Department of Chemistry, National Tsing Hua University, 30013 Hsinchu, Taiwan.
Department of Chemistry, National Tsing Hua University, 30013 Hsinchu, Taiwan
Proc Natl Acad Sci U S A. 2020 Dec 1;117(48):30126-30134. doi: 10.1073/pnas.2014094117. Epub 2020 Nov 18.
BsYetJ is a bacterial homolog of transmembrane BAX inhibitor-1 motif-containing 6 (TMBIM6) membrane protein that plays a key role in the control of calcium homeostasis. However, the BsYetJ (or TMBIM6) structure embedded in a lipid bilayer is uncharacterized, let alone the molecular mechanism of the calcium transport activity. Herein, we report structures of BsYetJ in lipid nanodiscs identified by double electron-electron resonance spectroscopy. Our results reveal that BsYetJ in lipid nanodiscs is structurally different from those crystallized in detergents. We show that BsYetJ conformation is pH-sensitive in apo state (lacking calcium), whereas in a calcium-containing solution it is stuck in an intermediate, inert to pH changes. Only when the transmembrane calcium gradient is established can the calcium-release activity of holo-BsYetJ occur and be mediated by pH-dependent conformational changes, suggesting a dual gating mechanism. Conformational substates involved in the process and a key residue D171 relevant to the gating of calcium are identified. Our study suggests that BsYetJ/TMBIM6 is a pH-dependent, voltage-gated calcium channel.
BsYetJ 是一种细菌同源物，是跨膜 BAX 抑制剂-1 基序包含 6（TMBIM6）膜蛋白，在钙稳态的控制中起着关键作用。然而，嵌入脂质双层中的 BsYetJ（或 TMBIM6）结构尚未确定，更不用说钙转运活性的分子机制了。在此，我们通过双电子-电子共振光谱报道了在脂质纳米盘中鉴定出的 BsYetJ 结构。我们的结果表明，脂质纳米盘中的 BsYetJ 结构与在去污剂中结晶的结构不同。我们表明，BsYetJ 构象在 apo 状态（缺乏钙）下对 pH 敏感，而在含有钙的溶液中，它会卡在中间状态，对 pH 变化不敏感。只有当建立跨膜钙梯度时，全钙 BsYetJ 的钙释放活性才能发生，并由 pH 依赖性构象变化介导，这表明存在双重门控机制。确定了参与该过程的构象亚基和与钙门控相关的关键残基 D171。我们的研究表明，BsYetJ/TMBIM6 是一种 pH 依赖性、电压门控钙通道。
