Bacterial Na+-ATP synthase has an undecameric rotor

Synthesis of adenosine triphosphate (ATP) by the F1F0 ATP synthase involves a membrane-embedded rotary engine, the F-0 domain, which drives the extra-membranous catalytic F-1 domain. The F-0 domain consists of subunits a(1)b(2) and a cylindrical rotor assembled from 9-14 alpha -helical hairpin-shaped c-subunits. According to structural analyses, rotors contain 10 c-subunits in yeast and 14 in chloroplast ATP synthases. We determined the rotor stoichiometry of Ilyobacter tartaricus ATP synthase by atomic force microscopy and cryo-electron microscopy, and show the cylindrical sodium-driven rotor to comprise 11 c-subunits.