Mechanistic Insights into Glycoside 3-Oxidases Involved in C-Glycoside Metabolism in Soil Microorganisms

Abstract

C-glycosides are natural products with important biological activities but are recalcitrant to degradation. Glycoside 3-oxidases (G3Oxs) are newly identified bacterial flavo-oxidases from the glucose-methanol-coline (GMC) superfamily that catalyze the oxidation of C-glycosides with the concomitant reduction of O2 to H2O2. This oxidation is followed by C-C acid/base-assisted bond cleavage in two-step C-deglycosylation pathways. Soil and gut microorganisms have different oxidative enzymes, but the details of their catalytic mechanisms are largely unknown. Here, we report that PsGO3x oxidizes at 50,000-fold higher specificity (kcat/Km) the glucose moiety of mangiferin to 3-keto-mangiferin than free D-glucose to 2-keto-glucose. Analysis of PsG3Ox X-ray crystal structures and PsGO3x in complex with glucose and mangiferin, combined with mutagenesis and molecular dynamics simulations, revealed distinctive features in the topology surrounding the active site that favors catalytically competent conformational states suitable for recognition, stabilization, and oxidation of the glucose moiety of mangiferin. Furthermore, their distinction to pyranose 2-oxidases (P2Oxs) involved in wood decay and recycling is discussed from an evolutionary, structural, and functional viewpoint.

Functional metagenomics reveals an alternative, broad-specificity pathway for metabolism of carbohydrates in human gut commensal bacteria

“…More recently, ketosugars have been reported as intermediates in the breakdown of anhydrosugars such as levoglucosan 32,33 , as well as C-glycosidecleaving systems that operate via similar oxidation and elimination reactions. [34][35][36][37][38] As mentioned, other glycosidases that transiently oxidize sugar hydroxy groups as part of their mechanism have been reported by us and others 9,[39][40][41] . However, no similarly broad specificity was observed in any of these cases.…”