Glycosidic Bond Hydroxylation by Polysaccharide Monooxygenases

Diversity and redundancy of PMOs point to physiological roles beyond catabolism. Loops and key residues on the substrate-binding surface position the polysaccharide substrate for C1 or C4 oxidation. Cosubstrate-dependent mechanisms are employed to hydroxylate the glycosidic bond of polysaccharides. Electrons required for PMO activity are supplied by various extracellular redox mediators. Polysaccharide monooxygenases (PMOs) are mononuclear Cu enzymes that have been intensely studied since the discovery of their role in the oxidative degradation of polysaccharides. PMOs can activate either O2 or H2O2 to hydroxylate the strong C H bond alpha to the glycosidic linkage of various polysaccharides. Many recent advances in our understanding of these enzymes including structure–function relationships, cosubstrate-dependent chemical mechanisms, and electron transfer mediators are the focus of this review. This has led to a clearer view of the reaction chemistry surrounding PMO catalysis. Polysaccharide monooxygenases (PMOs) are mononuclear Cu enzymes that have been intensely studied since the discovery of their role in the oxidative degradation of polysaccharides. PMOs can activate either O2 or H2O2 to hydroxylate the strong C H bond alpha to the glycosidic linkage of various polysaccharides. Many recent advances in our understanding of these enzymes including structure–function relationships, cosubstrate-dependent chemical mechanisms, and electron transfer mediators are the focus of this review. This has led to a clearer view of the reaction chemistry surrounding PMO catalysis. a polysaccharide that is covalently bonded between the alpha anomeric carbon-1 of one monosaccharide and the carbon-4 of another. structural motif found in proteins that comprises two antiparallel β-sheets. a ligand that coordinates a metal ion through two bonds. a protein domain frequently associated with carbohydrate-active enzymes that aids in the binding of polysaccharides. a multidomain flavocytochrome oxidoreductase secreted with fungal PMOs. A flavin-bound dehydrogenase domain oxidizes cellobiose to cellobiono-1,5-lactone and shuttles two electrons through a b-type cytochrome domain to PMOs. a spectroscopic technique used to detect unpaired electrons; can provide electronic structure information on paramagnetic sites. a naturally occurring α-amino acid with an amide side chain. the covalent bond between two carbohydrate residues or a carbohydrate and another group. a post-translational modification of the His1-Nε found on many PMOs of eukaryotic origin. a naturally occurring α-amino acid with a neutral, nonpolar benzyl side chain. a naturally occurring α-amino acid with a 4-hydroxylphenol side chain.