ABSTRACT:
Toluene
o
‐xylene monooxygenase (ToMO) of
Pseudomonas
sp. OX1 was investigated as a drug‐metabolizing enzyme for the first time and was found to metabolize chlorzoxazone and resveratrol to form human metabolites 6‐chlorzoxazone (0.045 ± 0.016 nmol/hr/mg protein) and piceatannol (0.014 ± 0.009 nmol/hr/mg protein), respectively, though at low rates. ToMO also forms 2‐acetamidophenol (2‐AAP, 27%), 3‐AAP (42%), and 4‐AAP (31%) from acetanilide at 3.6 ± 0.3 nmol/hr/mg protein. Multiple‐site saturation mutagenesis at positions I100/E103/A107 of the alpha‐subunit along with site‐directed mutagenesis approaches were used to isolate thirty‐seven different ToMO variants with enhanced activities and/or fine‐tuned specificities. Specifically, variant I100V/E103T was identified with 2.1‐ and 49‐fold higher activities towards acetanilide and chlorzoxazone, respectively, compared to native ToMO. Variant I100V/E103T also had the regiospecificity of acetanilide change from 31% to 100% 4‐AAP, mimicking human liver enzyme behavior. In addition, several variants showed up to 3.7‐, 1.6‐, and 3.2‐fold improved selectivity for 2‐, 3‐, and 4‐AAP formation, respectively. For resveratrol, variant I100T/E103L was a better catalyst than native ToMO, exhibiting 34‐fold higher activity. The results presented here demonstrate the potential of nonhuman ToMO variants in drug metabolism and contribute to the list of research on probing this promising enzyme.