title: Structure and transport mechanism of the sodium/proton antiporter MjNhaP1.
abstract: Sodium/proton antiporters are essential for sodium and pH homeostasis and play a major role in human health and disease. We determined the structures of the archaeal sodium/proton antiporter MjNhaP1 in two complementary states. The inward-open state was obtained by x-ray crystallography in the presence of sodium at pH 8, where the transporter is highly active. The outward-open state was obtained by electron crystallography without sodium at pH 4, where MjNhaP1 is inactive. Comparison of both structures reveals a 7° tilt of the 6 helix bundle. (22)Na(+) uptake measurements indicate non-cooperative transport with an activity maximum at pH 7.5. We conclude that binding of a Na(+) ion from the outside induces helix movements that close the extracellular cavity, open the cytoplasmic funnel, and result in a ∼5 Å vertical relocation of the ion binding site to release the substrate ion into the cytoplasm.
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Cristina
authors.initials: C
authors.lastname: Paulino
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Wöhlert
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Kapotova
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Özkan
authors.initials: Ö
authors.lastname: Yildiz
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
mesh_terms: D002462:Cell Membrane / Q000737:chemistry; D018360:Crystallography, X-Ray; D063747:Methanocaldococcus / Q000378:metabolism*; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D021381:Protein Transport; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D013379:Substrate Specificity
chemical_list: D050505:Mutant Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium
keywords: Methanocaldococcus jannaschii; biochemistry; biophysics; electron cryo-microscopy; membrane transport; sodium/proton antiport; structural biology; transport mechanism; x-ray crystallography