| Summary: | <p>F<sub>1</sub>F<sub>o</sub> ATP synthase functions as a biological generator and makes a major contribution to cellular energy production. Proton flow generates rotation in the F<sub>o</sub> motor that is transferred to the F<sub>1</sub> motor to catalyze ATP production, with flexible F<sub>1</sub>/F<sub>o</sub> coupling required for efficient catalysis. F<sub>1</sub>F<sub>o</sub> ATP synthase can also operate in reverse, hydrolyzing ATP and pumping protons, and in bacteria this function can be regulated by an inhibitory ε subunit. Here we present cryo-EM data showing <em>E. coli</em> F<sub>1</sub>F<sub>o</sub> ATP synthase in different rotational and inhibited sub-states, observed following incubation with 10 mM MgATP. Our structures demonstrate how structural transitions within the inhibitory ε subunit induce torsional movement in the central stalk, thereby enabling its rotation within the F<sub>ο</sub> motor. This highlights the importance of the central rotor for flexible coupling of the F<sub>1</sub> and F<sub>o</sub> motors and provides further insight into the regulatory mechanism mediated by subunit ε.</p>
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