title: Molecular architecture of the undecameric rotor of a bacterial Na+-ATP synthase.
abstract: The sodium ion-translocating F(1)F(0) ATP synthase from the bacterium Ilyobacter tartaricus contains a remarkably stable rotor ring composed of 11 c subunits. The rotor ring was isolated, crystallised in two dimensions and analysed by electron cryo-microscopy. Here, we present an alpha-carbon model of the c-subunit ring. Each monomeric c subunit of 89 amino acid residues folds into a helical hairpin consisting of two membrane-spanning helices and a cytoplasmic loop. The 11 N-terminal helices are closely spaced within an inner ring surrounding a cavity of approximately 17A (1.7 nm). The tight helix packing leaves no space for side-chains and is accounted for by a highly conserved motif of four glycine residues in the inner, N-terminal helix. Each inner helix is connected by a clearly visible loop to an outer C-terminal helix. The outer helix has a kink near the position of the ion-binding site residue Glu65 in the centre of the membrane and another kink near the C terminus. Two helices from the outer ring and one from the inner ring form the ion-binding site in the middle of the membrane and a potential access channel from the binding site to the cytoplasmic surface. Three possible inter-subunit ion-bridges are likely to account for the remarkable temperature stability of I.tartaricus c-rings compared to those of other organisms.
authors.affiliation: Max-Planck-Institute of Biophysics, Heinrich-Hoffmann-Str. 7, Frankfurt, Germany.
authors.forename: Janet
authors.initials: J
authors.lastname: Vonck
authors.forename: Tassilo Krug
authors.initials: TK
authors.lastname: von Nidda
authors.forename: Thomas
authors.initials: T
authors.lastname: Meier
authors.forename: Ulrich
authors.initials: U
authors.lastname: Matthey
authors.forename: Deryck J
authors.initials: DJ
authors.lastname: Mills
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Peter
authors.initials: P
authors.lastname: Dimroth
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology*; D001665:Binding Sites; D017124:Conserved Sequence; D020285:Cryoelectron Microscopy; D003593:Cytoplasm / Q000378:metabolism; D007477:Ions / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D012964:Sodium / Q000378:metabolism
chemical_list: D007477:Ions; D010743:Phospholipids; D021122:Protein Subunits; D012964:Sodium; D006180:Proton-Translocating ATPases