-hexanol the preferred R-enantiomer is not only favored by enthalpy but also by entropy. Molecular dynamics (MID) simulations and systematic search calculations of the substrate accessible volume within the active site revealed that the (R)-3-hexanol transition state (TS) accessed a larger volume within the active site than the (S)-3-hexanol TS. This correlates well with the hi-her TS entropy of (R)-3-hexanol. In addition, this enantiomer did also yield a higher number of allowed conformations, N, from the systematic search routines, than did the S-enantiomer. The substrate accessible volume was greater for the enantiomer preferred by entropy also for 2-butanol. For 3,3-dimethyl-2-butanol, however, neither MD-simulations nor systematic search calculations yielded substrate accessible volumes that correlate to TS entropy. Ambiguous results were achieved for 3-methyl-2-butanol.

Place, publisher, year, edition, pages
2002. Vol. 11, no 6, 1462-1471 p.
Keyword [en]
molecular dynamics; systematic search; enthalpy; enantiomeric ratio; Candida antarctica
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-13383DOI: 10.1110/ps.3480102ISI: 000175757900018OAI: oai:DiVA.org:kth-13383DiVA: diva2:324822
Note
QC 20100616Available from: 2010-06-16 Created: 2010-06-16 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Enthalpy and Entropy in Enzyme Catalysis: A Study of Lipase Enantioselectivity
Open this publication in new window or tab >>Enthalpy and Entropy in Enzyme Catalysis: A Study of Lipase Enantioselectivity
2001 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Biocatalysis has become a popular technique in organic synthesis due to high activity and selectivity of enzyme catalyzed reactions. Enantioselectivity is a particularly attractive enzyme property, which is utilized for the production of enantiopure substances. Determination of the temperature dependence of enzyme enantioselectivity allows for thermodynamic analyses that reveal the contribution of differential activation enthalpy, ΔR-SΔH, and entropy, ΔR-SΔS. In the present investigation the influence of substrate structure, variations on enzyme structure and of reaction media on the enantioselectivity of Candida Antarctica lipase B has been studied.

The contribution of enthalpy, ΔR-SΔH, and entropy, TΔR-SΔS, to the differential free energy, ΔR-SΔG, of kinetic resolutions of sec-alcohols were of similar magnitude. Generally the two terms were counteracting, meaning that the enantiomer favored by enthalpy was disfavored by entropy. 3-Hexanol was an exception where the preferred enantiomer was favored both by enthalpy and by entropy. Resolution of 1-bromo-2-butanol revealed non-steric interactions to influence both ΔR-SΔH and ΔR-SΔS. Molecular modeling of the spatial freedom of the enzyme-substrate transition state indicated correlation tothe transition state entropy. The acyl chain length was shown to affect enantioselectivity in transesterifications of a sec-alcohol.

Point mutations in the active site were found to decrease or increase enantioselectivity. The changes were caused by partly compensatory changes in both ΔR-SΔH and ΔR-SΔS. Studies on single and double mutation variants showed that the observed changes were not additive.

Enantioselectivity was strongly affected by the reaction media. Transesterifications of a sec-alcohol catalyzed by Candida Antarctica lipase B was studied in eight liquidorganic solvents and supercritical carbon dioxide. A correlation of enantioselectivity and the molecular volume of the solvent was found.

Differential activation enthalpy, ΔR-SΔH, and entropy, ΔR-SΔS, display a compensatory nature. However this compensation is not perfect, which allows for modifications of enantioselectivity. The components of the thermodynamic parameters are highly complex and interdependent but if their roles are elucidated rational design of enantioselective enzymatic processes may be possible.

 

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2001. [10], 49 p.
Keyword
Biocatalysis, enzyme catalysis, Candida antarctica lipase B, enantioselectivity, enthalpy, entropy, CALB, enantiomeric ratio
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-3216 (URN)91-7283-157-X (ISBN)
Public defence
2001-09-28, 00:00
Note
QC 20100616Available from: 2001-09-12 Created: 2001-09-12 Last updated: 2010-07-22Bibliographically approved
2. Enzyme substrate solvent interactions: a case study on serine hydrolases
Open this publication in new window or tab >>Enzyme substrate solvent interactions: a case study on serine hydrolases
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Reaction rates and selectivities were measured for transacylation of fatty acid esters in solvents catalysed by Candida antarctica lipase B and by cutinase from Humicola insolens. With these enzymes classical water-based enzymology can be expanded to many different solvents allowing large variations in interaction energies between the enzymes, the substrates and the surrounding. Further ,hydrolysis reactions catalysed by Bacillus subtilis esterase 2 were investigated.

Thermodynamics analyses revealed that the enzyme contribution to reaction rate acceleration compared to acid catalysis was purely entropic. On the other hand, studies of differences in activation entropy and enthalpy between enantiomers and between homologous esters showed that high substrate specificity was favoured by enthalpic stabilisation.

Solvent was found to have a profound effect on enzyme catalysis, affecting both reaction rate and selectivity. Differences in substrate solubility will impact enzyme specificity since substrate binding is an equilibrium between enzyme-bound substrate and substrate in free solution. In addition, solven tmolecules were found to act as enzyme inhibitors, showing both competitive and non-competitive behaviour.

In several homologous data series enthalpy-entropy compensation relationships were encountered. A possible extrathermodynamic relationship between enthalpy and entropy can easily be lost under co-varying errors propagated from the experiments. From the data in this thesis, one instance was found of a real enthalpy-entropy compensation that could be distinguished from statistical errors, while other examples could not be verified.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 43 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2008:15
Keyword
lipase, esterase, specificity
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-4867 (URN)978-91-7415-094-0 (ISBN)
Public defence
2008-09-05, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100722Available from: 2008-09-10 Created: 2008-09-05 Last updated: 2011-07-07Bibliographically approved

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