Composition of the central stalk of the Na+-pumping V-ATPase from Caloramator fervidus

The Na⁺-pumping V-ATPase complex of the thermophilic bacterium Caloramator fervidus was purified and dissociated under controlled conditions. The structure of purified V₁-ATPase subcomplexes differing in subunit composition was analyzed by electron microscopy and single particle analysis of 50 000 projections. Difference mapping of subcomplex projections revealed the presence and position of two subunits in the central stalk. A density with an elongated shape similar to the γ subunit of F-ATPases is partly located within V₁ and corresponds, most likely, to subunit E. Subunit E is connected to the membrane-bound part V₀ via subunit C, a spherical density that is connected to the center of V₀. The presence of subunit C makes the central stalk substantially longer in comparison to the F-ATPases, in which the γ subunit connects directly to F₀.