Aerobic Growth of Escherichia coli Is Reduced, and ATP Synthesis Is Selectively Inhibited when Five C-terminal Residues Are Deleted from the ε Subunit of ATP Synthase

F-type ATP synthases are rotary nanomotor enzymes involved in cellular energy metabolism in eukaryotes and eubacteria. The ATP synthase from Gram-positive and -negative model bacteria can be autoinhibited by the C-terminal domain of its epsilon subunit (epsilon TD), but the importance of epsilon inhibition in vivo is unclear. Functional rotation is thought to be blocked by insertion of the latter half of the epsilon CTD into the central cavity of the catalytic complex (F1). In the inhibited state of the Escherichia coli enzyme, the final segment of epsilon CTD is deeply buried but has few specific interactions with other subunits. This region of the epsilon CTD is variable or absent in other bacteria that exhibit strong epsilon-inhibition in vitro. Here, genetically deleting the last five residues of the epsilon CTD (epsilon Delta 5) caused a greater defect in respiratory growth than did the complete absence of the epsilon CTD. Isolated membranes with epsilon Delta 5 generated proton-motive force by respiration as effectively as with wild-type epsilon but showed a nearly 3-fold decrease in ATP synthesis rate. In contrast, the epsilon Delta 5 truncation did not change the intrinsic rate of ATP hydrolysis with membranes. Further, the epsilon Delta 5 subunit retained high affinity for isolated F-1 but reduced the maximal inhibition of F-1-ATPase by epsilon from >90% to similar to 20%. The results suggest that the epsilon CTD has distinct regulatory interactions with F1 when rotary catalysis operates in opposite directions for the hydrolysis or synthesis of ATP.