Inorganic phosphate (Pi) is a fundamental macronutrient for all living organisms, the homeostasis of which is critical for numerous biological activities^1,2,3. As the only known human Pi exporter to date, XPR1 has an indispensable role in cellular Pi homeostasis^4,5. Dysfunction of XPR1 is associated with neurodegenerative disease^6,7,8. However, the mechanisms underpinning XPR1-mediated Pi efflux and regulation by the intracellular inositol polyphosphate (InsPP) sensor SPX domain remain poorly understood. Here we present cryo-electron microscopy structures of human XPR1 in Pi-bound closed, open and InsP₆-bound forms, revealing the structural basis for XPR1 gating and regulation by InsPPs. XPR1 consists of an N-terminal SPX domain, a dimer-formation core domain and a Pi transport domain. Within the transport domain, three basic clusters are responsible for Pi binding and transport, and a conserved W573 acts as a molecular switch for gating. In addition, the SPX domain binds to InsP₆ and facilitates Pi efflux by liberating the C-terminal loop that limits Pi entry. This study provides a conceptual framework for the mechanistic understanding of Pi homeostasis by XPR1 homologues in fungi, plants and animals.

无机磷酸盐 （Pi） 是所有生物体的基本常量营养素，其稳态对许多生物活动至关重要^1,2,3。作为迄今为止唯一已知的人类 Pi 输出因子，XPR1 在细胞 Pi 稳态中发挥着不可或缺的作用^4,5。XPR1 功能障碍与神经退行性疾病有关^6,7,8。然而，支持 XPR1 介导的 Pi 外排和细胞内肌醇多磷酸盐 （InsPP） 传感器 SPX 结构域的调节机制仍然知之甚少。在这里，我们以 Pi 结合、封闭、开放和 InsP₆ 结合的形式展示了人 XPR1 的冷冻电子显微镜结构，揭示了 InsPPs 对 XPR1 门控和调节的结构基础。XPR1 由一个 N 末端 SPX 结构域、一个二聚体形成核心结构域和一个 Pi 转运结构域组成。在转运结构域中，三个基本簇负责 Pi 结合和转运，保守的 W573 充当门控的分子开关。此外，SPX 结构域与 InsP₆ 结合，并通过释放限制 Pi 进入的 C 端环来促进 Pi 外排。本研究为真菌、植物和动物中 XPR1 同源物对 Pi 稳态的机制理解提供了一个概念框架。