FAD-dependent C -glycoside–metabolizing enzymes in microorganisms: Screening, characterization, and crystal structure analysis

Significance Microbial degradation of C -glycosides is only reported from human intestinal bacteria. This study isolated a C -glycoside–catabolizing bacteria, Microbacterium sp. 5-2b, from soil and identified a C -glycoside–metabolizing enzyme. Surprisingly, while the metabolic pathway of C -glycoside in the strain was similar to that of an intestinal one, the enzyme named CarA catalyzing the initial step of metabolism was completely different from an enzyme identified from the intestinal microorganism; CarA identified as C -glycoside 3-oxidase for C-glycoside metabolism exhibited amino acid sequence similarity to pyranose oxidase family proteins. This study clarified the structure, function, and distribution of the enzyme involved in C -glycoside catabolism and provides insight into the biogeochemical circulation of C -glycosides in nature.