Coordination of Multiple Motors Bound to Intracellular Cargos

Abstract

The movement of organelles and vesicles along the cellular cytoskeleton is often driven by multiple motor types, including kinesins, dynein, and myosins. Both in vitro and cellular studies suggest that multiple motors are bound simultaneously to intracellular cargos. For some cargos, such as late endosomes/lysosomes, we find that opposing motors may be active simultaneously, leading to stochastic directional switching best characterized as a tug-of-war. Run lengths are generally short and apparent diffusive movement predominates. For other cargos, such as autophagosomes, both kinesin and dynein motors remain stably bound but motility is highly processive in a single direction, suggesting motor activities are regulated. Intracellular transport is also regulated at the level of the track, as dictated by the complex organization of the intracellular cytoskeleton, characterized by microtubule-microtubule and microtubule-actin filament intersections as well as filament dynamics and filament-binding proteins. By analyzing motility at multiple levels, including: (1) in vitro with purified motors bound to beads at filament intersections; (2) in vitro with motors that co-purify with isolated organelles; (3) in the cell using high resolution tracking of endocytosed quantum dots; and (4) intracellular manipulation of phagocytosed beads using an optical trap, we can investigate the mechanisms that coordinate the interactions of multiple motors in intracellular organelle transport. Supported by NIH GM087253.