Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
J Cell Biol. 2013 Jul 8;202(1):71-9. doi: 10.1083/jcb.201301148. Epub 2013 Jul 1.
Ca(2+) influx by store-operated Ca(2+) channels (SOCs) mediates all Ca(2+)-dependent cell functions, but excess Ca(2+) influx is highly toxic. The molecular components of SOC are the pore-forming Orai1 channel and the endoplasmic reticulum Ca(2+) sensor STIM1. Slow Ca(2+)-dependent inactivation (SCDI) of Orai1 guards against cell damage, but its molecular mechanism is unknown. Here, we used homology modeling to identify a conserved STIM1(448-530) C-terminal inhibitory domain (CTID), whose deletion resulted in spontaneous clustering of STIM1 and full activation of Orai1 in the absence of store depletion. CTID regulated SCDI by determining access to and interaction of the STIM1 inhibitor SARAF with STIM1 Orai1 activation region (SOAR), the STIM1 domain that activates Orai1. CTID had two lobes, STIM1(448-490) and STIM1(490-530), with distinct roles in mediating access of SARAF to SOAR. The STIM1(448-490) lobe restricted, whereas the STIM1(490-530) lobe directed, SARAF to SOAR. The two lobes cooperated to determine the features of SCDI. These findings highlight the central role of STIM1 in SCDI and provide a molecular mechanism for SCDI of Orai1.
钙（Ca2+）内流通过由储存操作的 Ca2+ 通道（SOC）介导所有依赖 Ca2+的细胞功能，但过多的 Ca2+内流是高度毒性的。SOC 的分子组成部分是形成孔的 Orai1 通道和内质网 Ca2+传感器 STIM1。Orai1 的缓慢 Ca2+依赖性失活（SCDI）可防止细胞损伤，但它的分子机制尚不清楚。在这里，我们使用同源建模来识别保守的 STIM1（448-530）C 末端抑制结构域（CTID），其缺失导致 STIM1 的自发聚集和 Orai1 的完全激活，而无需储存耗尽。CTID 通过确定 STIM1 抑制剂 SARAF 与 STIM1 Orai1 激活区域（SOAR）的接触和相互作用来调节 SCDI，STIM1 是激活 Orai1 的结构域。CTID 有两个叶，STIM1（448-490）和 STIM1（490-530），在介导 SARAF 与 SOAR 的接触方面具有不同的作用。STIM1（448-490）叶限制，而 STIM1（490-530）叶引导 SARAF 至 SOAR。两个叶共同决定 SCDI 的特征。这些发现突出了 STIM1 在 SCDI 中的核心作用，并为 Orai1 的 SCDI 提供了分子机制。
