Structural insights into human zinc transporter ZnT1 mediated Zn2+ efflux.

Zinc transporter 1 (ZnT1), the principal carrier of cytosolic zinc to the extracellular milieu, is important for cellular zinc homeostasis and resistance to zinc toxicity. Despite recent advancements in the structural characterization of various zinc transporters, the mechanism by which ZnTs-mediated Zn²⁺ translocation is coupled with H⁺ or Ca²⁺ remains unclear. To visualize the transport dynamics, we determined the cryo-electron microscopy (cryo-EM) structures of human ZnT1 at different functional states. ZnT1 dimerizes via extensive interactions between the cytosolic (CTD), the transmembrane (TMD), and the unique cysteine-rich extracellular (ECD) domains. At pH 7.5, both protomers adopt an outward-facing (OF) conformation, with Zn²⁺ ions coordinated at the TMD binding site by distinct compositions. At pH 6.0, ZnT1 complexed with Zn²⁺ exhibits various conformations [OF/OF, OF/IF (inward-facing), and IF/IF]. These conformational snapshots, together with biochemical investigation and molecular dynamic simulations, shed light on the mechanism underlying the proton-dependence of ZnT1 transport. Synopsis: ZnT1 is the major Zn²⁺ transporter expelling excessive Zn²⁺ ions out of cells. Distinct structural conformations of human ZnT1 captured by cryo-EM shed light on the intricate proton-driven transport mechanism. High-resolution cryo-EM structures of human ZnT1 were determined. Conformational dynamics of ZnT1 were captured in the presence of Zn²⁺ and low pH. Local changes between α-helix and 3₁₀ helix were observed in ZnT1 TM2 extracellular half. ZnT1 is the major Zn²⁺ transporter expelling excessive Zn²⁺ ions out of cells. Distinct structural conformations of human ZnT1 captured by cryo-EM shed light on the intricate proton-driven transport mechanism. [ABSTRACT FROM AUTHOR]