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: Enhancement effect of ethyl-2-methyl acetoacetate on triacylglycerols production by a freshwater microalga, Scenedesmus sp. LX1 Xin L, Hong-Ying H, Jia Y, Yin-Hu W Ref: Bioresour Technol, 101:9819, 2010 : PubMed
Microalgae are very promising in biodiesel production. To reduce the production cost, approaches to enhance lipid and triacylglycerols (TAGs) production by microalgae have gained much attention. Effect of ethyl-2-methyl acetoacetate (EMA) on the lipid and TAGs production by a freshwater microalga, Scenedesmus sp. LX1, was studied in this paper. EMA below a concentration of 2 mg L(-1) had no significant effect on microalgal biomass or lipid production. The biomass and lipid productivity were about 0.47 g L(-1) and 139 mg L(-1), respectively, and the lipid content per biomass was about 30% (w/w). Promisingly, comparing with the one without EMA treatment, under EMA concentrations of 1.0-2.0 mg L(-1) the TAGs content per lipid (about 20% (w/w)) and TAGs productivity (about 23 mg L(-1)) were increased by 79% and 40%, respectively. Therefore, exposing algal cells with trace amount of EMA offers a viable method to enhance the TAGs production in Scenedesmus sp. LX1.
