Mechanistic studies of polysaccharide monooxygenases (584.8)

Abstract

Polysaccharide monooxygenases (PMOs) from filamentous fungi have recently been shown to play a central role in oxidative degradation of cellulose. These enzymes contain a mononuclear copper active site on a flat surface of the protein that would allow for direct interaction with the substrate. The active site copper coordination consists of two histidine ligands. One of these ligands is the unusual N‐terminal Ne‐methyl‐histidine residue that binds in a bidentate mode using its imidazole and amino groups. PMOs activate dioxygen leading to hydroxylation of either C1 or C4 position of the glycosidic linkage, which subsequently results in the cleavage of this bond. Newly developed expression methods have enabled the characterizeation and classification of the PMO family into three major groups based on their selectivity toward C1 and C4. Factors that control the regioselectivity of PMOs are underway, including residues that contribute to orientation of the copper site on the cellulose surface. Several PMOs have been identified that hydroxylate soluble cellodextrins to form similar products as observed for cellulose. Oxygen activation by these PMOs is also underway.