title: Kinesin-73 is a processive motor that localizes to Rab5-containing organelles.
abstract: Drosophila Kinesin-73 (Khc-73), which plays a role in mitotic spindle polarity in neuroblasts, is a metazoan-specific member of the Kinesin-3 family of motors, which includes mammalian KIF1A and Caenorhabditis elegans Unc-104. The mechanism of Kinesin-3 motors has been controversial because some studies have reported that they transport cargo as monomers whereas other studies have suggested a dimer mechanism. Here, we have performed single-molecule motility and cell biological studies of Khc-73. We find that constructs containing the motor and the conserved short stretches of putative coiled-coil-forming regions are predominantly monomeric in vitro, but that dimerization allows for fast, processive movement and high force production (7 piconewtons). In Drosophila cell lines, we present evidence that Khc-73 can dimerize in vivo. We also show that Khc-73 is recruited specifically to Rab5-containing endosomes through its "tail" domain. Our results suggest that the N-terminal half of Khc-73 can undergo a monomer-dimer transition to produce a fast processive motor and that its C-terminal half possesses a specific Rab5-vesicle binding domain.
authors.affiliation: Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158-2517, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Huckaba
authors.forename: Arne
authors.initials: A
authors.lastname: Gennerich
authors.forename: James E
authors.initials: JE
authors.lastname: Wilhelm
authors.forename: Athar H
authors.initials: AH
authors.lastname: Chishti
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Vale
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001703:Biophysics; D002460:Cell Line; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D019281:Dimerization; D004330:Drosophila / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D016547:Kinesins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; C104644:Khc-73 protein, Drosophila; D020409:Molecular Motor Proteins; D016547:Kinesins; D020696:rab5 GTP-Binding Proteins