Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
Sci Adv. 2017 Aug 25;3(8):e1700344. doi: 10.1126/sciadv.1700344. eCollection 2017 Aug.
Zrt/Irt-like proteins (ZIPs) play fundamental roles in metal metabolism/homeostasis and are broadly involved in numerous physiological and pathological processes. The lack of high-resolution structure of the ZIPs hinders understanding of the metal transport mechanism. We report two crystal structures of a prokaryotic ZIP in lipidic cubic phase with bound metal substrates (Cd at 2.7 Å and Zn at 2.4 Å). The structures revealed a novel 3+2+3TM architecture and an inward-open conformation occluded at the extracellular side. Two metal ions were trapped halfway through the membrane, unexpectedly forming a binuclear metal center. The Zn-substituted structure suggested asymmetric functions of the two metal-binding sites and also revealed a route for zinc release. Mapping of disease-causing mutations, structure-guided mutagenesis, and cell-based zinc transport assay demonstrated the crucial role of the binuclear metal center for human ZIP4. A metal transport mechanism for the ZIP from was proposed, which is likely applicable to other ZIPs.
Zrt/Irt 样蛋白（ZIPs）在金属代谢和稳态中发挥着基本作用，并广泛参与许多生理和病理过程。由于缺乏 ZIPs 的高分辨率结构，阻碍了对金属转运机制的理解。我们报告了两种带有结合金属底物（Cd 为 2.7Å，Zn 为 2.4Å）的类脂立方相中的原核 ZIP 的晶体结构。这些结构揭示了一种新颖的 3+2+3TM 架构和一种在细胞外被阻断的内开构象。两个金属离子被卡在膜中间，出乎意料地形成了双核金属中心。Zn 取代结构表明两个金属结合位点的功能不对称，并揭示了锌释放的途径。疾病相关突变的定位、结构指导的突变和基于细胞的锌转运测定表明，双核金属中心对人 ZIP4 至关重要。提出了一种用于 ZIP 的金属转运机制，该机制可能适用于其他 ZIP。
