title: Mechanics of coupling proton movements to c-ring rotation in ATP synthase.
abstract: F1F0 ATP synthases generate ATP by a rotary catalytic mechanism in which H+ transport is coupled to rotation of an oligomeric ring of c subunits extending through the membrane. Protons bind to and then are released from the aspartyl-61 residue of subunit c at the center of the membrane. Subunit a of the F0 sector is thought to provide proton access channels to and from aspartyl-61. Here, we summarize new information on the structural organization of Escherichia coli subunit a and the mapping of aqueous-accessible residues in the second, fourth and fifth transmembrane helices (TMHs). Aqueous-accessible regions of these helices extend to both the cytoplasmic and periplasmic surface. We propose that aTMH4 rotates to alternately expose the periplasmic or cytoplasmic half-channels to aspartyl-61 of subunit c during the proton transport cycle. The concerted rotation of interacting helices in subunit a and subunit c is proposed to be the mechanical force driving rotation of the c-rotor, using a mechanism akin to meshed gears.
authors: Department of Biomolecular Chemistry, 1300 University Avenue, University of Wisconsin Medical School, Madison, WI 53706, USA. rhfillin@facstaff.wisc.edu
authors: Robert H
authors: RH
authors: Fillingame
authors: Christine M
authors: CM
authors: Angevine
authors: Oleg Y
authors: OY
authors: Dmitriev
mesh_terms: D025243:Bacterial Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D018892:Proton-Motive Force; D012399:Rotation; D014867:Water / Q000737:chemistry
chemical_list: D021122:Protein Subunits; D014867:Water; D025243:Bacterial Proton-Translocating ATPases