Half channels mediating H(+) transport and the mechanism of gating in the Fo sector of Escherichia coli F1Fo ATP synthase.

Abstract H + -transporting F 1 F o ATP synthase catalyzes the synthesis of ATP via coupled rotary motors within F o and F 1 . H + transport at the subunit a–c interface in trans-membranous F o drives rotation of the c -ring within the membrane, with subunit c being bound in a complex with the γ and e subunits extending from the membrane. Finally, the rotation of subunit γ within the α 3 β 3 sector of F 1 mechanically drives ATP synthesis within the catalytic sites. In this review, we propose and provide evidence supporting the route of proton transfer via half channels from one side of the membrane to the other, and the mechanism of gating H + binding to and release from Asp61 of subunit c , via conformational movements of Arg210 in subunit a . We propose that protons are gated from the inside of a four-helix bundle at the periplasmic side of subunit a to drive protonation of c Asp61, and that this gating movement is facilitated by the swiveling of trans-membrane helices (TMHs) 4 and 5 at the site of interaction with c Asp61 on the periphery of the c -ring. Proton release to the cytoplasmic half channel is facilitated by the movement of a Arg210 as a consequence of this proposed helical swiveling. Finally, release from the cytoplasmic half channel is mediated by residues in a complex of interacting extra-membraneous loops formed between TMHs of both subunits a and c . This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.