Lipase from Burkholderia cepacia (BCL) has proven to be a very useful biocatalyst for the resolution of 2-substituted racemic acid derivatives, which are important chiral building blocks. Our previous work showed that enantioselectivity of the wild-type BCL could be improved by chemical engineering of the substrate's molecular structure. From this earlier study, three amino acids (L17, V266 and L287) were proposed as targets for mutagenesis aimed at tailoring enzyme enantioselectivity. In the present work, a small library of 57 BCL single mutants targeted on these three residues was constructed and screened for enantioselectivity towards (R,S)-2-chloro ethyl 2-bromophenylacetate. This led to the fast isolation of three single mutants with a remarkable tenfold enhanced or reversed enantioselectivity. Analysis of substrate docking and access trajectories in the active site was then performed. From this analysis, the construction of 13 double mutants was proposed. Among them, an outstanding improved mutant of BCL was isolated that showed an E value of 178 and a 15-fold enhanced specific activity compared to the parental enzyme; thus, this study demonstrates the efficiency of the semirational engineering strategy.
A novel approach based on efficient path-planning algorithms was applied to investigate the influence of substrate access on Burkholderia cepacia lipase enantioselectivity. The system studied was the transesterification of 2-substituted racemic acid derivatives catalysed by B. cepacia lipase. In silico data provided by this approach showed a fair qualitative agreement with experimental results, and hence the potential of this computational method for fast screening of racemates. In addition, a collision detector algorithm used during the pathway searches enabled the rapid identification of amino acid residues hindering the displacement of substrates along the deep, narrow active-site pocket of B. cepacia lipase and thus provided valuable information to guide the molecular engineering of lipase enantioselectivity.
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