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Publication Abstract from PubMed

The carbohydrates and glycoconjugates that enter the human gastrointestinal tract (GI) are remarkably complex, and most of the genes encoding the enzymes required for processing these molecules are not present in the human genome. The glycoside hydrolases encoded by the human gut microbiome therefore play an integral role in processing these diverse exogenous and endogenous glycoconjugates. Here, we analyzed three structurally and functionally distinct beta-glucuronidase (GUS) glycoside hydrolases from a single commensal microbe of the human gut, Bacteroides uniformis. Using nine crystal structures and biochemical and biophysical data, we show that although these three proteins share similar overall folds, they exhibit different structural features that create three structurally and functionally unique active sites. Notably, we found that quaternary structure plays an important role in creating distinct active-site features that are difficult to predict via structural modeling methods alone. The enzymes displayed differential processing capabilities toward several glucuronic acid-containing polysaccharides. They also hydrolyzed SN-38-glucuronide, a metabolite of the anticancer drug irinotecan, suggesting that these gut-microbial enzymes could reactivate this drug in the GI. We further demonstrate that GUS-specific and non-selective inhibitors exhibit varying potencies toward each enzyme. Together, these results highlight the diversity of GUS enzymes within a single Bacteroides gut commensal and advance our understanding of how structural properties affect the specific roles of microbial enzymes in processing and catabolizing drug-derived glucuronides and glycan substrates.

Three structurally and functionally distinct beta-glucuronidases from the human gut microbe Bacteroides uniformis.,Pellock SJ, Walton WG, Biernat KA, Torres-Rivera D, Creekmore BC, Xu Y, Liu J, Tripathy A, Stewart LJ, Redinbo MR J Biol Chem. 2018 Oct 9. pii: RA118.005414. doi: 10.1074/jbc.RA118.005414. PMID:30301767^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.