Biomass-Degradation by Copper Laccases

Revisiting Enzymatic Function, Substrate Specificity and Terminal Electron Acceptors

Laccases catalyze the complete four-electron reduction of dioxygen (O2) to water with concomitant electron withdrawal from the reducing organic substrate. Of particular interest is the mechanism by which laccases oxidize refractory substrates such as lignin, which hold enormous potential to become the primary feedstocks in the production of biofuels and sustainable commodities. In laccase-catalyzed delignification, in order to shuttle holes/electrons between laccase and lignin, small redox active compounds, known as mediators, are used. We are exploring an alternative to this approach by using a series of artificial tryptophan and tyrosine amino acids that can act as “wires” within the protein to move highly oxidative holes from enzyme active sites to the exterior of the protein where the oxidation of bulky lignin polymers can take place. We also probe the ability of laccases to utilize “other” biologically relevant electron acceptors such as nitrogen oxides as their terminal oxidants.