Immune Disease Institute, Children's Hospital Boston and Department of Pathology, Harvard Medical School, Boston Massachusetts 02115; University Basel, PharmaCenter, Klingelbergstr. 50-70, 4056 Basel, Switzerland.
Immune Disease Institute, Children's Hospital Boston and Department of Pathology, Harvard Medical School, Boston Massachusetts 02115.
J Biol Chem. 2011 Dec 9;286(49):42115-42122. doi: 10.1074/jbc.M111.282830. Epub 2011 Sep 30.
The activation of α/β heterodimeric integrins is the result of highly coordinated rearrangements within both subunits. The molecular interactions between the two subunits, however, remain to be characterized. In this study, we use the integrin α(L)β(2) to investigate the functional role of the C-linker polypeptide that connects the C-terminal end of the inserted (I) domain with the β-propeller domain on the α subunit and is located at the interface with the βI domain of the β chain. We demonstrate that shortening of the C-linker by eight or more amino acids results in constitutively active α(L)β(2) in which the αI domain is no longer responsive to the regulation by the βI domain. Despite this intersubunit uncoupling, both I domains remain individually sensitive to intrasubunit conformational changes induced by allosteric modulators. Interestingly, the length and not the sequence of the C-linker appears to be critical for its functionality in α/β intersubunit communication. Using two monoclonal antibodies (R7.1 and CBR LFA-1/1) we further demonstrate that shortening of the C-linker results in the gradual loss of combinational epitopes that require both the αI and β-propeller domains for full reactivity. Taken together, our findings highlight the role of the C-linker as a spring-like element that allows relaxation of the αI domain in the resting state and controlled tension of the αI domain during activation, exerted by the β chain.
α/β 异源二聚体整合素的激活是两个亚基内部高度协调重排的结果。然而，两个亚基之间的分子相互作用仍有待表征。在这项研究中，我们使用整合素 α(L)β(2)来研究连接插入 (I) 结构域 C 端与 α 亚基 β 螺旋桨结构域的 C 链接多肽的功能作用，该结构域位于与 β 链的 βI 结构域的界面上。我们证明，C 链接缩短 8 个或更多氨基酸会导致 α(L)β(2)持续激活，其中 I 结构域不再响应 βI 结构域的调节。尽管这种亚基间解偶联，但两个 I 结构域仍然各自对别构调节剂诱导的亚基内构象变化敏感。有趣的是，C 链接的长度而不是序列对于其在 α/β 亚基间通讯中的功能似乎至关重要。使用两种单克隆抗体 (R7.1 和 CBR LFA-1/1)，我们进一步证明 C 链接的缩短导致需要 I 结构域和 β 螺旋桨结构域才能完全反应的组合表位的逐渐丧失。总之，我们的发现强调了 C 链接作为一个类似弹簧的元件的作用，它允许在静止状态下 I 结构域放松，并在激活期间由 β 链施加对 I 结构域的受控张力。
