Characterization of a novel aryloxyphenoxypropionate herbicide-hydrolyzing carboxylesterase with R-enantiomer preference from Brevundimonas sp. QPT-2

Aryloxyphenoxypropionate (AOPP) herbicides with a chiral center are widely used to selectively remove annual and perennial grasses. However, the study of the enzymes involved in enantioselective degradation of AOPP herbicides is limited. A novel family VIII carboxylesterase gene, estwx , hydrolyzed the ester bond cleavage of AOPP herbicides to form the corresponding acid and alkyl side chain alcohol, was cloned from Brevundimonas sp. strain QPT-2 and overexpressed in E. coli BL21. The purified recombinant EstWX was shown to hydrolyze a wide range of AOPP herbicides with various catalytic efficiencies. The enantioselectivity assay indicated that EstWX preferentially catalyzed the hydrolysis of the R -enantiomer of AOPP herbicides. The S73, K76, Y196 together with W368 residues, especially S73 and Y196, were essential for the catalytic function of the carboxylesterase. EstWX is a promising candidate for the bioremediation of multiple AOPP herbicide-contaminated environments and for future mechanism studies on the enantioselective degradation of chiral AOPP herbicides.