Effects of iodide on the coupling between ATP hydrolysis and motile activity in axonemal dynein

Dynein transduces the chemical energy of ATP hydrolysis into mechanical work through conformational changes. To identify the factors governing the coupling between the ATPase activity and the motile activity of the dynein molecule, we examined the effects of potassium iodide, which can unfold protein tertiary structures, on dynein activity in reactivated sea urchin sperm flagella. The presence of low concentrations of KI (0.05-0.1 M) in the reactivating solution did not influence the stable beating of demembranated flagella at 0.02-1 mM ATP, when the total concentration of potassium was kept at 0.15 M by adding K-acetate. However, double-reciprocal plots of ATP concentration and beat frequency showed a mixed type of inhibition by KI, indicating the possibility that KI inhibits the ATP hydrolysis and decreases the maximum sliding velocity. The ATPase activity of 21S dynein with or without microtubules did not decrease with the KI concentration. In the elastase-treated axonemes, KI decreased the velocity of sliding disintegration, while it increased the frequency of occurrence of axonemes showing no sliding. This may be related to some defect in the coordination of dynein activities. On 21S dynein adsorbed on a glass surface, however, the velocity of microtubule sliding was increased by KI, while KI lowered the dynein-microtubule affinity. The velocity further increased under lower salt conditions enhancing the dynein-microtubule interactions. The results suggest the importance of organized regulation of the dynamic states of dynein-microtubule interactions through the stalk for the coupling between the ATPase activity and the motile activity of dynein in beating flagella.