Motor transport of self-assembled cargos in crowded environments.

Intracellular transport of cargo particles is performed by multiple motors working in concert. However, the mechanism of motor association to cargos is unknown. It is also unknown how long individual motors stay attached, how many are active, and how multimotor cargos would navigate a densely crowded filament with many other motors. Prior theoretical and experimental biophysical model systems of intracellular cargo have assumed fixed teams of motors transporting along bare microtubules or microtubules with fixed obstacles. Here, we investigate a regime of cargos transporting along microtubules crowded with free motors. Furthermore, we use cargos that are able to associate or dissociate motors as it translocates. We perform in vitro motility reconstitution experiments with high-resolution particle tracking. Our model system consists of a quantum dot cargo attached to kinesin motors, and additional free kinesin motors that act as traffic along the microtubule. Although high densities of kinesin motors hinder forward motion, resulting in a lower velocity, the ability to associate motors appears to enhance the run length and attachment time of the quantum dot, improving overall cargo transport. These results suggest that cargos that can associate new motors as they transport could overcome traffic jams.