Salt-overly-sensitive 1 (SOS1) is a unique electroneutral Na⁺/H⁺ antiporter at the plasma membrane of higher plants and plays a central role in resisting salt stress. SOS1 is kept in a resting state with basal activity and activated upon phosphorylation. Here, we report the structures of SOS1. SOS1 forms a homodimer, with each monomer composed of transmembrane and intracellular domains. We find that SOS1 is locked in an occluded state by shifting of the lateral-gate TM5b toward the dimerization domain, thus shielding the Na⁺/H⁺ binding site. We speculate that the dimerization of the intracellular domain is crucial to stabilize the transporter in this specific conformation. Moreover, two discrete fragments and a residue W1013 are important to prevent the transition of SOS1 to an alternative conformational state, as validated by functional complementation assays. Our study enriches understanding of the alternate access model of eukaryotic Na⁺/H⁺ exchangers.

盐过度敏感1（SOS1）是高等植物质膜上独特的电中性Na ⁺ /H ^{+逆向转运蛋白，在抵抗盐胁迫中发挥着核心作用。}SOS1 保持在具有基础活性的静息状态，并在磷酸化后被激活。在这里，我们报告了 SOS1 的结构。SOS1 形成同型二聚体，每个单体由跨膜结构域和细胞内结构域组成。我们发现，SOS1 通过将侧门 TM5b 移向二聚化结构域而锁定在封闭状态，从而屏蔽 Na ⁺ /H ⁺结合位点。我们推测细胞内结构域的二聚化对于稳定转运蛋白在这种特定构象中至关重要。此外，两个离散片段和一个残基 W1013 对于防止 SOS1 转变为替代构象状态非常重要，这一点已通过功能互补测定进行验证。^{我们的研究丰富了对真核Na +} /H ⁺交换器交替访问模型的理解。