1m01 | pdb_00001m01

Wildtype Streptomyces plicatus beta-hexosaminidase in complex with product (GlcNAc)

spinqualitylabelsall models 1m01, resolution 2.10Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 1m01 is a 1 chain structure with sequence from Atcc 25483. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Ligands: CL, GOL, NAG, SO4 Related: 1m03, 1m04, 1hp5, 1jak Activity: Beta-N-acetylhexosaminidase, with EC number 3.2.1.52 Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed SpHex, a retaining family 20 glycosidase from Streptomyces plicatus, catalyzes the hydrolysis of N-acetyl-beta-hexosaminides. Accumulating evidence suggests that the hydrolytic mechanism involves substrate-assisted catalysis wherein the 2-acetamido substituent acts as a nucleophile to form an oxazolinium ion intermediate. The role of a conserved aspartate residue (D313) in the active site of SpHex was investigated through kinetic and structural analyses of two variant enzymes, D313A and D313N. Three-dimensional structures of the wild-type and variant enzymes in product complexes with N-acetyl-d-glucosamine revealed substantial differences. In the D313A variant the 2-acetamido group was found in two conformations of which only one is able to aid in catalysis through anchimeric assistance. The mutation D313N results in a steric clash in the active site between Asn-313 and the 2-acetamido group preventing the 2-acetamido group from providing anchimeric assistance, consistent with the large reduction in catalytic efficiency and the insensitivity of this variant to chemical rescue. By comparison, the D313A mutation results in a shift in a shift in the pH optimum and a modest decrease in activity that can be rescued by using azide as an exogenous nucleophile. These structural and kinetic data provide evidence that Asp-313 stabilizes the transition states flanking the oxazoline intermediate and also assists to correctly orient the 2-acetamido group for catalysis. Based on analogous conserved residues in the family 18 chitinases and family 56 hyaluronidases, the roles played by the Asp-313 residue is likely general for all hexosaminidases using a mechanism involving substrate-assisted catalysis. Aspartate 313 in the Streptomyces plicatus hexosaminidase plays a critical role in substrate-assisted catalysis by orienting the 2-acetamido group and stabilizing the transition state.,Williams SJ, Mark BL, Vocadlo DJ, James MN, Withers SG J Biol Chem. 2002 Oct 18;277(42):40055-65. Epub 2002 Aug 8. PMID:12171933 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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