A cold-active esterase with a substrate preference for vinyl esters from a psychrotroph, Acinetobacter sp. strain no. 6: Gene cloning, purification, and characterization

It has recently been shown that fatty acid vinyl esters serve as effective acylating agents for the synthesis of esters by enzymatic transesterification in high yields. To enhance the usefulness of this system at low temperatures, we have searched for the gene coding for a cold-active lipolytic enzyme with a substrate preference for fatty acid vinyl esters and obtained it from the genomic library of Acinetobacter sp. strain no. 6, a psychrotroph isolated from Siberian soil. The gene (termed aelh, 777 bp) encoded a protein of 258 amino acids, and sequence analysis revealed that the enzyme shows a high sequence similarity to β-ketoadipate enol-lactone hydrolase involved in the β-ketoadipate pathway for the bacterial catabolism of benzoic acid. The aelh gene was expressed in the E. coli C600 cells under the control of lac promoter and the expression product was purified to homogeneity and characterized. It was a monomeric esterase preferentially catalyzing the hydrolysis of enol esters, such as fatty acid vinyl esters with a short-chain acyl group. The enzyme was strongly inhibited by phenylmethylsulfonyl fluoride, a specific inhibitor for serine hydrolases. The enzyme could also catalyze transesterification, for example, between vinyl propionate and propanol yielding propyl propionate at 4°C. These results indicate the usefulness of an esterase (termed AELH) for the enzymatic synthesis of esters by transesterification using vinyl esters as an acyl donor.