engleski

Molecular basis of enantioselectivity of Burkholderia cepacia lipase toward secondary alcohols

Due to their distinct stereopreferences, lipases are used in enantioselective synthesis of organic compounds and in the resolution of racemic mixtures. Study of kinetic resolutions of racemic sec alcohols in n-hexane with a series of twenty commercially available microbial lipases revealed that Burkholderia (formerly Pseudomonas) cepacia lipase, BCL, is the most efficient in resolving racemic 1-phenoxy-2-butanol (1). Our work presents fine structural details in the enzyme active site responsible for enantioselectivity of the titled lipase. In order to understand better enantioselectivity of the BCL, the protein complexes with the analogues of the fast- (R-inhibitor) and the slow-reacting enantiomer (S-inhibitor) were prepared and their three-dimensional structures determined. The lipase-inhibitor complexes crystallise in the monoclinic space group C2 and are isomorphous to the native protein. The three-dimensional structures reveal that both analogues had reacted with the active site Ser87, forming a covalent complex. The topology of the active site of the lipase complex with R-inhibitor indicates that the active site His is hydrogen-bonded to both the active site Ser and the inhibitor. The active site of the complex with the S-inhibitor lacks the hydrogen bond between the active site His and the inhibitor. This confirms the hypothesis, put forward by Cygler et al. (2) that the lack of this hydrogen bond can account for the differences in reactivity.

Burkholderia cepacia lipase; crystal structure; enantioselectivity; secondary alcohols

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