What is the role of Myosin V in intracellular transport?
Myosin V is prototypical class V unconventional myosin that operates on actin filaments not microtubules serving local delivery after long range microtubule transport. The molecule is dimeric with two motor heads each containing six calmodulin or essential light chain IQ motifs forming a 24 nm lever arm, a coiled coil stalk and a globular tail domain that binds cargo adaptors such as Rab11, Rab27, melanophilin and Myo4p binding proteins. It moves processively hand over hand toward barbed plus end near plasma membrane hydrolyzing one ATP per step with coordinated gating that prevents simultaneous detachment. The motor center of mass advances 36 nm per ATP matching actin helical repeat of 13 monomers while each head swings about 72 nm. This architecture allows organelles, secretory vesicles, endoplasmic reticulum tubules, mRNA granules and melanosomes to traverse dense cortical actin networks where kinesin and dynein cannot operate. Regulation involves cargo binding relieving autoinhibition, calcium calmodulin influencing lever stiffness and coincidence detection with Rab GTPases ensuring correct delivery and recycling.
Ref: Vale, Cell 2003; Hammer & Sellers, Nat Rev Mol Cell Biol 2012 – Myosin V processive transport on actin filaments.