6bs6
SusG with mixed linkage amylosaccharide
Structural highlights
FunctionSUSG_BACTN Alpha-amylase that cleaves starch into oligosaccharides before internalization for degradation, the first step in starch degradation.[1] [2] [3] Publication Abstract from PubMedBacteria that reside in the mammalian intestinal tract efficiently hydrolyze dietary carbohydrates, including starch, that escape digestion in the small intestine. Starch is an abundant dietary carbohydrate comprised of alpha1,4 and alpha1,6 linked glucose, yet mammalian intestinal glucoamylases cannot effectively hydrolyze starch that has frequent alpha1,6 branching as these structures hinder recognition and processing by alpha1,4-specific amylases. Here we present the structure of the cell surface amylase SusG from Bacteroides thetaiotaomicron complexed with a mixed linkage amylosaccharide generated from transglycosylation during crystallization. Although SusG is specific for alpha1,4 glucosidic bonds, binding of this new oligosaccharide at the active site demonstrates that SusG can accommodate alpha1,6 branch points at subsite -3 to -2, and also at subsite+1 adjacent to the site of hydrolysis, explaining how this enzyme may be able to process a wide range of limit dextrins in the intestinal environment. These data suggest that B. thetaiotaomicron and related organisms may have a selective advantage for amylosaccharide scavenging in the gut. Structural basis for the flexible recognition of alpha-glucan substrates by Bacteroides thetaiotaomicron SusG.,Arnal G, Cockburn DW, Brumer H, Koropatkin NM Protein Sci. 2018 Mar 30. doi: 10.1002/pro.3410. PMID:29603462[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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