Esterases receive special attention because their wide distribution in biological systems and environments and their importance for physiology and chemical synthesis. The prediction of esterases substrate promiscuity level from sequence data and the molecular reasons why certain such enzymes are more promiscuous than others, remain to be elucidated. This limits the surveillance of the sequence space for esterases potentially leading to new versatile biocatalysts and new insights into their role in cellular function. Here we performed an extensive analysis of the substrate spectra of 145 phylogenetically and environmentally diverse microbial esterases, when tested with 96 diverse esters. We determined the primary factors shaping their substrate range by analyzing substrate range patterns in combination with structural analysis and protein-ligand simulations. We found a structural parameter that helps ranking (classifying) promiscuity level of esterases from sequence data at 94% accuracy. This parameter, the active site effective volume, exemplifies the topology of the catalytic environment by measuring the active site cavity volume corrected by the relative solvent accessible surface area (SASA) of the catalytic triad. Sequences encoding esterases with active site effective volumes (cavity volume/SASA) above a threshold show greater substrate spectra, which can be further extended in combination with phylogenetic data. This measure provides also a valuable tool for interrogating substrates capable of being converted. This measure, found to be transferred to phosphatases of the haloalkanoic acid dehalogenase superfamily and possibly other enzymatic systems, represents a powerful tool for low-cost bioprospecting for esterases with broad substrate ranges, in large scale sequence datasets.
Title: Efficient regioselective synthesis of 3'-O-crotonylfloxuridine catalysed by Pseudomonas cepacia lipase Zhao Z, Zong M, Li N Ref: Biotechnol Appl Biochem, 52:45, 2009 : PubMed
Pseudomonas cepacia lipase-catalysed preferential acylation of the secondary hydroxy group of FUdR (floxuridine) with vinyl crotonate was carried out in spite of the presence of the primary hydroxy group, and 3'-O-crotonylfloxuridine was prepared successfully for the first time. The isomerization of the double bond of crotonate, which occurs in conventional organic synthesis, could be effectively avoided during the enzymatic acylation. The effects of some key factors such as reaction medium, initial a(w) (water activity), molar ratio of vinyl crotonate to FUdR, FUdR concentration and reaction temperature on the reaction were examined. Under the optimized reaction conditions, the initial reaction rate, substrate conversion and 3'-regioselectivity of the reaction were as high as 24 mM/h, 98% and 85% respectively.
