Zhou Yandong, Wang Xizhuo, Wang Xianming, Loktionova Natalia A, Cai Xiangyu, Nwokonko Robert M, Vrana Erin, Wang Youjun, Rothberg Brad S, Gill Donald L
Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Beijing Key Department of Genetics and Developmental Biology, College of Life Sciences, Beijing Normal University, Beijing 100875, China.
Nat Commun. 2015 Sep 24;6:8395. doi: 10.1038/ncomms9395.
The endoplasmic reticulum (ER) Ca(2+) sensor, STIM1, becomes activated when ER-stored Ca(2+) is depleted and translocates into ER-plasma membrane junctions where it tethers and activates Orai1 Ca(2+) entry channels. The dimeric STIM1 protein contains a small STIM-Orai-activating region (SOAR)--the minimal sequence sufficient to activate Orai1 channels. Since SOAR itself is a dimer, we constructed SOAR concatemer-dimers and introduced mutations at F394, which is critical for Orai1 coupling and activation. The F394H mutation in both SOAR monomers completely blocks dimer function, but F394H introduced in only one of the dimeric SOAR monomers has no effect on Orai1 binding or activation. This reveals an unexpected unimolecular coupling between STIM1 and Orai1 and argues against recent evidence suggesting dimeric interaction between STIM1 and two adjacent Orai1 channel subunits. The model predicts that STIM1 dimers may be involved in crosslinking between Orai1 channels with implications for the kinetics and localization of Orai1 channel opening.
内质网（ER）钙传感器STIM1在ER储存的钙耗尽时被激活，并转位至ER-质膜连接处，在那里它与Orai1钙进入通道结合并激活该通道。二聚体STIM1蛋白包含一个小的STIM-Orai激活区域（SOAR）——激活Orai1通道的最小序列。由于SOAR本身是一个二聚体，我们构建了SOAR串联二聚体，并在对Orai1偶联和激活至关重要的F394处引入突变。两个SOAR单体中的F394H突变完全阻断二聚体功能，但仅在二聚体SOAR单体之一中引入的F394H对Orai1结合或激活没有影响。这揭示了STIM1和Orai1之间意外的单分子偶联，并反驳了最近表明STIM1与两个相邻Orai1通道亚基之间存在二聚体相互作用的证据。该模型预测，STIM1二聚体可能参与Orai1通道之间的交联，这对Orai1通道开放的动力学和定位具有影响。
