ATP synthase, alpha/beta subunits of F1/V1/A1 complex, flagellum-specific ATPase FliI, N-terminal domain
The alpha and beta (or A and B) subunits are primarily found in the F1, V1, and A1 complexes of the F-, V- and A-type family of ATPases with rotary motors. These ion-transporting rotary ATPases are composed of two linked multi-subunit complexes: the F1, V1, or A1 complex which contains three copies each of the alpha and beta subunits that form the soluble catalytic core involved in ATP synthesis/hydrolysis, and the Fo, Vo, or Ao complex which forms the membrane-embedded proton pore. The F-ATP synthases (also called FoF1-ATPases) are found in the inner membranes of eukaryotic mitochondria, in the thylakoid membranes of chloroplasts, or in the plasma membranes of bacteria. F-ATPases are the primary producers of ATP, using the proton gradient generated by oxidative phosphorylation (mitochondria) or photosynthesis (chloroplasts). Alternatively, under conditions of low driving force, ATP synthases function as ATPases, thus generating a transmembrane proton or Na(+) gradient at the expense of energy derived from ATP hydrolysis. The A-ATP synthases (AoA1-ATPases), a different class of proton-translocating ATP synthases, are found in archaea and function like F-ATP synthases. Structurally, however, the A-ATP synthases are more closely related to the V-ATP synthases (vacuolar VoV1-ATPases), which are a proton-translocating ATPase responsible for acidification of eukaryotic intracellular compartments and for ATP synthesis in archaea and some eubacteria. Collectively, F-, V-, and A-type synthases can function in both ATP synthesis and hydrolysis modes. This family also includes the flagellum-specific ATPase/type III secretory pathway virulence-related protein, which shows extensive similarity to the alpha and beta subunits of F1-ATP synthase.
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