Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
J Biol Chem. 2011 Apr 8;286(14):12086-92. doi: 10.1074/jbc.M110.208900. Epub 2011 Feb 4.
Lymphocyte homing is regulated by the dynamic interaction between integrins and their ligands. Integrin α4β7 mediates both rolling and firm adhesion of lymphocytes by modulating its affinity to the ligand, mucosal addressin cell adhesion molecule-1 (MAdCAM-1). Although previous studies have revealed some mechanisms of α4β7-MAdCAM-1 binding, little is known about the different molecular bases of the low- and high-affinity α4β7-MAdCAM-1 interactions, which mediate rolling and firm adhesion of lymphocytes, respectively. Here, we found that two loops in immunoglobulin domains 1 and 2 (D1 and D2) of MAdCAM-1 played different roles in MAdCAM-1 binding to low-affinity (inactive) and high-affinity (activated) α4β7. The Asp-42 in the CC' loop of D1 was indispensable for MAdCAM-1 binding to both low-affinity and high-affinity α4β7. The other CC' loop residues except for Arg-39 and Ser-44 were essential for MAdCAM-1 binding to both inactive α4β7 and α4β7 activated by SDF-1α or talin, but not required for MAdCAM-1 binding to Mn2+-activated α4β7. Single amino acid substitution of the DE loop residues mildly decreased MAdCAM-1 binding to both inactive and activated α4β7. Notably, removal of the DE loop greatly impaired MAdCAM-1 binding to inactive and SDF-1α- or talin-activated α4β7, but only decreased 60% of MAdCAM-1 binding to Mn2+-activated α4β7. Moreover, DE loop residues were important for stabilizing the low-affinity α4β7-MAdCAM-1 interaction. Thus, our findings demonstrate the distinct roles of the CC' and DE loops in the recognition of MAdCAM-1 by low- and high-affinity α4β7 and suggest that the inactive α4β7 and α4β7 activated by different stimuli have distinct conformations with different structural requirements for MAdCAM-1 binding.
淋巴细胞归巢受整合素与其配体之间动态相互作用的调节。整合素 α4β7 通过调节其与配体黏膜地址素细胞黏附分子-1（MAdCAM-1）的亲和力，介导淋巴细胞的滚动和牢固黏附。虽然先前的研究已经揭示了 α4β7-MAdCAM-1 结合的一些机制，但对于介导淋巴细胞滚动和牢固黏附的低亲和力和高亲和力 α4β7-MAdCAM-1 相互作用的不同分子基础知之甚少。在这里，我们发现 MAdCAM-1 的免疫球蛋白结构域 1 和 2（D1 和 D2）中的两个环在 MAdCAM-1 与低亲和力（无活性）和高亲和力（激活）α4β7 的结合中发挥不同的作用。D1 中的 CC'环中的天冬氨酸 42 对于 MAdCAM-1 与低亲和力和高亲和力 α4β7 的结合都是必不可少的。除精氨酸 39 和丝氨酸 44 以外的其他 CC'环残基对于 MAdCAM-1 与无活性的α4β7 和由 SDF-1α 或 talin 激活的α4β7 的结合都是必需的，但对于 MAdCAM-1 与 Mn2+-激活的 α4β7 的结合则不是必需的。DE 环残基的单个氨基酸取代轻度降低了 MAdCAM-1 与无活性和激活的α4β7 的结合。值得注意的是，DE 环的缺失大大损害了 MAdCAM-1 与无活性和 SDF-1α 或 talin 激活的α4β7 的结合，但仅降低了 60%与 Mn2+-激活的α4β7 的结合。此外，DE 环残基对于稳定低亲和力α4β7-MAdCAM-1 相互作用很重要。因此，我们的发现表明 CC'和 DE 环在低亲和力和高亲和力 α4β7 识别 MAdCAM-1 方面的不同作用，并表明不同刺激激活的无活性的α4β7 和α4β7 具有不同的构象，对于 MAdCAM-1 的结合具有不同的结构要求。
