Binding of Phytopolyphenol Piceatannol Disrupts β/γ Subunit Interactions and Rate-limiting Step of Steady-state Rotational Catalysis in Escherichia coli F1-ATPase

In observations of single molecule behavior under V-max conditions with minimal load, the F-1 sector of the ATP synthase (F-ATPase) rotates through continuous cycles of catalytic dwells (similar to 0.2 ms) and 120 degrees rotation steps (similar to 0.6 ms). We previously established that the rate-limiting transition step occurs during the catalytic dwell at the initiation of the 120 degrees rotation. Here, we use the phytopolyphenol, piceatannol, which binds to a pocket formed by contributions from alpha and beta stator subunits and the carboxyl-terminal region of the rotor gamma subunit. Piceatannol did not interfere with the movement through the 120 degrees rotation step, but caused increased duration of the catalytic dwell. The duration time of the intrinsic inhibited state of F-1 also became significantly longer with piceatannol. All of the beads rotated at a lower rate in the presence of saturating piceatannol, indicating that the inhibitor stays bound throughout the rotational catalytic cycle. The Arrhenius plot of the temperature dependence of the reciprocal of the duration of the catalytic dwell (catalytic rate) indicated significantly increased activation energy of the rate-limiting step to trigger the 120 degrees rotation. The activation energy was further increased by combination of piceatannol and substitution of gamma subunit Met(23) with Lys, indicating that the inhibitor and the beta/gamma interface mutation affect the same transition step, even though they perturb physically separated rotor-stator interactions.