INA complex liaises the F1Fo-ATP synthase membrane motor modules - Ina22-Flag pulldown experiments

The F1Fo-ATP synthase translates a proton flux across the inner mitochondrial membrane into a mechanical rotation, driving anhydride bond formation in the catalytic portion. The complex's membrane-embedded motor section forms a proteinaceous channel at the interface between Atp9 ring and Atp6. To prevent unrestricted proton flow dissipating the H+-gradient, channel formation is a critical and tightly controlled step during ATP synthase assembly. Here we show that the INA complex (INAC) acts at this decisive step promoting Atp9 ring association with Atp6. INAC binds initially to newly synthesized mitochondrial-encoded Atp6 and Atp8 in complex with maturation factors. INAC association is retained until the F1-portion is built on Atp6/8 and loss of INAC causes accumulation of the free F1. An independent complex is formed between INAC and the Atp9 ring. We conclude that INAC maintains assembly intermediates of the F1Fo-ATP synthase in a primed state for the terminal assembly step – channel and motor module formation.