Bacterial Na+‐ATP synthase has an undecameric rotor

Abstract
Synthesis of adenosine triphosphate (ATP) by the F1F ATP synthase involves a membrane‐embedded rotary engine, the F domain, which drives the extra‐membranous catalytic F1 domain. The F domain consists of subunits a 1 b 2 and a cylindrical rotor assembled from 9–14 α‐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.