Structural investigations of the membrane-embedded rotor ring of the F-ATPase from Clostridium paradoxum

The Na+-translocating F-ATPase of the thermoalkaliphilic bacterium Clostridium paradoxum harbors an oligomeric ring of c subunits that resists dissociation by sodium dodecyl sulfate. The c ring has been isolated and crystallized in two dimensions. From electron microscopy of these c-ring crystals, a projection map was calculated to 7 angstrom resolution. In the projection map, each c ring consists of two concentric, slightly staggered, packed rings, each composed of 11 densities representing the alpha-helices. On the basis of these results, it was determined that the F-ATPase from C paradoxum contains an undecameric c ring.