The Biological Role of the ζ Subunit as Unidirectional Inhibitor of the F1FO-ATPase of Paracoccus denitrificans

Summary The biological roles of the three natural F 1 F O -ATPase inhibitors, e, ζ, and IF 1 , on cell physiology remain controversial. The ζ subunit is a useful model for deletion studies since it mimics mitochondrial IF 1 , but in the F 1 F O -ATPase of Paracoccus denitrificans (PdF 1 F O ), it is a monogenic and supernumerary subunit. Here, we constructed a P. denitrificans 1222 derivative (PdΔζ) with a deleted ζ gene to determine its role in cell growth and bioenergetics. The results show that the lack of ζ in vivo strongly restricts respiratory P. denitrificans growth, and this is restored by complementation in trans with an exogenous ζ gene. Removal of ζ increased the coupled PdF 1 F O -ATPase activity without affecting the PdF 1 F O -ATP synthase turnover, and the latter was not affected at all by ζ reconstitution in vitro . Therefore, ζ works as a unidirectional pawl-ratchet inhibitor of the PdF 1 F O -ATPase nanomotor favoring the ATP synthase turnover to improve respiratory cell growth and bioenergetics.