cAMP-stimulated phosphorylation of an axonemal polypeptide that copurifies with the 22S dynein arm regulates microtubule translocation velocity and swimming speed in Paramecium

In Paramecium tetraurelia, cyclic nucleotides are important physiological second messengers that could regulate dynein mechanochemistry by phosphorylation. A 29-kDa polypeptide that is phosphorylated in a cAMP- and Ca²⁺-sensitive manner in permeabilized cells and isolated axonemes is the only significant phosphorylated moiety that consistently copurifies with 22S dynein from paramecium cilia. It is not a component of 14S dynein. This polypeptide can be thiophosphorylated in a cAMP-sensitive manner, and this form of 22S dynein is stable when stored at -70°C. cAMP-mediated thiophosphorylation of the 29-kDa polypeptide significantly increases the velocity with which 22S dynein causes microtubules to glide in vitro. The increase is abolished, together with the thiophosphorylation of the 29-kDa polypeptide, by preincubation with high Ca²⁺. Pretreatment with high Ca²⁺ does not alter the thiophosphorylation pattern of, or the velocity of microtubule translocation by, 14S dynein. The same preincubation conditions that permit or abolish the increase in velocity of microtubule translocation by 22S dynein permit or fail to permit swimming speed of permeabilized cells to increase on reactivation even after cAMP is removed. The effect of cAMP on swimming speed can therefore be accounted for by changes in the mechanically coupled 22S dynein activity via phosphorylation or thiophosphorylation of the 29-kDa polypeptide, which could act as a regulatory dynein light chain.