1hp5: Difference between revisions

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[[Image:1hp5.jpg|left|200px]]
{{Seed}}
[[Image:1hp5.png|left|200px]]


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{{STRUCTURE_1hp5|  PDB=1hp5  |  SCENE=  }}  
{{STRUCTURE_1hp5|  PDB=1hp5  |  SCENE=  }}  


'''STREPTOMYCES PLICATUS BETA-N-ACETYLHEXOSAMINIDASE COMPLEXED WITH INTERMEDIATE ANALOUGE NAG-THIAZOLINE'''
===STREPTOMYCES PLICATUS BETA-N-ACETYLHEXOSAMINIDASE COMPLEXED WITH INTERMEDIATE ANALOUGE NAG-THIAZOLINE===




==Overview==
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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.
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{{ABSTRACT_PUBMED_11124970}}


==About this Structure==
==About this Structure==
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[[Category: Substrate assisted catalysis]]
[[Category: Substrate assisted catalysis]]
[[Category: Tim barrel]]
[[Category: Tim barrel]]
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 19:05:16 2008''
 
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 08:29:37 2008''

Revision as of 05:29, 1 July 2008

File:1hp5.png

Template:STRUCTURE 1hp5

STREPTOMYCES PLICATUS BETA-N-ACETYLHEXOSAMINIDASE COMPLEXED WITH INTERMEDIATE ANALOUGE NAG-THIAZOLINE

Template:ABSTRACT PUBMED 11124970

About this Structure

1HP5 is a Single protein structure of sequence from Streptomyces plicatus. 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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