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: An extended loop in CE7 carbohydrate esterase family is dispensable for oligomerization but required for activity and thermostability Singh MK, Manoj N Ref: J Struct Biol, 194:434, 2016 : PubMed
The carbohydrate esterase family 7 (CE7) belonging to the alpha/beta hydrolase superfamily contains a structurally conserved loop extension element relative to the canonical alpha/beta hydrolase fold. This element called the beta-interface loop contributes 20-30% of the total buried surface area at intersubunit interfaces of the functional hexameric state. To test whether this loop is an enabling region for the structure and function of the oligomeric assembly, we designed a truncation variant of the thermostable CE7 acetyl esterase from Thermotoga maritima (TmAcE). Although deletion of 26 out of 40 residues in the loop had little impact on the hexamer formation, the variant exhibited altered dynamics of the oligomeric assembly and a loss of thermal stability. Furthermore, the mutant lacked catalytic activity. Crystal structures of the variant and a new crystal form of the wild type protein determined at 2.75A and 1.76A, respectively, provide a rationale for the properties of the variant. The hexameric assembly in the variant is identical to that of the wild type and differed only in the lack of buried surface area interactions at the original intersubunit interfaces. This is accompanied by disorder in an extended region of the truncated loop that consequently induces disorder in the neighboring oxyanion hole loop. Overall, the results suggest that the beta-interface loop in CE7 enzymes is dispensable for the oligomeric assembly. Rather, the loop extension event was evolutionarily selected to regulate activity, conformational flexibility and thermal stability.
        
Title: Regioselective hydrolysis of peracetylated alpha-D-glycopyranose catalyzed by immobilized lipases in aqueous medium. A facile preparation of useful intermediates for oligosaccharide synthesis Bastida A, Fernandez-Lafuente R, Fernandez-Lorente G, Guisan JM, Pagani G, Terreni M Ref: Bioorganic & Medicinal Chemistry Lett, 9:633, 1999 : PubMed
Penta-O-acetyl-alpha-D-glucopyranose was selectively deacetylated in aqueous media by lipases from Candida cilindracea (CCL) adsorbed on octyl-agarose support. Enzymatic hydrolyses was regioselective at the 4-position under neutral pH and towards the 6 position under acidic conditions. This enzymatic approach allows the one step synthesis of 1,2,3,6-tetra-O-acetyl-alpha-D-glucopyranoses 1, a useful intermediate in oligosaccharide synthesis.
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: Role of an N-terminal extension in stability and catalytic activity of a hyperthermostable alpha/beta hydrolase fold esterase Singh MK, Shivakumaraswamy S, Gummadi SN, Manoj N Ref: Protein Engineering Des Sel, 30:559, 2017 : PubMed
The carbohydrate esterase family 7 (CE7) enzymes catalyze the deacetylation of acetyl esters of a broad range of alcohols and is unique in its activity towards cephalosporin C. The CE7 fold contains a conserved N-terminal extension that distinguishes it from the canonical alpha/beta hydrolase fold. The hexameric quaternary structure indicates that the N-terminus may affect activity and specificity by controlling access of substrates to the buried active sites via an entrance tunnel. In this context, we characterized the catalytic parameters, conformation and thermal stability of two truncation variants lacking four and ten residues of the N-terminal region of the hyperthermostable Thermotoga maritima CE7 acetyl esterase (TmAcE). The truncations did not affect the secondary structure or the fold but modulated the oligomerization dynamics. A modest increase was observed in substrate specificity for acetylated xylose compared with acetylated glucose. A drastic reduction of ~30-40 degrees C in the optimum temperature for activity of the variants indicated lower thermal stability. The loss of hyperthermostability appears to be an indirect effect associated with an increase in the conformational flexibility of an otherwise rigid neighboring loop containing a catalytic triad residue. The results suggest that the N-terminal extension was evolutionarily selected to preserve the stability of the enzyme.
        
