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A water molecule in the stereospecificity pocket of Candida antarctica lipase B enhances enantioselectivity towards pentan-2-ol.

Léonard V, Fransson L, Lamare S, Hult K, Graber M

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.

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.

Published 5 April 2007 in Chembiochem, 8(6): 662-7.
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