Studies on molecular analysis of cell adhesion mediated by carbohydrate recognitions

选择素是一个碳水化合物结合蛋白家族（c型凝集素），参与白细胞运输、血栓形成、炎症、肿瘤转移等。在本研究中，我们利用合成的sialyl Lewis X和多种类似物，不仅在分子水平上，而且在官能团水平上证明了选择素介导细胞粘附的机制。结果表明：(1)唾液酸Lewis X表位与e -选择素相互作用的结合面，唾液酸的羧基、半乳糖的4-羟基和6-羟基以及焦点的2-、3-和4-羟基参与了选择素与碳水化合物的结合，并且焦点部分直接参与了钙依赖；(2)通过与硫脂的比较，强烈地提出了羧基和硫酸盐基团的作用，以及作为对应物的碱性氨基酸的存在；(3)作为本研究结果中最重要的发现，首次全合成了硫酸化的sialyl Lewis X五糖神经节苷，揭示了人l -选择素与6-0-sulfo（在GlcNAc部分）sialyl Lewis X的结合要比sialyl Lewis X强得多，提示了硫酸化盖层控制受体特异性的可能性。此外，由于6'- o磺化（在Gal部分），e -选择素的结合丢失。所有这些结果都是世界上第一次发现。另一方面，在一系列澄清唾液粘附素家族（i型凝集素）识别特异性的研究中，我们已经证明神经节苷脂GQ1balpha是髓鞘相关糖蛋白（MAG）结合最强的碳水化合物配体之一。

The selectins are a family of carbohydrate-binding proteins (C-type lectin) involved in leukocyte trafficking, thrombosis, inflammation, tumor metastasis, and so on. In this study, we have demonstrated the mechanism of cell adhesion mediated by selectins not only on the molecular level but also on the level of functional groups by using synthetic sialyl Lewis X and a variety of the analogs. As a result, it has been concluded that : (1) For the binding face of the sialyl Lewis X epitope interacting with E-selectin, the carboxyl group of sialic acid, the 4- and 6-hydroxyls of galactose, and the 2-, 3-, and 4-hydroxyls of fucose are involved in selectin-carbohydrate binding, and further, the fucose moiety is directly involved in the calcium dependency ; (2) Based on the comparison with sulfatide, the roles of carboxyl and sulfate groups, and the presence of the basic amino acids as the counterparts have strongly been suggested ; (3) As the most important finding of the current results, the first total syntheses of the sulfated sialyl Lewis X pentasaccharide gangliosides revealed that the binding of human L-selectin to the 6-0-sulfo (in the GlcNAc moiety) sialyl Lewis X is much stronger than that of sialyl Lewis X,suggesting the possibility of the receptor specificity control by sulfation cappings. In addition, the binding of E-selectin was lost by the 6'-O-sulafation (in the Gal moiety). All these results are the first findings in the world.On the other hand, in a series of studies on clarifying the recognition specificity of sialoadhesin family (I-type lectin), we have demonstrated that ganglioside GQ1balpha is one of the strongest carbohydrate ligands for the binding of myelin-associated glycoprotein (MAG).