Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland.
Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland.
J Biol Chem. 2022 Mar;298(3):101607. doi: 10.1016/j.jbc.2022.101607. Epub 2022 Jan 20.
The stromal interaction molecule 1 (STIM1) is an endoplasmic reticulum (ER) Ca sensor that regulates the activity of Orai plasma membrane Ca channels to mediate the store-operated Ca entry pathway essential for immunity. Uncoordinated 93 homolog B1 (UNC93B1) is a multiple membrane-spanning ER protein that acts as a trafficking chaperone by guiding nucleic-acid sensing toll-like receptors to their respective endosomal signaling compartments. We previously showed that UNC93B1 interacts with STIM1 to promote antigen cross-presentation in dendritic cells, but the STIM1 binding site(s) and activation step(s) impacted by this interaction remained unknown. In this study, we show that UNC93B1 interacts with STIM1 in the ER lumen by binding to residues in close proximity to the transmembrane domain. Cysteine crosslinking in vivo showed that UNC93B1 binding promotes the zipping of transmembrane and proximal cytosolic helices within resting STIM1 dimers, priming STIM1 for translocation. In addition, we show that UNC93B1 deficiency reduces store-operated Ca entry and STIM1-Orai1 interactions and targets STIM1 to lighter ER domains, whereas UNC93B1 expression accelerates the recruitment of STIM1 to cortical ER domains. We conclude that UNC93B1 therefore acts as a trafficking chaperone by maintaining the pool of resting STIM1 proteins in a state primed for activation, enabling their rapid translocation in an extended conformation to cortical ER signaling compartments.
基质相互作用分子 1（STIM1）是内质网（ER）Ca 传感器，调节 Orai 质膜 Ca 通道的活性，介导必需的储存操作 Ca 进入途径，该途径对免疫至关重要。未协调的 93 同源物 B1（UNC93B1）是一种具有多个跨膜结构域的内质网蛋白，作为一种运输伴侣，通过引导核酸感应 Toll 样受体进入各自的内体信号隔室来发挥作用。我们之前表明 UNC93B1 与 STIM1 相互作用，以促进树突状细胞中的抗原交叉呈递，但这种相互作用影响的 STIM1 结合位点（s）和激活步骤（s）仍然未知。在这项研究中，我们表明 UNC93B1 通过与靠近跨膜域的残基结合，在 ER 腔中与 STIM1 相互作用。体内半胱氨酸交联表明，UNC93B1 结合促进了静止 STIM1 二聚体中跨膜和近细胞质螺旋的拉链，为 STIM1 的易位做好准备。此外，我们表明 UNC93B1 缺乏会减少储存操作 Ca 进入和 STIM1-Orai1 相互作用，并将 STIM1 靶向较轻的 ER 域，而 UNC93B1 表达加速了 STIM1 向皮质 ER 域的募集。我们得出结论，UNC93B1 因此作为一种运输伴侣，通过将静止 STIM1 蛋白的池保持在激活的预备状态来发挥作用，使它们能够快速易位到皮质 ER 信号隔室中，并保持延伸构象。
