Vibrio mimicus arylesterase has thioesterase and chymotrypsin-like activity

A Vibrio mimicus serine arylesterase and an Escherichia coli thioesterase/serine protease share 49.4% amino acid identity. The arylesterase has thioesterase activity for benzoyl-CoA and chymotrypsin-like activity for N-carbobenzoxy-L-phenylalanine p-nitrophenyl ester (NBPNPE). The gene encoding the V. mimicus enzyme is designated etpA. Substituting Ser31 of the V. mimicus enzyme with a glycine or an alanine altered its activity. In comparison with wild type enzyme, the S31A enzyme showed a 5-fold increase and 57% decrease in the catalytic efficiency for benzoyl-CoA and NBPNPE, respectively, and the S31G enzyme showed a 3.6-fold increase and 43% decrease in the catalytic efficiency for benzoyl-CoA and NBPNPE, respectively. For the two mutant enzymes an 8-fold decrease and a 6- to 7-fold increase in Km were seen for benzoyl-CoA and NBPNPE, respectively. The mutagenesis results prove that residue 31 plays an important role in the substrate-specificity.