Salas Azucena, Shimaoka Motomu, Phan Uyen, Kim Minsoo, Springer Timothy A
CBR Institute for Biomedical Research, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 2006 Apr 21;281(16):10876-82. doi: 10.1074/jbc.M512472200. Epub 2006 Feb 27.
AlphaLbeta2 affinity for intercellular adhesion molecule-1 (ICAM-1) is regulated by the conformation of the alphaL I domain, which is in turn controlled by the conformation and orientation of other adjacent domains. Additionally, overall integrin conformation (bent versus straightened) influences the orientation of the I domain and access to its ligands, influencing adhesive efficiency. The open or high affinity I domain conformation supports strong adhesion, whereas the closed, low affinity conformation mediates weak interactions or rolling. We have previously suggested that alphaLbeta2 can also exist on the cell surface in an intermediate affinity state. Here we have studied the adhesive properties of integrin alphaLbeta2 containing mutant I domains with intermediate affinities for ICAM-1. In an overall bent conformation, the intermediate affinity state of alphaLbeta2 is hardly detected by conventional adhesion assays, but robust adhesion is seen when an extended conformation is induced by a small molecule alpha/beta I allosteric antagonist. Intermediate affinity alphaLbeta2 supports more stable rolling than wild-type alphaLbeta2 under shear conditions. Moreover, antagonist-induced extension transforms rolling adhesion into firm adhesion in a manner reminiscent of chemokine activation of integrin alphaLbeta2. These findings suggest the relevance of intermediate affinity states of alphaLbeta2 to the transition between inactive and active states and demonstrate the importance of both I domain affinity and overall integrin conformation for cell adhesion.
αLβ2对细胞间黏附分子-1（ICAM-1）的亲和力受αL I结构域构象的调节，而αL I结构域的构象又受其他相邻结构域的构象和取向控制。此外，整合素的整体构象（弯曲与伸直）会影响I结构域的取向及其与配体的结合，进而影响黏附效率。开放或高亲和力的I结构域构象支持强黏附，而封闭的低亲和力构象介导弱相互作用或滚动。我们之前曾提出αLβ2也可以以中等亲和力状态存在于细胞表面。在此，我们研究了含有对ICAM-1具有中等亲和力的突变I结构域的整合素αLβ2的黏附特性。在整体弯曲构象下，传统黏附试验几乎检测不到αLβ2的中等亲和力状态，但当小分子α/β I变构拮抗剂诱导其伸展构象时，可观察到强大的黏附。在剪切条件下，中等亲和力的αLβ2比野生型αLβ2支持更稳定的滚动。此外，拮抗剂诱导的伸展以类似于趋化因子激活整合素αLβ2的方式将滚动黏附转变为牢固黏附。这些发现表明αLβ2的中等亲和力状态与非活性和活性状态之间的转变相关，并证明了I结构域亲和力和整合素整体构象对细胞黏附的重要性。
