Coupling proton movements to c-ring rotation in F(1)F(o) ATP synthase: aqueous access channels and helix rotations at the a-c interface.
F(1)F(o) ATP synthases generate ATP by a rotary catalytic mechanism in which H(+) transport is coupled to rotation of a ring of c subunits within the transmembrane sector of the enzyme. Protons bind to and then are released from the aspartyl-61 residue of subunit c at the center of the membrane. Proton access channels to and from aspartyl-61 are thought to form in subunit a of the F(o) sector. Here, we summarize new information on the structural organization of subunit a and the mapping of aqueous accessible residues in the fourth and fifth transmembrane helices (TMHs). Cysteine substituted residues, lying on opposite faces of aTMH-4, preferentially react with either N-ethyl-maleimide (NEM) or Ag(+). We propose that aTMH-4 rotates to alternately expose each helical face to aspartyl-61 of subunit c during the proton transport cycle. The concerted helical rotation of aTMH-4 and cTMH-2 are proposed to be coupled to the stepwise mechanical movement of the c-rotor.
Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison 53706-1532, USA. rhfillin@facstaff.wisc.edu
Robert H
RH
Fillingame
Christine M
CM
Angevine
Oleg Y
OY
Dmitriev
D020346:Aquaporins / Q000737:chemistry*; D004926:Escherichia coli; D005033:Ethylmaleimide; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D020409:Molecular Motor Proteins; D015394:Molecular Structure; D006180:Proton-Translocating ATPases / Q000737:chemistry*; D011522:Protons; D012399:Rotation
D020346:Aquaporins; D020409:Molecular Motor Proteins; D011522:Protons; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide