Molecular architecture of the undecameric rotor of a bacterial Na+-ATP synthase

J Mol Biol. 2002 Aug 9;321(2):307-16. doi: 10.1016/s0022-2836(02)00597-1.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacteria / enzymology*
  • Binding Sites
  • Conserved Sequence
  • Cryoelectron Microscopy*
  • Cytoplasm / metabolism
  • Ions / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Phospholipids / metabolism
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Protein Subunits
  • Proton-Translocating ATPases / chemistry*
  • Proton-Translocating ATPases / metabolism
  • Proton-Translocating ATPases / ultrastructure*
  • Sodium / metabolism

Substances

  • Ions
  • Phospholipids
  • Protein Subunits
  • Sodium
  • Proton-Translocating ATPases