Correlation between the numbers of rotation steps in the ATPase and proton-conducting domains of F- and V-ATPases.

This letter reports the correlation in the number of distinct rotation steps between the F/V and F/V domains that constitute common rotary F- and V-ATP synthases/ATPases. Recent single-molecule studies on the F-ATPase revealed differences in the number of discrete steps in rotary catalysis between different organisms-6 steps per turn in bacterial types and mitochondrial F from yeast, and 9 steps in the mammalian mitochondrial F domains. The number of rotational steps that F domain makes is thought to correspond to that of proteolipid subunits within the rotating c-ring present in F. Structural studies on F and in the whole ATP synthase complex have shown a large diversity in the number of proteolipid subunits. Interestingly, 6 steps in F are always paired with 10 steps in F, whereas 9 steps in F are paired with 8 steps in F. The correlation in the number of steps has also been revealed for two types of V-ATPases: one having 6 steps in V paired with 10 steps in V, and the other one having 3 steps in V paired with 12 steps in V. Although the abovementioned correlations await further confirmation, the results suggest a clear trend; ATPase motors with more steps have proton-conducting motors with less steps. In addition, ATPases with 6 steps are always paired with proton-conducting domains with 10 steps.