Structures of Heparin-Derived Disaccharide Bound to Cobra Cardiotoxins: Context-Dependent Conformational Change of Heparin upon Binding to the Rigid Core of the Three-Fingered Toxin

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• 作者：Shih-Che Sue ; Jean-Robert Brisson ; Siu-Cin Chang ; Wei-Ning Huang ; Shao-Chen Lee ; Harold C. Jarrell ; and Wen-guey Wu
• 刊名：Biochemistry
• 出版年：2001
• 出版时间：September 4, 2001
• 年：2001
• 卷：40
• 期：35
• 页码：10436 - 10446
• 全文大小：430K
• 年卷期：v.40,no.35(September 4, 2001)
• ISSN：1520-4995

文摘

Glycosaminoglycans (GAGs) have been suggested to be a potential target for cobra cardiotoxin(CTX) with high affinity and specificity via a cationic belt at the concave surface of the polypeptide. Theinteraction of GAGs, such as high-molecular weight heparin, with CTXs not only can induce aggregationof CTX molecules but also can enhance their penetration into membranes. The binding of short chainheparin, such as a heparin-derived disaccharide [UA2S(14)--D-GlcNS6S], to CTX A3 from Taiwancobra (Naja atra), however, will not induce aggregation and was, therefore, investigated by high-resolution¹H NMR. A novel heparin binding site on the convex side of the CTX, near the rigid disulfide bond-tightened core region of Cys38, was identified due to the observation of intermolecular NOEs betweenthe protein and carbohydrate. The derived carbohydrate conformation using complete relaxation andconformational exchange matrix analysis (CORCEMA) of NOEs indicated that the glycosidic linkageconformation and the ring conformation of the unsaturated uronic acid in the bound state dependedsignificantly on the charge context of CTX molecules near the binding site. Specifically, comparativebinding studies of several heparin disaccharide homologues with two CTX homologues (CTX T fromNaja nigricollis and CTX A3) indicated that the electrostatic interaction of N-sulfate of glucosamine withNH₃⁺ of Lys12 and of the 2-O-sulfate of the unsaturated uronic acid with NH₃⁺ of Lys5 played animportant role. These results also suggest a model on how the CTX-heparin interaction may regulateheparin-induced aggregation of the toxin via the second heparin binding site.