ATP binding to the ε subunit of thermophilic ATP synthase is crucial for efficient coupling of ATPase and H+ pump activities

ATP binding to the a subunit of F-1-ATPase, a soluble subcomplex of TF0F1 (F0F1-ATPase synthase from the thermophilic Bacillus strain PS3), affects the regulation of F-1-ATPase activity by stabilizing the compact, ATPase-active, form of the epsilon subunit [Kato, S., Yoshida, M. and Kato-Yamada, Y. (2007) J. Biol. Chem. 282, 37618-37623]. In the present study, we report how ATP binding to the epsilon subunit affects ATPase and H+ pumping activities in the holoenzyme TF0F1. Wild-type TF0F1, showed significant H+ pumping activity when ATP was used as the substrate. However, GTP, which bound poorly to the epsilon subunit, did not support efficient H+ pumping. Addition of small amounts of ATP to the GTP substrate restored coupling between GTPase and H+ pumping activities. Similar uncoupling was observed when TF0F1, contained an ATP-binding-deficient epsilon subunit, even with ATP as a substrate. Further analysis suggested that the compact conformation of the a subunit induced by ATP binding was required to couple ATPase and H+ pumping activities in TF0F1 unless the epsilon subunit was in its extended-state conformation. The present study reveals a novel role of the epsilon subunit as an ATPsensitive regulator of the coupling of ATPase and H+ pumping activities of TF0F1.