TY - JOUR
T1 - Molecular basis for the enantio- and diastereoselectivity of burkholderia cepacia lipase toward γ-Butyrolactone primary alcohols
AU - Eum, Heesung
AU - Kazlauskas, Romas J.
AU - Ha, Hyun Joon
N1 - Publisher Copyright:
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
PY - 2014/11/24
Y1 - 2014/11/24
N2 - Burkholderia cepacia lipase (BCL) shows high enantioselectivity toward chiral primary alcohols, but this enantioselectivity is often unpredictable, especially for substrates that contain an oxygen at the stereocenter. For example, BCL resolves bsubstituted- g-acetyloxymethyl-g-butyrolactones (acetates of a chiral primary alcohol) by hydrolysis of the acetate, but the enantioselectivity varies with the nature and orientation of the b-alkyl substituent. BCL favors the (R)-primary alcohol when the balkyl substituent is hydrogen (E=30) or trans methyl (E=38), but the (S)-primary alcohol when it is cis methyl (E=145). To rationalize this unusual selectivity, we used a combination of experiments to show the importance of polar interactions and modeling to reveal differences in orientations of the enantiomers. Removal of either the lactone carbonyl in the substrate or the polar side chains in the enzyme by using a related enzyme without these side chains decreased the enantioselectivity at least four-fold. Modeling revealed that the slow enantiomers do not bind by exchanging the location of two substituents relative to the fast enantiomer. Instead, three substituents remain in the same region, but the fourth substituent, hydrogen, inverts to a new location, like an umbrella in a strong wind. In this orientation the favored stereoisomers have similar shapes, thus accounting for the unusual stereoselectivity. The ratio of catalytically productive orientations for the fast vs. slow enantiomers in a molecular dynamic simulation correlated (R2=0.82) with the degree of enantioselectivity including the case where the enantioselectivity reversed. Weighting this ratio by the ratio of Hbonds in the polar interaction to account for different binding strengths improved the correlation with the measured enantioselectivity to R2=0.97. The modeling identifies key interactions responsible for high enantioselectivity in this class of substrates.
AB - Burkholderia cepacia lipase (BCL) shows high enantioselectivity toward chiral primary alcohols, but this enantioselectivity is often unpredictable, especially for substrates that contain an oxygen at the stereocenter. For example, BCL resolves bsubstituted- g-acetyloxymethyl-g-butyrolactones (acetates of a chiral primary alcohol) by hydrolysis of the acetate, but the enantioselectivity varies with the nature and orientation of the b-alkyl substituent. BCL favors the (R)-primary alcohol when the balkyl substituent is hydrogen (E=30) or trans methyl (E=38), but the (S)-primary alcohol when it is cis methyl (E=145). To rationalize this unusual selectivity, we used a combination of experiments to show the importance of polar interactions and modeling to reveal differences in orientations of the enantiomers. Removal of either the lactone carbonyl in the substrate or the polar side chains in the enzyme by using a related enzyme without these side chains decreased the enantioselectivity at least four-fold. Modeling revealed that the slow enantiomers do not bind by exchanging the location of two substituents relative to the fast enantiomer. Instead, three substituents remain in the same region, but the fourth substituent, hydrogen, inverts to a new location, like an umbrella in a strong wind. In this orientation the favored stereoisomers have similar shapes, thus accounting for the unusual stereoselectivity. The ratio of catalytically productive orientations for the fast vs. slow enantiomers in a molecular dynamic simulation correlated (R2=0.82) with the degree of enantioselectivity including the case where the enantioselectivity reversed. Weighting this ratio by the ratio of Hbonds in the polar interaction to account for different binding strengths improved the correlation with the measured enantioselectivity to R2=0.97. The modeling identifies key interactions responsible for high enantioselectivity in this class of substrates.
KW - Enantioselectivity
KW - Hydrolases
KW - Molecular dynamics
KW - Primary alcohols
KW - Reversed enantioselectivity
KW - γ-butyrolactones
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U2 - 10.1002/adsc.201400510
DO - 10.1002/adsc.201400510
M3 - Article
AN - SCOPUS:84915747293
SN - 1521-6543
VL - 356
SP - 3585
EP - 3599
JO - IUBMB Life
JF - IUBMB Life
IS - 17
ER -