1hp4
From Proteopedia
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CRYSTAL STRUCTURE OF STREPTOMYCES PLICATUS BETA-N-ACETYLHEXOSAMINIDASE
Overview
beta-Hexosaminidase, a family 20 glycosyl hydrolase, catalyzes the removal, of beta-1,4-linked N-acetylhexosamine residues from oligosaccharides and, their conjugates. Heritable deficiency of this enzyme results in various, forms of GalNAc-beta(1,4)-[N-acetylneuraminic acid, (2,3)]-Gal-beta(1,4)-Glc-ceramide gangliosidosis, including Tay-Sachs, disease. We have determined the x-ray crystal structure of a, beta-hexosaminidase from Streptomyces plicatus to 2.2 A resolution, (Protein Data Bank code ). beta-Hexosaminidases are believed to use a, substrate-assisted catalytic mechanism that generates a cyclic oxazolinium, ion intermediate. We have solved and refined a complex between the cyclic, intermediate analogue N-acetylglucosamine-thiazoline and, beta-hexosaminidase from S. plicatus to 2.1 A resolution (Protein Data, Bank code ). Difference Fourier analysis revealed the pyranose ring of, N-acetylglucosamine-thiazoline bound in the enzyme active site with a, conformation close to that of a (4)C(1) chair. A tryptophan-lined, hydrophobic pocket envelopes the thiazoline ring, protecting it from, solvolysis at the iminium ion carbon. Within this pocket, Tyr(393) and, Asp(313) appear important for positioning the 2-acetamido group of the, substrate for nucleophilic attack at the anomeric center and for, dispersing the positive charge distributed into the oxazolinium ring upon, cyclization. This complex provides decisive structural evidence for, substrate-assisted catalysis and the formation of a covalent, cyclic, intermediate in family 20 beta-hexosaminidases.
About this Structure
1HP4 is a Single protein structure of sequence from Streptomyces plicatus with CL, SO4 and GOL as ligands. Active as Beta-N-acetylhexosaminidase, with EC number 3.2.1.52 Full crystallographic information is available from OCA.
Reference
Crystallographic evidence for substrate-assisted catalysis in a bacterial beta-hexosaminidase., Mark BL, Vocadlo DJ, Knapp S, Triggs-Raine BL, Withers SG, James MN, J Biol Chem. 2001 Mar 30;276(13):10330-7. Epub 2000 Dec 21. PMID:11124970
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