Structural basis for molecular mechanisms of novel membrane transporters and channels

Abstract

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.