Essential arginine in subunit a and aspartate in subunit c of F0F1 ATP synthase -: Effect of repositioning within Helix 4 of subunit a and Helix 2 of subunit c

FoF1 ATP synthase couples proton flow through the integral membrane portion F-o (ab(2)c(10)) to ATP-synthesis in the extrinsic F-1-part ((alpha beta)(3)gamma delta epsilon) (Escherichia coli nomenclature and stoichiometry). Coupling occurs by mechanical rotation of subunits c(10)gamma epsilon relative to (alpha beta)(3)delta ab(2). Two residues were found to be essential for proton flow through ab(2)c(10), namely Arg(210) in subunit a (aR210) and Asp(61) in subunits c (cD61). Their deletion abolishes proton flow, but horizontal repositioning, by anchoring them in adjacent transmembrane helices, restores function. Here, we investigated the effects of vertical repositioning aR210, cD61, or both by one helical turn towards the N- or C-termini of their original helices. Other than in the horizontal the vertical displacement changes the positions of the side chains within the depth of the membrane. Mutant aR210A/ aN214R appeared to be short-circuited in that it supported proton conduction only through EF1-depleted EFo, but not in EFoEF1, nor ATP-driven proton pumping. Mutant cD61N/cM65D grew on succinate, retained the ability to synthesize ATP and supported passive proton conduction but apparently not ATP hydrolysis-driven proton pumping. (C) 2007 Elsevier B.V. All rights reserved.