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CRYSTAL STRUCTURE OF CHONDROITINASE B COMPLEXED TO CHONDROITIN 4-SULFATE TETRASACCHARIDE
Structural highlights
FunctionCSLB_PEDHD Cleaves the glycosaminoglycan, dermatan sulfate. 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 PubMedChondroitinase 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 structure of chondroitin B lyase complexed with glycosaminoglycan oligosaccharides unravels a calcium-dependent catalytic machinery.,Michel G, Pojasek K, Li Y, Sulea T, Linhardt RJ, Raman R, Prabhakar V, Sasisekharan R, Cygler M J Biol Chem. 2004 Jul 30;279(31):32882-96. Epub 2004 May 21. PMID:15155751[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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