title: Fission yeast tropomyosin specifies directed transport of myosin-V along actin cables.
abstract: A hallmark of class-V myosins is their processivity--the ability to take multiple steps along actin filaments without dissociating. Our previous work suggested, however, that the fission yeast myosin-V (Myo52p) is a nonprocessive motor whose activity is enhanced by tropomyosin (Cdc8p). Here we investigate the molecular mechanism and physiological relevance of tropomyosin-mediated regulation of Myo52p transport, using a combination of in vitro and in vivo approaches. Single molecules of Myo52p, visualized by total internal reflection fluorescence microscopy, moved processively only when Cdc8p was present on actin filaments. Small ensembles of Myo52p bound to a quantum dot, mimicking the number of motors bound to physiological cargo, also required Cdc8p for continuous motion. Although a truncated form of Myo52p that lacked a cargo-binding domain failed to support function in vivo, it still underwent actin-dependent movement to polarized growth sites. This result suggests that truncated Myo52p lacking cargo, or single molecules of wild-type Myo52p with small cargoes, can undergo processive movement along actin-Cdc8p cables in vivo. Our findings outline a mechanism by which tropomyosin facilitates sorting of transport to specific actin tracks within the cell by switching on myosin processivity.
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Clayton
authors.forename: Luther W
authors.initials: LW
authors.lastname: Pollard
authors.forename: Maria
authors.initials: M
authors.lastname: Sckolnick
authors.forename: Carol S
authors.initials: CS
authors.lastname: Bookwalter
authors.forename: Alex R
authors.initials: AR
authors.lastname: Hodges
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Trybus
authors.forename: Matthew
authors.initials: M
authors.lastname: Lord
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D018797:Cell Cycle Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009218:Myosins / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D012568:Schizosaccharomyces / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D059008:Time-Lapse Imaging
chemical_list: C410737:Cdc8 protein, S pombe; D018797:Cell Cycle Proteins; D029702:Schizosaccharomyces pombe Proteins; D000255:Adenosine Triphosphate; C554097:Myo52 protein, S pombe; D009218:Myosins