Molecular cloning of carboxylesterase gene and biochemical characterization of encoded protein from Bacillus subtilis (RRL BB1)

An isolated strain of Bacillus subtilis identified by 16S rDNA sequence analysis produces an enantioselective ester hydrolase. Whole cells of B. subtilis (RRL BB1) and enzyme derived from it was capable of enantioselective hydrolysis of several racemates including drug intermediates with moderate to high enantioselectivity as already reported by us. In this communication, we describe cloning of the gene encoding the enantioselective esterase designated as estBB1. The primary structure of the enzyme determined from the nucleotide sequence indicated that esterase estBB1 has Mw approximately 52kDa and pI approximately 5.2 and belongs to the family of type B carboxylesterases with 50-60% similarity at amino acid level. Alignment studies of sequences of the estBB1 and Pnb esterase 56C8 from B. subtilis showed that estBB1 has an alpha/beta hydrolase fold with catalytic triad formed by Ser190, Glu305 and His394 at active site and Ser190 is located in the conserved motif -G-X-S-X-G-.