Deciphering the Enzyme-Mediated Oxidation of Dehydroabietic Acid and Other Diterpenoid Resin Acids

Cytochrome P450 enzymes are versatile monooxygenase biocatalysts. Members of the bacterial CYP226 family are hypothesized to catalyze the oxidation of diterpenoid resin acids as the first step in their catabolism. Two CYP226 enzymes (CYP226A3 and CYP226A31) from the thermophilic bacterium Zestomonas thermotolerans were characterized. Both could bind the diterpenoids in gum rosin. Oxidation metabolites were formed using peroxide-driven reactions with the wild-type enzymes and variants with modifications at the dioxygen-binding groove. The CYP226A31 enzyme was used to enantioselectively hydroxylate dehydroabietic acid to the 7β-hydroxy metabolite, enabling its isolation and characterization. The crystal structure of the CYP226A31 enzyme was determined with dehydroabietic acid bound, demonstrating a binding mode consistent with the stereoselective product formation and the unusual UV-visible substrate-bound spectrum. This work establishes the role of these enzymes in the oxidation of diterpenoids and provides a foundation for the valorization of complex mixtures of resin acids from renewable bark biomass.