title: A water molecule in the stereospecificity pocket of Candida antarctica lipase B enhances enantioselectivity towards pentan-2-ol.
abstract: 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 rate 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 J mol-1 K-1.
authors.affiliation: Laboratoire de Biotechnologies et Chimie Bio-Organique, Pôle Sciences et Technologies, FRE CNRS 2766, Bâtiment Marie Curie, Université de la Rochelle, Avenue Michel Crépeau, 17042 La Rochelle, Cedex 1, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Léonard
authors.forename: Linda
authors.initials: L
authors.lastname: Fransson
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lamare
authors.forename: Karl
authors.initials: K
authors.lastname: Hult
authors.forename: Marianne
authors.initials: M
authors.lastname: Graber
mesh_terms: D000215:Acylation; D000327:Adsorption; D001665:Binding Sites; D019149:Bioreactors; D002138:Calibration; D002175:Candida / Q000201:enzymology*; D002384:Catalysis; D005656:Fungal Proteins; D006868:Hydrolysis; D016014:Linear Models; D008049:Lipase / Q000737:chemistry / Q000378:metabolism*; D008956:Models, Chemical; D008958:Models, Molecular; D000439:Pentanols / Q000737:chemistry / Q000378:metabolism*; D013237:Stereoisomerism; D013379:Substrate Specificity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D005656:Fungal Proteins; D000439:Pentanols; D014867:Water; D008049:Lipase; C431349:lipase B, Candida antarctica