Structural evidence for a constant c11 ring stoichiometry in the sodium F-ATP synthase.

The Na+-dependent F-ATP synthases of Ilyobacter tartaricus and Propionigenium modestum contain membrane-embedded ring-shaped c subunit assemblies with a stoichiometry of 11. Subunit c from either organism was overexpressed in Escherichia coli using a plasmid containing the corresponding gene, extracted from the membrane using detergent and then purified. Subsequent analyses by SDS/PAGE revealed that only a minor portion of the c subunits had assembled into stable rings, while the majority migrated as monomers.

The central plug in the reconstituted undecameric c cylinder of a bacterial ATP synthase consists of phospholipids.

The isolated rotor cylinder of the ATP synthase from Ilyobacter tartaricus was reconstituted into two-dimensional crystalline arrays. Atomic force microscopy imaging indicated a central cavity on one side of the rotor and a central plug protruding from the other side. Upon incubation with phospholipase C, the plug disappeared, but the appearance of the surrounding c subunit oligomer was not affected.