Abstract
A thermostable esterase gene (hydS14) was cloned from an Actinomadura sp. S14 gene library. The gene is 777 bp in length and encodes a polypeptide of 258 amino acid residues with no signal peptide, no N-glycosylation site and a predicted molecular mass of 26,604 Da. The encoded protein contains the pentapeptide motif (GYSLG) and catalytic triad (Ser88-Asp208-His235) of the esterase/lipase superfamily. The HydS14 sequence shows 46%–64% identity to 23 sequences from actinomycetes (23 α/β-hydrolases), has three conserved regions, and contains the novel motif (GY(F)SLG), which distinguishes it from other clusters in the α/β-hydrolase structural superfamily. A plasmid containing the coding region (pPICZαA-hydS14) was used to express HydS14 in Pichia pastoris under the control of the AOXI promoter. The recombinant HydS14 collected from the supernatant had a molecular mass of ~30 kDa, which agrees with its predicted molecular mass without N-glycosylation. HydS14 had an optimum temperature of approximately 70 °C and an optimum pH of 8.0. HydS14 was stable at 50 and 60 °C for 120 min, with residual activities of above 80% and above 90%, respectively, as well as 50% activity at pH 6.0–8.0 and pH 9.0, respectively. The enzyme showed higher activity with p-nitrophenyl-C2 and C4. The Km and Vmax values for p-nitrophenyl-C4 were 0.21 ± 0.02 mM and 37.07 ± 1.04 μmol/min/mg, respectively. The enzyme was active toward short-chain p-nitrophenyl ester (C2–C6), displaying optimal activity with p-nitrophenyl-C4 (Kcat/Km = 11.74 mM−1·S−1). In summary, HydS14 is a thermostable esterase from Actinomadura sp. S14 that has been cloned and expressed for the first time in Pichia pastoris.
Highlights
Lipolytic enzymes, including lipases, triacylglycerol hydrolases (EC 3.1.1.3), esterases, and carboxylester hydrolases (EC 3.1.1.1) are among the most important groups of biocatalysts for biotechnological applications
This study focused on the cloning and characterization of a thermostable esterase from Actinomadura sp
The esterase activities of approximately 15,000 transformants from an Actinomadura sp. strain S14 genomic library were screened for the formation of a clear zone on low-salt LB agar supplemented with
Summary
Lipolytic enzymes, including lipases, triacylglycerol hydrolases (EC 3.1.1.3), esterases, and carboxylester hydrolases (EC 3.1.1.1) are among the most important groups of biocatalysts for biotechnological applications. Montoro-Garcia et al [6] identified a new thermostable carboxylase (Est30) from Geobacillus kaustophilus HTA426, and Rao et al [7] reported a thermostable esterase (EstA3) from Thermoanaerobacter tengcongensis MB4, proposing the introduction of novel families (totally 14 families) based on the sequences of EstA3 and other previously reported esterases These proteins were designated as family XI (LipG), family XII (LipEH166), family XIII (Est30) and family XIV (EstA3). Cutinases are often categorized as a third group, and these enzymes show a preference for substrates esterified with C4–C8 acyl groups, cutin (a natural polymeric material), and synthetic polyesters [9] These enzymes all belong to the α/β-hydrolase structural superfamily and exhibit common parallel β-strands surrounded by α-helical connections. HydS14 was characterized as a new type of esterase in the lipase superfamily
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