Plant cells have specific organelle distinct from moving animals, vacuoles, which store toxic chemicals such as ferric ions. Vacuolar iron transporter 1 (VIT1) transports cytoplasmic ferric ions into vacuoles. We solved crystal structure of VIT1, which acts as an H+-dependent antiporter for Fe2+ and other transition metal ions. VIT1 adopts a novel protein fold forming a dimer of five-membrane-spanning domains, forming an ion-translocating pathway constituted by the conserved methionine and carboxylate residues at the dimer interface. The second transmembrane helix protrudes from the lipid membrane by about 40 Å and forms a three-helical-bundle triangular cytoplasmic domain, which binds to the substrate metal ions and stabilizes their soluble form, thus playing an essential role in the transport.
Recent progress in cryo-EM single particle analysis enables us to solve large membrane protein structure rapidly. I would like to present here new structures of heterodimeric amino-acid transporter and two physical stimuli-sensing channels from human to uncover their molecular mechanisms.