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- Ottosson, Jenny, et al.
(författare)
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Rational design of enantio selective enzymes requires considerations of entropy
- 2001
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Ingår i: Protein Science. - : Wiley. - 0961-8368 .- 1469-896X. ; 10:9, s. 1769-1774
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Tidskriftsartikel (refereegranskat)abstract
- Entropy was shown to play an equally important role as enthalpy for how enantioselectivity changes when redesigning an enzyme. By studying the temperature dependence of the enantiomeric ratio E of an enantioselective enzyme, its differential activation enthalpy (Delta (R-S)DeltaH(double dagger)) and entropy (Delta (R-S)DeltaS(double dagger)) components can be determined. This was done for the resolution of 3-methyl-2-butanol catalyzed by Candida antarctica lipase B and five variants with one or two point mutations. Delta (R-S)DeltaS(double dagger) was in all cases equally significant as Delta (R-S)DeltaH(double dagger) to E. One variant, T103G, displayed an increase in E, the others a decrease. The altered enantioselectivities of the variants were all related to simultaneous changes in Delta (R-S)DeltaH(double dagger) and Delta (R-S)DeltaS(double dagger). Although the changes in Delta (R-S)DeltaH(double dagger) and Delta (R-S)DeltaS(double dagger) were of a compensatory nature the compensation was not perfect, thereby allowing modifications of E. Both the W104H and the T103G variants displayed larger Delta (R-S)DeltaH(double dagger). than wild type but exhibited a decrease or increase, respectively, in E due to their different relative increase in Delta (R-S)DeltaS(double dagger).
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| 2. |
- Ottosson, Jenny, et al.
(författare)
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Substrate entropy in enzyme enantioselectivity : An experimental and molecular modeling study of a lipase
- 2002
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Ingår i: Protein Science. - : Wiley. - 0961-8368 .- 1469-896X. ; 11:6, s. 1462-1471
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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