Final answer:
The dynactin protein complex facilitates the interaction between cytoplasmic dynein, a cargo vesicle, and a microtubule, assisting in the retrograde transport of vesicles along microtubules in cells.
Step-by-step explanation:
The dynactin protein complex facilitates the interaction between cytoplasmic dynein, a cargo vesicle, and a microtubule. Motor proteins such as dynein, which are ATPases, use the energy from ATP hydrolysis to power intracellular motility, transporting various organelles and vesicles along microtubule tracks inside cells. The dynactin complex, along with cytoplasmic dynein, plays a critical role in this process, particularly in the retrograde movement of vesicles from the nerve endings back to the neuron's cell body. The interaction between dynein and microtubules allows for the transport of organelles, such as secretory vesicles and neurotransmitter vesicles, to different locations within the cell.