Structure of the zinc transporter YiiP

YiiP is a membrane transporter that catalyzes Zn²⁺/H⁺ exchange across the inner membrane of Escherichia coli. Mammalian homologs of YiiP play critical roles in zinc homeostasis and cell signaling. Here, we report the x-ray structure of YiiP in complex with zinc at 3.8 angstrom resolution. YiiP is a homodimer held together in a parallel orientation through four Zn ²⁺ ions at the interface of the cytoplasmic domains, whereas the two transmembrane domains swing out to yield a Y-shaped structure. In each protomer, the cytoplasmic domain adopts a metallochaperone-like protein fold; the transmembrane domain features a bundle of six transmembrane helices and a tetrahedral Zn²⁺ binding site located in a cavity that is open to both the membrane outer leaflet and the periplasm.