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Publication Abstract from PubMed

Microbial conversion of aromatic compounds is an emerging and promising strategy for valorization of the plant biopolymer lignin. A critical and often rate-limiting reaction in aromatic catabolism is O-aryl-demethylation of the abundant aromatic methoxy groups in lignin to form diols, which enables subsequent oxidative aromatic ring-opening. Recently, a cytochrome P450 system, GcoAB, was discovered to demethylate guaiacol (2-methoxyphenol), which can be produced from coniferyl alcohol-derived lignin, to form catechol. However, native GcoAB has minimal ability to demethylate syringol (2,6-dimethoxyphenol), the analogous compound that can be produced from sinapyl alcohol-derived lignin. Despite the abundance of sinapyl alcohol-based lignin in plants, no pathway for syringol catabolism has been reported to date. Here we used structure-guided protein engineering to enable microbial syringol utilization with GcoAB. Specifically, a phenylalanine residue (GcoA-F169) interferes with the binding of syringol in the active site, and on mutation to smaller amino acids, efficient syringol O-demethylation is achieved. Crystallography indicates that syringol adopts a productive binding pose in the variant, which molecular dynamics simulations trace to the elimination of steric clash between the highly flexible side chain of GcoA-F169 and the additional methoxy group of syringol. Finally, we demonstrate in vivo syringol turnover in Pseudomonas putida KT2440 with the GcoA-F169A variant. Taken together, our findings highlight the significant potential and plasticity of cytochrome P450 aromatic O-demethylases in the biological conversion of lignin-derived aromatic compounds.

Enabling microbial syringol conversion through structure-guided protein engineering.,Machovina MM, Mallinson SJB, Knott BC, Meyers AW, Garcia-Borras M, Bu L, Gado JE, Oliver A, Schmidt GP, Hinchen DJ, Crowley MF, Johnson CW, Neidle EL, Payne CM, Houk KN, Beckham GT, McGeehan JE, DuBois JL Proc Natl Acad Sci U S A. 2019 Jun 24. pii: 1820001116. doi:, 10.1073/pnas.1820001116. PMID:31235604^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.