Assembly of human mitochondrial ATP synthase through two separate intermediates, F1-c-ring and b–e–g complex

•Two subcomplexes of human ATP synthase are formed in d-subunit deficient cells.•One contains a rotor shaft (F1-c-ring) and the other a stator stalk subunits (b–e–g).•F1-c-ring is also formed when Mt-DNA-coded a-subunit and A6L are deficient.•ATP synthase assembly from F1-c-ring and stator stalk may be common to all organisms. Mitochondrial ATP synthase is a motor enzyme in which a central shaft rotates in the stator casings fixed with the peripheral stator stalk. When expression of d-subunit, a stator stalk component, was knocked-down, human cells could not form ATP synthase holocomplex and instead accumulated two subcomplexes, one containing a central rotor shaft plus catalytic subunits (F1-c-ring) and the other containing stator stalk components (“b–e–g” complex). F1-c-ring was also formed when expression of mitochondrial DNA-coded a-subunit and A6L was suppressed. Thus, the central rotor shaft and the stator stalk are formed separately and they assemble later. Similar assembly strategy has been known for ATP synthase of yeast and Escherichia coli and could be common to all organisms.