Copper-Dependent Polysaccharide Monooxygenases: Mechanism and Function

Polysaccharide monooxygenases (PMOs) constitute a superfamily of enzymes that hydroxylate carbon atoms in glycosidic bonds, ultimately leading to the degradation of carbohydrate polymers. PMOs catalyze this challenging transformation at a mononuclear copper site and utilize either O 2 or H 2 O 2 as a cosubstrate. In this review, the mechanisms of three types of catalytic chemistry are discussed: monooxygenase (O 2 as a cosubstrate), oxidase (O 2 reduction to H 2 O 2 ), and peroxygenase (H 2 O 2 as a cosubstrate). Key discoveries in the understanding of PMO mechanism and function are described. Several important questions remain unanswered about the utilization of O 2 and H 2 O 2 as cosubstrates for polysaccharide hydroxylation. This review will summarize the progress toward understanding the mechanism of O 2 activation by this unique class of monooxygenases.