Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA.
Institute of Biosciences and Technology, College of Medicine, Texas A&M University, Houston, TX, 77030, USA.
Nat Commun. 2023 Oct 30;14(1):6921. doi: 10.1038/s41467-023-42254-x.
Ca signal-generation through inter-membrane junctional coupling between endoplasmic reticulum (ER) STIM proteins and plasma membrane (PM) Orai channels, remains a vital but undefined mechanism. We identify two unusual overlapping Phe-His aromatic pairs within the STIM1 apical helix, one of which (F394-H398) mediates important control over Orai1-STIM1 coupling. In resting STIM1, this locus is deeply clamped within the folded STIM1-CC1 helices, likely near to the ER surface. The clamped environment in holo-STIM1 is critical-positive charge replacing Phe-394 constitutively unclamps STIM1, mimicking store-depletion, negative charge irreversibly locks the clamped-state. In store-activated, unclamped STIM1, Phe-394 mediates binding to the Orai1 channel, but His-398 is indispensable for transducing STIM1-binding into Orai1 channel-gating, and is spatially aligned with Phe-394 in the exposed Sα2 helical apex. Thus, the Phe-His locus traverses between ER and PM surfaces and is decisive in the two critical STIM1 functions-unclamping to activate STIM1, and conformational-coupling to gate the Orai1 channel.
内质网 (ER) STIM 蛋白与质膜 (PM) Orai 通道之间的膜间连接偶联产生钙信号，这仍然是一个重要但尚未确定的机制。我们在 STIM1 顶端螺旋中发现了两个不寻常的重叠苯丙氨酸-组氨酸芳香对，其中一个（F394-H398）对 Orai1-STIM1 偶联具有重要的控制作用。在静息 STIM1 中，该位置被深深地夹在折叠的 STIM1-CC1 螺旋内，可能靠近 ER 表面。完整 STIM1 中的夹闭环境是关键的——正电荷取代苯丙氨酸 394 会使 STIM1 持续解夹，模拟储存耗竭，负电荷会不可逆地锁定夹闭状态。在储存激活、解夹的 STIM1 中，苯丙氨酸 394 介导与 Orai1 通道的结合，但组氨酸 398 对于将 STIM1 结合转化为 Orai1 通道门控是不可或缺的，并且与暴露的 Sα2 螺旋顶端的苯丙氨酸 394 在空间上对齐。因此，苯丙氨酸-组氨酸位点在 ER 和 PM 表面之间穿梭，并且在两个关键的 STIM1 功能中是决定性的——解夹以激活 STIM1，以及构象偶联以门控 Orai1 通道。
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