Division of Signaling and Gene Expression, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA.
Division of Signaling and Gene Expression, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA; Program in Immunology, University of California, San Diego, La Jolla, CA 92037, USA.
Cell Rep. 2018 Jan 2;22(1):72-83. doi: 10.1016/j.celrep.2017.12.030.
STIM1 and STIM2 are endoplasmic reticulum (ER) membrane proteins that sense decreases in ER-luminal free Ca and, through a conformational change in the STIM cytoplasmic domain, control gating of the plasma membrane Ca channel ORAI1. To determine how STIM1 conveys a signal from the ER lumen to the cytoplasm, we studied the Ca-dependent conformational change of engineered STIM1 proteins in isolated ER membranes and, in parallel, physiological activation of these proteins in cells. We find that conserved "sentinel" features of the CC1 region help to prevent activation while Ca is bound to STIM ER-luminal domains. Reduced ER-luminal Ca drives a concerted conformational change, in which STIM luminal domains rearrange and the STIM transmembrane helices and initial parts of the CC1 regions pair in an extended coiled coil. This intradimer rearrangement overcomes the relatively weak CC1-SOAR/CAD interactions that hold STIM in an inactive conformation, releasing the SOAR/CAD domain to activate ORAI channels.
STIM1 和 STIM2 是内质网（ER）膜蛋白，可感知 ER 腔游离 Ca 的减少，并通过 STIM 细胞质结构域的构象变化，控制质膜 Ca 通道 ORAI1 的门控。为了确定 STIM1 如何将信号从 ER 腔传递到细胞质，我们研究了在分离的 ER 膜中工程化的 STIM1 蛋白的 Ca 依赖性构象变化，并在细胞中对这些蛋白进行了生理激活。我们发现 CC1 区域的保守“哨兵”特征有助于在 Ca 结合到 STIM ER 腔域时防止激活。减少 ER 腔 Ca 驱动协同构象变化，其中 STIM 腔域重新排列，STIM 跨膜螺旋和 CC1 区域的初始部分在延伸的卷曲螺旋中配对。这种二聚体内部重排克服了将 STIM 保持在非活性构象的相对较弱的 CC1-SOAR/CAD 相互作用，释放 SOAR/CAD 结构域以激活 ORAI 通道。
