Abstract
BACKGROUND: Floudas et al. (Science 336: 1715) established that lignin-degrading fungi appeared at the end of Carboniferous period associated with the production of the first ligninolytic peroxidases. Here, the subsequent evolution of these enzymes in Polyporales, where most wood-rotting fungi are included, is experimentally recreated using genomic information. RESULTS: With this purpose, we analyzed the evolutionary pathway leading to the most efficient lignin-degrading peroxidases characterizing Polyporales species. After sequence reconstruction from 113 genes of ten sequenced genomes, the main enzyme intermediates were resurrected and characterized. Biochemical changes were analyzed together with predicted sequences and structures, to understand how these enzymes acquired the ability to degrade lignin and how this ability changed with time. The most probable first peroxidase in Polyporales would be a manganese peroxidase (Mn(3+) oxidizing phenolic lignin) that did not change substantially until the appearance of an exposed tryptophan (oxidizing nonphenolic lignin) originating an ancestral versatile peroxidase. Later, a quick evolution, with loss of the Mn(2+)-binding site, generated the first lignin peroxidase that evolved to the extant form by improving the catalytic efficiency. Increased stability at acidic pH, which strongly increases the oxidizing power of these enzymes, was observed paralleling the appearance of the exposed catalytic tryptophan. CONCLUSIONS: We show how the change in peroxidase catalytic activities meant an evolutionary exploration for more efficient ways of lignin degradation by fungi, a key step for carbon recycling in land ecosystems. The study provides ancestral enzymes with a potential biotechnological interest for the sustainable production of fuels and chemicals in a biomass-based economy.