Stator Structure and Subunit Composition of the V1/V0 Na+-ATPase of the Thermophilic Bacterium Caloramator fervidus

The V-type Na+-ATPase of the thermophilic, anaerobic bacterium Caloramator fervidus was purified to homogeneity. The subunit compositions of the catalytic V1 and membrane-embedded V0 parts were determined and the structure of the enzyme complex was studied by electron microscopy. The V1 headpiece consists of seven subunits present in one to three copies, and the V0 part of two subunits in a ratio of 5:2. An analysis of over 7500 single particle images obtained by electron microscopy of the purified V1V0 enzyme complex revealed that the stalk region, connecting the V1 and V0 parts, contains two peripheral stalks in addition to a central stalk. One of the two is connected to the V0 part, while the other is connected to the first via a bar-like structure that is positioned just above V0, parallel with the plane of the membrane. In projection, this bar seems to contact the central stalk. The data show that the stator structure that prevents rotation of the static part of V0 relative to V1 in the rotary catalysis mechanism of energy coupling in ATPases/ATPsynthases is more complex than previously thought.