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717 a.a.
_CA
Key reference
DOI no: 10.1074/jbc.M806115200 J Biol Chem 283:36328-36337 (2008) PubMed id: 18981178
Structural and Functional Analysis of a Glycoside Hydrolase Family 97 Enzyme from Bacteroides thetaiotaomicron. M.Kitamura, M.Okuyama, F.Tanzawa, H.Mori, Y.Kitago, N.Watanabe, A.Kimura, I.Tanaka, M.Yao. ABSTRACT
SusB, an 84-kDa alpha-glucoside hydrolase involved in the starch utilization system (sus) of Bacteroides thetaiotaomicron, belongs to glycoside hydrolase (GH) family 97. We have determined the enzymatic characteristics and the crystal structures in free and acarbose-bound form at 1.6A resolution. SusB hydrolyzes the alpha-glucosidic linkage, with inversion of anomeric configuration liberating the beta-anomer of glucose as the reaction product. The substrate specificity of SusB, hydrolyzing not only alpha-1,4-glucosidic linkages but also alpha-1,6-, alpha-1,3-, and alpha-1,2-glucosidic linkages, is clearly different from other well known glucoamylases belonging to GH15. The structure of SusB was solved by the single-wavelength anomalous diffraction method with sulfur atoms as anomalous scatterers using an in-house x-ray source. SusB includes three domains as follows: the N-terminal, catalytic, and C-terminal domains. The structure of the SusB-acarbose complex shows a constellation of carboxyl groups at the catalytic center; Glu(532) is positioned to provide protonic assistance to leaving group departure, with Glu(439) and Glu(508) both positioned to provide base-catalyzed assistance for inverting nucleophilic attack by water. A structural comparison with other glycoside hydrolases revealed significant similarity between the catalytic domain of SusB and those of alpha-retaining glycoside hydrolases belonging to GH27, -36, and -31 despite the differences in catalytic mechanism. SusB and the other retaining enzymes appear to have diverged from a common ancestor and individually acquired the functional carboxyl groups during the process of evolution. Furthermore, sequence comparison of the active site based on the structure of SusB indicated that GH97 included both retaining and inverting enzymes.
Literature references that cite this PDB file's key reference
PubMed id Reference
19553672 E.C.Martens, N.M.Koropatkin, T.J.Smith, and J.I.Gordon (2009).
Complex glycan catabolism by the human gut microbiota: the Bacteroidetes Sus-like paradigm.J Biol Chem, 284, 24673-24677. The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time.
