Proton currents and protein motion in membranes

A mechanism is proposed whereby a proton gradient along a membrane-spanning alpha-helix is coupled to small changes in the torsional angles around the alpha-helix peptide bonds. Small concerted changes in the torsional angles are coupled to a change in the unit twist of the alpha-helix; a change in the unit twist is coupled to a change in the crossing angle between neighbouring alpha-helices; and a change in the crossing angle is coupled to a change in the size and shape of an assembly of alpha-helices. Following this logical linkage in one direction shows how a proton gradient could induce a pumping motion in an assembly of alpha-helices; following it in the other direction shows how motion in an assembly of alpha-helices could pump protons.