The Novel Enantioselective Esterase AopE from <i>Brevundimonas</i> sp. Strain YS Preferentially Catabolizes the ( <i>R</i> )-Enantiomer of the Herbicide Haloxyfop-Methyl

Haloxyfop-methyl is a chiral aryloxyphenoxypropionate (AOPP) with two enantiomeric forms that is widely used throughout the globe and is associated with severe environmental issues. While relatively little remains known of haloxyfop-methyl enantiomeric resolution or the selective degradation of these enantiomers by bacteria. Here, a novel <i>aopE</i> gene capable of catalyzing initial haloxyfop-methyl degradation was cloned from the newly isolated <i>Brevundimonas</i> sp. strain YS. No significant similarity was detected when comparing AopE to other esterases that have undergone biochemical characterization to date. AopE catalyzed the hydrolysis of haloxyfop-methyl to haloxyfop-acid and exhibited enantioselectivity by preferentially processing (<i>R</i>)-(+)-haloxyfop-methyl over its (<i>S</i>)-form. This preference extended to two structural analogues, (<i>R</i>)-(+)-quizalofop-ethyl and (<i>R</i>)-(+)-diclofop-methyl, which share the 4-oxyphenoxypropanoic acid scaffold. Molecular docking, molecular dynamics simulation, and site-directed mutagenesis analyses revealed that the Phe227 residue plays an essential role in the catalytic activity of AopE toward (<i>R</i>)-(+)-haloxyfop-methyl by imposing the π-π T-shaped and π-alkyl interactions. Together, these results offer greater insight into the enantioselective catabolic processing of chiral AOPP herbicides by bacteria.