Title: An extended loop in CE7 carbohydrate esterase family is dispensable for oligomerization but required for activity and thermostability Singh MK, Manoj N Ref: J Struct Biol, 194:434, 2016 : PubMed
The carbohydrate esterase family 7 (CE7) belonging to the alpha/beta hydrolase superfamily contains a structurally conserved loop extension element relative to the canonical alpha/beta hydrolase fold. This element called the beta-interface loop contributes 20-30% of the total buried surface area at intersubunit interfaces of the functional hexameric state. To test whether this loop is an enabling region for the structure and function of the oligomeric assembly, we designed a truncation variant of the thermostable CE7 acetyl esterase from Thermotoga maritima (TmAcE). Although deletion of 26 out of 40 residues in the loop had little impact on the hexamer formation, the variant exhibited altered dynamics of the oligomeric assembly and a loss of thermal stability. Furthermore, the mutant lacked catalytic activity. Crystal structures of the variant and a new crystal form of the wild type protein determined at 2.75A and 1.76A, respectively, provide a rationale for the properties of the variant. The hexameric assembly in the variant is identical to that of the wild type and differed only in the lack of buried surface area interactions at the original intersubunit interfaces. This is accompanied by disorder in an extended region of the truncated loop that consequently induces disorder in the neighboring oxyanion hole loop. Overall, the results suggest that the beta-interface loop in CE7 enzymes is dispensable for the oligomeric assembly. Rather, the loop extension event was evolutionarily selected to regulate activity, conformational flexibility and thermal stability.
        
Title: Regioselective enzymatic hydrolysis of acetylated pyranoses and pyranosides using immobilised lipases. An easy chemoenzymatic synthesis of alpha- and beta-D-glucopyranose acetates bearing a free secondary C-4 hydroxyl group Terreni M, Salvetti R, Linati L, Fernandez-Lafuente R, Fernandez-Lorente G, Bastida A, Guisan JM Ref: Carbohydr Res, 337:1615, 2002 : PubMed
Protected sugars with only one free hydroxyl group are useful building blocks for the synthesis of a large number of glycoderivatives. In order to avoid the problems of the classical chemical synthesis, we studied the regioselective enzymatic hydrolysis of different fully acetylated glycopyranoses and glycopyranosides. The main challenge was to obtain the hydrolysis of the substrates in only one position, with high regioselectivity, while avoiding any further hydrolysis towards partially acetylated sugars. Candida rugosa (CRL) and Pseudomonas fluorescens (PFL) lipases (EC 3.1.1.3) immobilised on octyl agarose afforded regioselective hydrolysis only in the 6- and 1-positions, respectively. Furthermore, a new one-pot chemoenzymatic approach has been developed in order to obtain alpha- and beta-protected glucopyranoses bearing a free secondary C-4 hydroxyl group. For instance, 1,2,3,6-tetra-O-acetyl-alpha-D-glucopyranose was easily synthesised in good overall yield (70%) starting from 1,2,3,4,6-penta-O-acetyl-alpha-D-glucopyranose by regioselective enzymatic hydrolysis in the 6-position, catalysed by CRL, followed by a temperature- and pH-controlled acyl migration.
        
Title: Regioselective hydrolysis of peracetylated alpha-D-glycopyranose catalyzed by immobilized lipases in aqueous medium. A facile preparation of useful intermediates for oligosaccharide synthesis Bastida A, Fernandez-Lafuente R, Fernandez-Lorente G, Guisan JM, Pagani G, Terreni M Ref: Bioorganic & Medicinal Chemistry Lett, 9:633, 1999 : PubMed
Penta-O-acetyl-alpha-D-glucopyranose was selectively deacetylated in aqueous media by lipases from Candida cilindracea (CCL) adsorbed on octyl-agarose support. Enzymatic hydrolyses was regioselective at the 4-position under neutral pH and towards the 6 position under acidic conditions. This enzymatic approach allows the one step synthesis of 1,2,3,6-tetra-O-acetyl-alpha-D-glucopyranoses 1, a useful intermediate in oligosaccharide synthesis.