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| {{STRUCTURE_1ofm| PDB=1ofm | SCENE= }} | | {{STRUCTURE_1ofm| PDB=1ofm | SCENE= }} |
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| '''CRYSTAL STRUCTURE OF CHONDROITINASE B COMPLEXED TO CHONDROITIN 4-SULFATE TETRASACCHARIDE'''
| | ===CRYSTAL STRUCTURE OF CHONDROITINASE B COMPLEXED TO CHONDROITIN 4-SULFATE TETRASACCHARIDE=== |
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| ==Overview==
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| Chondroitinase B from Pedobacter heparinus is the only known enzyme strictly specific for dermatan sulfate and is a widely used enzymatic tool for the structural characterization of glycosaminoglycans. This beta-helical polysaccharide lyase belongs to family PL-6 and cleaves the beta(1,4) linkage of dermatan sulfate in a random manner, yielding 4,5-unsaturated dermatan sulfate disaccharides as the product. The previously reported structure of its complex with a dermatan sulfate disaccharide product identified the -1 and -2 subsites of the catalytic groove. We present here the structure of chondroitinase B complexed with several dermatan sulfate and chondroitin sulfate oligosaccharides. In particular, the soaking of chondroitinase B crystals with a dermatan sulfate hexasaccharide results in a complex with two dermatan sulfate disaccharide reaction products, enabling the identification of the +2 and +1 subsites. Unexpectedly, this structure revealed the presence of a calcium ion coordinated by sequence-conserved acidic residues and by the carboxyl group of the l-iduronic acid at the +1 subsite. Kinetic and site-directed mutagenesis experiments have subsequently demonstrated that chondroitinase B absolutely requires calcium for its activity, indicating that the protein-Ca(2+)-oligosaccharide complex is functionally relevant. Modeling of an intact tetrasaccharide in the active site of chondroitinase B provided a better understanding of substrate specificity and the role of Ca(2+) in enzymatic activity. Given these results, we propose that the Ca(2+) ion neutralizes the carboxyl moiety of the l-iduronic acid at the cleavage site, whereas the conserved residues Lys-250 and Arg-271 act as Bronsted base and acid, respectively, in the lytic degradation of dermatan sulfate by chondroitinase B.
| | The line below this paragraph, {{ABSTRACT_PUBMED_15155751}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 15155751 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_15155751}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Chondroitin 4-sulfate]] | | [[Category: Chondroitin 4-sulfate]] |
| [[Category: Lyase]] | | [[Category: Lyase]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 03:47:15 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 29 03:56:12 2008'' |
