State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, China ; College of Life Sciences, Nankai University, Tianjin, China.
PLoS One. 2013 Sep 19;8(9):e74735. doi: 10.1371/journal.pone.0074735. eCollection 2013.
Store-operated Ca(2+) entry (SOCE) is a critical Ca(2+) signaling pathway in many cell types. After sensing Ca(2+) store depletion in the endoplasmic reticulum (ER) lumen, STIM1 (STromal Interaction Molecule 1) oligomerizes and then interacts with and activates the Orai1 calcium channel. Our previous research has demonstrated that the inhibitory helix (IH) adjacent to the first coiled-coil region (CC1) of STIM1 may keep the whole C-terminus of STIM1 in an inactive state. However, the specific conformational change of CC1-IH that drives the transition of STIM1 from the resting state to the active state remains elusive. Herein, we report the structural analysis of CC1-IH, which revealed that the entire CC1-IH molecule forms a very long helix. Structural and biochemical analyses indicated that IH, and not the CC1 region, contributes to the oligomerization of STIM1. Small-angle X-ray scattering (SAXS) analysis suggested that the C-terminus of STIM1 including the IH region displays a collapsed conformation, whereas the construct without the IH region has an extended conformation. These two conformations may correspond to the conformational states of the C-terminus of STIM1 before and after activation. Taken together, our results provide direct biochemical evidence that the IH region controls the conformational switching of the C-terminus of STIM1.
钙库操纵性钙内流（SOCE）是许多细胞类型中一种关键的钙信号通路。内质网（ER）腔中钙库耗竭后，STIM1（基质相互作用分子 1）寡聚化，然后与 Orai1 钙通道相互作用并激活该通道。我们之前的研究表明，STIM1 第一个卷曲螺旋区（CC1）附近的抑制螺旋（IH）可能使 STIM1 的整个 C 端处于非活性状态。然而，驱动 STIM1 从静息状态向激活状态转变的 CC1-IH 的具体构象变化仍然难以捉摸。在此，我们报告了 CC1-IH 的结构分析，结果表明整个 CC1-IH 分子形成了一个非常长的螺旋。结构和生化分析表明，IH 而不是 CC1 区域，有助于 STIM1 的寡聚化。小角 X 射线散射（SAXS）分析表明，包括 IH 区域的 STIM1 C 端呈现出塌陷构象，而没有 IH 区域的构建体则呈现出伸展构象。这两种构象可能分别对应于 STIM1 C 端在激活前后的构象状态。总之，我们的结果提供了直接的生化证据，表明 IH 区域控制着 STIM1 C 端的构象转换。
