title: Control of the initiation and termination of kinesin-1-driven transport by myosin-Ic and nonmuscle tropomyosin.
abstract: Intracellular transport is largely driven by processive microtubule- and actin-based molecular motors. Nonprocessive motors have also been localized to trafficking cargos, but their roles are not well understood. Myosin-Ic (Myo1c), a nonprocessive actin motor, functions in a variety of exocytic events, although the underlying mechanisms are not yet clear. To investigate the interplay between myosin-I and the canonical long-distance transport motor kinesin-1, we attached both motor types to lipid membrane-coated bead cargo, using an attachment strategy that allows motors to actively reorganize within the membrane in response to the local cytoskeletal environment. We compared the motility of kinesin-1-driven cargos in the absence and presence of Myo1c at engineered actin/microtubule intersections. We found that Myo1c significantly increases the frequency of kinesin-1-driven microtubule-based runs that begin at actin/microtubule intersections. Myo1c also regulates the termination of processive runs. Beads with both motors bound have a significantly higher probability of pausing at actin/microtubule intersections, remaining tethered for an average of 20 s, with some pauses lasting longer than 200 s. The actin-binding protein nonmuscle tropomyosin (Tm) provides spatially specific regulation of interactions between myosin motors and actin filaments in vivo; in the crossed-filament in vitro assay, we found that Tm2-actin abolishes Myo1c-specific effects on both run initiation and run termination. Together, these observations suggest Myo1c is important for the selective initiation and termination of kinesin-1-driven runs along microtubules at specific actin filament populations within the cell.
authors: The Pennsylvania Muscle Institute and Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6085, USA.
authors: Betsy B
authors: BB
authors: McIntosh
authors: The Pennsylvania Muscle Institute and Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6085, USA. Electronic address: holzbaur@mail.med.upenn.edu.
authors: Erika L F
authors: EL
authors: Holzbaur
authors: The Pennsylvania Muscle Institute and Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6085, USA. Electronic address: ostap@mail.med.upenn.edu.
authors: E Michael
authors: EM
authors: Ostap
mesh_terms: D002465:Cell Movement; D003599:Cytoskeleton / Q000378:metabolism*; D006801:Humans; D016547:Kinesins / Q000235:genetics* / Q000378:metabolism; D024461:Myosin Type I / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D014335:Tropomyosin / Q000235:genetics* / Q000378:metabolism
chemical_list: C488101:KIF5B protein, human; C518659:TPM2 protein, human; D014335:Tropomyosin; D024461:Myosin Type I; C460367:MYO1C protein, human; D016547:Kinesins