Dr. George Shubeita, University of Texas
The cytosol is crowded by a high concentration of macromolecules. Crowding can alter protein conformation, binding rates, and reaction kinetics, yet it is not known how crowding affects cargo transport by molecular motors. I will report on experiments in which we mimicked cellular crowding in vitro to study its consequences on cargo transport by kinesin -1 motors.
Surprisingly, we find that crowding significantly slows transport by teams of motors, while having a negligible effect on single motor run-length or velocity. To understand how this multiple-molecule behavior emerges from single motor properties, we applied controlled forces on single motors and motor ensembles using an optical trap. We find that the detachment kinetics of individual motors in response to force depend on the presence of crowding agents. This change in motor response not only explains the differences in the velocity of multiple-motor transport that we observe, but also makes predictions on how cargoes transported by motor ensembles should respond to force, which we confirm using the optical trap.
Finally, since in vivo transport is accomplished by multiple-motors and in crowded conditions, our studies suggest that both aspects are necessary to understand kinesin function in the cell. Indeed, we find that transport by ensembles of motors in living cells is impacted by crowding similarly to what we observe in vitro.