Rhamnogalacturonan-II (RG-II) is the most complex glycan known. It has been a feature of the human diet since the time of the Neanderthals, but the mechanism by which this polysaccharide is broken down is unknown. In this work, the authors dissect the key processes and enzyme families in the gut that are involved in RG-II deconstruction. A single gut bacteria from the Bacteroides phylum metabolizes this complex substrate by cleaving all but one of the 21 glycosidic linkages. This degradation process involves seven newly discovered families of glycoside hydrolases, as well as novel catalytic functions of several known enzymes. This work delves deep into the mechanisms of glycan degradation by bacteria in the human gut microbiota and how they have evolved with this degradation to utilize rare sugars.
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