Fig. 1: Lignin structure, S-lignin demethylases and P450 catalytic cycle.
From: Structural insights into S-lignin O-demethylation via a rare class of heme peroxygenase enzymes
a Overall structure of lignin highlighting the main p-coumaryl (p-hydroxyphenyl, H-type, blue), coniferyl (guaiacyl, G-type, purple) and sinapyl (syringyl, S-type, green) alcohol subunits. b Schemes showing the O-demethylation reactions of S-lignin aromatics catalyzed by tetrahydrofolate-dependent demethylases DesA, LigM, and DmtS from Sphingobium sp. SYK-6 and Novosphingobium aromaticivorans DSM 12444 (pink), the Rieske non-heme iron-dependent oxygenase VanAB from Pseudomonas putida KT2440 (blue) and the cytochrome P450s SyoA and GcoA from Amycolatopsis thermoflava (orange). The target O-methyl groups for each enzyme are denoted by dashed circles colored by enzyme family. c Catalytic cycle of cytochrome P450s showing the monooxygenase pathway (outer circle) and the peroxide shunt pathway generating the transient intermediate hydroperoxo-ferric complex Compound 0 (Cpd 0), leading to formation of the reactive species Compound I (Cpd I). The oxidation state of Fe is indicated with a purple gradient; FeII light, FeIII medium, and FeIV-oxo/porphyrin radical cation, dark purple.
