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: Functional Characterization of a Novel Dactylosporangium Esterase and Its Utilization in the Asymmetric Synthesis of (R)-Methyl Mandelate Deng D, Zhang Y, Sun A, Hu Y Ref: Appl Biochem Biotechnol, 180:228, 2016 : PubMed
One novel esterase DAEst6 was identified from the genome of Dactylosporangium aurantiacum subsp. Hamdenensis NRRL 18085. DAEst6 was further characterized to be an esterase which exhibited high resistance to high pH values. Esterase DAEst6 could resolve racemic methyl mandelate and generate (R)-methyl mandelate, one key drug intermediate, with an enantiomeric excess and a conversion of 99 and 49 %, respectively, after process optimization. The optimal working condition for the preparation of (R)-methyl mandelate through DAEst6 was found to be 10-mM racemic methyl mandelate, no organic co-solvents, pH 7.5, and 40 degrees C, for 5 h. Our work was the first report about the functional characterization of one novel Dactylosporangium esterase and the utilization of one Dactylosporangium esterase in kinetic resolution. Dactylosporangium esterases represented by DAEst6 possess great potential in the generation of valuable chiral drug intermediates and chemicals.
        
Title: Screening and immobilization Burkholderia sp. GXU56 lipase for enantioselective resolution of (R,S)-methyl mandelate Wei HN, Wu B Ref: Appl Biochem Biotechnol, 149:79, 2008 : PubMed
Microorganisms producing lipase were isolated from soil and sewage samples and screened for enantioselective resolution of (R,S)-methyl mandelate to (R)-mandelic acid. A strain designated as GXU56 was obtained and identified as Burkholderia sp. Preparing immobilized GXU56 lipase by simple adsorption on octyl sepharose CL-4B, the optimum temperature was shifted from 40 degrees C (free lipase) to 50 degrees C (immobilized lipase), and the optimum pH was shifted from 8.0 (free lipase) to 7.2 (immobilized lipase). The immobilized enzyme displayed excellent stability in the pH range of 5.0-8.0, at the temperatures below 50 degrees C and in organic solvents compared with free enzyme. Enantioselectivity ratio for (R)-mandelic acid (E) was dramatically improved from 29.2 to more than 300 by applying immobilized lipase in the resolution of (R,S)-methyl mandelate. After five cycles of use of immobilized lipase, conversion and enantiomeric excess of (R)-mandelic acid were 34.5% and 98.5%, respectively, with enantioselectivity ratio for (R)-mandelic acid (E) of 230. Thus, octyl-sepharose-immobilized GXU56 lipase can be used as a bio-resolution reagent for producing (R)-mandelic acid.
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: Functional Characterization of a Novel Dactylosporangium Esterase and Its Utilization in the Asymmetric Synthesis of (R)-Methyl Mandelate Deng D, Zhang Y, Sun A, Hu Y Ref: Appl Biochem Biotechnol, 180:228, 2016 : PubMed
One novel esterase DAEst6 was identified from the genome of Dactylosporangium aurantiacum subsp. Hamdenensis NRRL 18085. DAEst6 was further characterized to be an esterase which exhibited high resistance to high pH values. Esterase DAEst6 could resolve racemic methyl mandelate and generate (R)-methyl mandelate, one key drug intermediate, with an enantiomeric excess and a conversion of 99 and 49 %, respectively, after process optimization. The optimal working condition for the preparation of (R)-methyl mandelate through DAEst6 was found to be 10-mM racemic methyl mandelate, no organic co-solvents, pH 7.5, and 40 degrees C, for 5 h. Our work was the first report about the functional characterization of one novel Dactylosporangium esterase and the utilization of one Dactylosporangium esterase in kinetic resolution. Dactylosporangium esterases represented by DAEst6 possess great potential in the generation of valuable chiral drug intermediates and chemicals.
        
Title: Enhanced enantioselectivity of a carboxyl esterase from Rhodobacter sphaeroides by directed evolution Ma J, Wu L, Guo F, Gu J, Tang X, Jiang L, Liu J, Zhou J, Yu H Ref: Applied Microbiology & Biotechnology, 97:4897, 2013 : PubMed
The present work created an esterase variant from Rhodobacter sphaeroides (RspE) with enhanced selectivity in hydrolytic kinetic resolutions by directed evolution. A "model" substrate, methyl mandelate, was introduced in the high-throughput screening procedure. E values of a variant CH (Asn62Cys/Leu145His) for six different esters were 10-83, which were a relative improvement compared to 2-20 for the wild type. Our subsequent crystal structure interpretation and molecular dynamics simulations helped shed light on the source of enantioselectivity modified by directed evolution. Though mutations displayed no "direct" interaction with the substrate, they were hypothesized to strengthen the intramolecular interaction in the catalytic cavity of variant. Conformation analysis revealed that the enhanced enantioselectivity of variant CH for the seven substrates applied in this study was derived from the decrease in size of the substrate binding pocket.
        
Title: Screening and immobilization Burkholderia sp. GXU56 lipase for enantioselective resolution of (R,S)-methyl mandelate Wei HN, Wu B Ref: Appl Biochem Biotechnol, 149:79, 2008 : PubMed
Microorganisms producing lipase were isolated from soil and sewage samples and screened for enantioselective resolution of (R,S)-methyl mandelate to (R)-mandelic acid. A strain designated as GXU56 was obtained and identified as Burkholderia sp. Preparing immobilized GXU56 lipase by simple adsorption on octyl sepharose CL-4B, the optimum temperature was shifted from 40 degrees C (free lipase) to 50 degrees C (immobilized lipase), and the optimum pH was shifted from 8.0 (free lipase) to 7.2 (immobilized lipase). The immobilized enzyme displayed excellent stability in the pH range of 5.0-8.0, at the temperatures below 50 degrees C and in organic solvents compared with free enzyme. Enantioselectivity ratio for (R)-mandelic acid (E) was dramatically improved from 29.2 to more than 300 by applying immobilized lipase in the resolution of (R,S)-methyl mandelate. After five cycles of use of immobilized lipase, conversion and enantiomeric excess of (R)-mandelic acid were 34.5% and 98.5%, respectively, with enantioselectivity ratio for (R)-mandelic acid (E) of 230. Thus, octyl-sepharose-immobilized GXU56 lipase can be used as a bio-resolution reagent for producing (R)-mandelic acid.