Characterization of an enantioselective esterase from the quizalofop-ethyl-transforming strain of Sphingobium sp. QE-1

Abstract

The enantioselective catabolism of the two enantiomers of the aryloxyphenoxypropionate (AOPP) herbicide, quizalofop-ethyl (QE), in environment by microorganisms is of great interest. In this study, Sphingobium sp. strain QE-1, capable of transforming both enantiomers of QE, was successfully isolated. A novel gene qeH, encoding an esterase capable of initially transforming (R)/(S)-QE to (R)/(S)-quizalofop acid [(R)/(S)-QA], was cloned. QeH showed the highest identity (36.9%) to the β-lactamase MT1414, and the purified QeH displayed optimal activity for (R)-QE at 40 °C and pH 7.0. QeH preferentially hydrolyzed (R)-QE than (S)-QE. Based on molecular docking analyses, the distance between the ligand molecule and the coordination atom was shorter when (R)-QE occupied the active sites as compared to that of (S)-QE, which resulted in a stronger ligand binding affinity for (R)-QE. Besides the two enantiomers of QE, QeH could also convert many other AOPP herbicides with different catalytic efficiency (clodinafop-propargyl > fenoxaprop-P-ethyl > fluazifop-P-butyl > cyhalofop-butyl). This study will enhance our understandings of the enantioselective catabolism of AOPP herbicides by microorganisms.