Summary White-rot fungi (WRF) are the most effective lignin-degrading organisms in nature. Lignin is a highly methoxylated plant biopolymer, yet the pathways WRF use to metabolize methoxylated aromatic monomeric compounds as carbon sources remain unidentified. Using systems biology, we elucidate the intracellular catabolism of vanillate—a monomethoxylated aromatic compound—by Gelatoporia subvermispora and Trametes versicolor. We identify and biochemically validate a four-enzyme pathway that converts vanillate into β-ketoadipate, which enters central carbon metabolism. Unlike bacteria, which demethylate vanillate before ring-cleavage by intradiol dioxygenases, WRF employ oxidative decarboxylation followed by extradiol dioxygenase-mediated cleavage. A previously uncharacterized hydrolase is also shown to catalyze the terminal step of this pathway. Biochemical and structural approaches reveal non-canonical enzymes, including a highly substrate-specific extradiol dioxygenase and a metal-free, promiscuous reductase that acts on both methoxylated and non-methoxylated intermediates. These findings highlight distinct fungal strategies for aromatic degradation, offering insights into lignin valorization and wood decay mechanisms.
Schwartz et al. (Sat,) studied this question.