Functional expression of a novel methanol-stable esterase by Geobacillus subterraneus DSM13552 for biocatalytic synthesis of cinnamyl acetate in a solvent-free system

Background: Esterases are widely distributed in nature and have important applications in medical, industrial and physiological. Recently, the increased demand for flavor esters has prompted the search of catalysts like lipases and esterases. Esterases from thermophiles also show thermal stability at elevated temperatures and have become enzymes of special interest in biotechnological applications. Although most of esterases catalyzed reactions are carried out in toxic and inflammable organic solvents, the solvent-free system owning many advantages such as low cost and easy downstream processing. Results: The gene estGSU753 from Geobacillus subterraneus DSM13552 was cloned, sequenced, and overexpressed into Escherichia coli BL21 (DE3). The novel gene has an open reading frame of 753 bp, and encoding 250-amino-acid esterase (EstGSU753). The sequence analysis showed that the protein contains a catalytic triad formed by Ser97, Asp196, and His226, and the Ser of the active site is located in the conserved motif Gly95-X-Ser97-X-Gly99 included in most esterases and lipases. The protein catalyzed the hydrolysis of p-nitrophenyl esters of different acyl chain lengths, and the enzyme specific activity was 70 U/mg with the optimum substrate p-nitrophenyl caprylate. The optimum pH and temperature of the recombinant enzyme were 8.0 and 60°C respectively. The resulting EstGSU753 showed remarkable stability against methanol. After the incubation at 50% methanol for 9 days, EstGSU753 retained 50% of its original activity. Even incubation at 90% methanol for 2100 minutes, EstGSU753 retained 50% of its original activity. Also, the preliminary study of the transesterification shows the potential value in synthesis of short-chain flavor esters in a solvent-free system, and more than 99% conversion was obtained in 6 h (substrate: cinnamyl alcohol, 1.0 M). Conclusions: This is the first report of esterase gene cloning from Geobacillus subterraneus with detailed enzymatic properties. This methanol-stable esterase showed potential value in industrial applications especially in the perfume industry.