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.
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.
复制标题
与眼镜蛇心脏毒素结合的肝素衍生二糖的结构：与三指毒素的刚性核心结合后肝素的背景依赖性构象变化。
作者：
S. Sue;J. Brisson;S. C. Chang;W. N. Huang;S. C. Lee;H. Jarrell;W. Wu
糖胺聚糖（Glycosaminoglycans，GAG）是眼镜蛇心脏毒素（cobra cardiotoxin，CTX）的潜在靶点，具有高亲和力和特异性，可通过多肽凹面的阳离子带作用。GAG如高分子量肝素与CTX的相互作用不仅可以诱导CTX分子的聚集，而且可以增强其渗透到膜中。然而，短链肝素，如肝素衍生的二糖[Δ UA 2S（1->4）-α-D-GlcNS 6S]与来自台湾眼镜蛇（Naja atra）的CTX A3的结合不会诱导聚集，因此通过高分辨率（1）H NMR研究。由于观察到蛋白质和碳水化合物之间的分子间NOE，在CTX的凸面上，靠近Cys 38的刚性二硫键收紧的核心区域，鉴定了一个新的肝素结合位点。NOE的完全松弛和构象交换矩阵分析（CORCEMA）表明，糖链构象和糖醛酸环构象在结合态下明显依赖于CTX分子结合位点附近的电荷背景。具体而言，几种肝素二糖同系物与两种CTX同系物（来自Naja nigricollis的CTX Tgamma和CTX A3）的比较结合研究表明，葡萄糖胺的N-硫酸盐与Lys 12的NH（3）（+）zeta以及不饱和糖醛酸的2-O-硫酸盐与Lys 5的NH（3）（+）zeta的静电相互作用起着重要作用。这些结果还表明了CTX-肝素相互作用如何通过第二个肝素结合位点调节肝素诱导的毒素聚集的模型。
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. The interaction of GAGs, such as high-molecular weight heparin, with CTXs not only can induce aggregation of CTX molecules but also can enhance their penetration into membranes. The binding of short chain heparin, such as a heparin-derived disaccharide [DeltaUA2S(1-->4)-alpha-D-GlcNS6S], to CTX A3 from Taiwan cobra (Naja atra), however, will not induce aggregation and was, therefore, investigated by high-resolution (1)H 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 between the protein and carbohydrate. The derived carbohydrate conformation using complete relaxation and conformational exchange matrix analysis (CORCEMA) of NOEs indicated that the glycosidic linkage conformation and the ring conformation of the unsaturated uronic acid in the bound state depended significantly on the charge context of CTX molecules near the binding site. Specifically, comparative binding studies of several heparin disaccharide homologues with two CTX homologues (CTX Tgamma from Naja nigricollis and CTX A3) indicated that the electrostatic interaction of N-sulfate of glucosamine with NH(3)(+)zeta of Lys12 and of the 2-O-sulfate of the unsaturated uronic acid with NH(3)(+)zeta of Lys5 played an important role. These results also suggest a model on how the CTX-heparin interaction may regulate heparin-induced aggregation of the toxin via the second heparin binding site.