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Phosphorylation regulates auto-inhibition of kinesin KIF3A

Kinesin are molecular motors that move along the microtubules. They function to transport cargoes, vesicles and organelles to designated locations in the cells. KIF3A belongs to the Kinesin-2 family and forms a heterotrimeric complex with KIF3B and KAP3. We have earlier shown that the cargo trafficking activity of KIF3 motor can be regulated by CaMKII kinase and POPX2 phosphatase. In this study, we elucidated the mechanism of KIF3A regulation. We find that KIF3A adopts an auto-inhibited state through the interaction between the motor and tail domains. The motor-tail interaction also hinders the ATPase activity of the motor domain. We show that the phosphorylation status of serine-689/690 (mouse/human) at the C-terminal region of KIF3A is crucial for the motor-tail interaction. The motor domain does not interact well with the tail domain when serine-689 is phosphorylated by CaMKII or mutated to aspartic acid to mimic phosphorylation. Molecular dynamics simulations suggest that the non-phosphorylated tail domain folds into the hydrophobic pocket formed by the motor dimers. Phosphorylation of serine-689 results in conformational changes that leads to the relieve of auto-inhibition.