Molecular mechanism for structure-dependent ligand recognition of the hyaluronan receptor

透明质酸（HA）是一种非常简单的多糖，由重复的二糖单元组成，其中N-乙酰葡萄糖胺和葡萄糖醛酸通过交替的β-1，3和β-1，4键连接在一起。HA的简单重复结构涉及许多重要的细胞行为和组织结构的维持。HA的多种性质在很大程度上取决于其分子大小、组织浓度以及与结合分子的相互作用。在本研究中，我用扫描探针显微镜观察了HA的结构特征。HA的三维结构随其链长和浓度的变化而变化。为了研究HA结构在HA受体CD 44的配体识别中的重要性，我通过表面等离子体共振（SPR）分析了HA-CD 44相互作用的亲和力和动力学，发现HA结合分子versican增加了CD 44与HA的亲和力，表明versican通过改变HA结构来增强HA-CD 44相互作用。然后，我检查了HA结合分子SHAP对CD 44-HA相互作用介导的细胞粘附的影响。在静态和流动条件下，CD 44表达细胞粘附优先固定SHAP-HA复合物比单独的HA，表明SHAP通过增加HA对CD 44的亲合力来增强相互作用。

Hyaluronan (HA) is an extremely simple polysaccharide composed of repeating disaccharide units in which N-acetylglucosamine and glucuronic acid are linked together by alternating β-1,3 and β-1,4 linkages. The simple repeating structure of HA is involved in both a number of important cell behaviors and maintenance of tissue architecture. The multiple properties of HA depend largely on its molecular size, tissue concentration and the interaction with binding molecules. In this study, I examined the structural features of HA by scanning probe microscope. The three dimensional structure of HA changed dependently on its chain length and concentration. To examine the importance of HA structure in the ligand recognition of HA receptor CD44, I analyzed both affinity and kinetics of HA-CD44 interactions by surface plasmon resonance (SPR), and found that HA-binding molecule versican increased the affinity of CD44 to HA, suggesting that versican enhances the HA-CD44 interaction by altering HA structure. I then examined the effect of HA-binding molecule SHAP on the CD44-HA interaction-mediated cell adhesion. Under both static and flowing conditions, CD44-expressing cells adhered preferentially to the immobilized SHAP-HA complex than to HA alone, suggesting that SHAP enhances the interaction by increasing the avidity of HA to CD44.