Membrane-bound Vo/Ao complexes of V/A-type ATP synthases, subunit c
Vo/Ao-ATP synthase subunit c. The V- and A-type family of ATPases are composed of two linked multi-subunit complexes: the V1 and A1 complexes contain three copies each of the alpha and beta subunits that form the soluble catalytic core, which is involved in ATP synthesis/hydrolysis, and the Vo or Ao complex that forms the membrane-embedded proton pore. The A-ATP synthase (AoA1-ATPases) is exclusively found in archaea and functions like the F-ATP synthase. Structurally, however, the A-ATP synthase is more closely related to the V-ATP synthase (vacuolar VoV1-ATPase), which is a proton-translocating ATPase responsible for acidification of eukaryotic intracellular compartments and for ATP synthesis in archaea and some eubacteria. The V- and A-type synthases can function in both ATP synthesis and hydrolysis modes. The V1 complex consists of three A and three B subunits, two G subunits plus the C, D, E, F, and H subunits. The Vo complex consists of five different subunits: a, c, c', c'', and d. The Ao/A1 complexes are composed of nine subunits in a stoichiometry of A(3):B(3):C:D:E:F:H(2):a:c(x). ATP is synthesized on the A3:B3 hexamer and the energy released during that process is transferred to the Ao complex, which consists of the C-terminal segment of subunit a and subunit c.
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