Engineering a Cytochrome P450 for Demethylation of Lignin-Derived Aromatic Aldehydes

Abstract

Biological funneling of lignin-derived aromatic compounds is a promising approach for valorizing its catalytic depolymerization products. Industrial processes for aromatic bioconversion will require efficient enzymes for key reactions, including demethylation of <i>O</i>-methoxy-aryl groups, an essential and often rate-limiting step. The recently characterized GcoAB cytochrome P450 system comprises a coupled monoxygenase (GcoA) and reductase (GcoB) that catalyzes oxidative demethylation of the <i>O-</i>methoxy-aryl group in guaiacol. Here, we evaluate a series of engineered GcoA variants for their ability to demethylate <i>o</i>-and <i>p</i>-vanillin, which are abundant lignin depolymerization products. Two rationally designed, single amino acid substitutions, F169S and T296S, are required to convert GcoA into an efficient catalyst toward the <i>o</i>- and <i>p</i>-isomers of vanillin, respectively. Gain-of-function in each case is explained in light of an extensive series of enzyme-ligand structures, kinetic data, and molecular dynamics simulations. Using strains of <i>Pseudomonas putida</i> KT2440 already optimized for <i>p</i>-vanillin production from ferulate, we demonstrate demethylation by the T296S variant <i>in vivo</i>. This work expands the known aromatic <i>O-</i>demethylation capacity of cytochrome P450 enzymes toward important lignin-derived aromatic monomers.