title: Myosin IXb is a single-headed minus-end-directed processive motor.
abstract: Myosin is an actin-based molecular motor that constitutes a diverse superfamily. In contrast to conventional myosin, which binds to actin for only a short time during cross-bridge cycling, recent studies have demonstrated that class V myosin moves along actin filaments for a long distance without dissociating. This would make it suitable for supporting cargo movement in cells. Because myosin V has a two-headed structure with an expanded neck domain, it has been postulated to 'walk' along the 36-nm helical repeat of the actin filament, with one head attached to the actin and leading the other head to the neighbouring helical pitch. Here, we report that myosin IXb, a single-headed myosin, moves processively on actin filaments. Furthermore, we found that myosin IXb is a minus-end-directed motor. In addition to class VI myosin, this is the first myosin superfamily member identified that moves in the reverse direction. The processive movement of the single-headed myosin IXb cannot be explained by a 'hand-over-hand' mechanism. This suggests that an alternative mechanism must be operating for the processive movement of single-headed myosin IXb.
authors.affiliation: Department of Physiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655-0127, USA.
authors.forename: Akira
authors.initials: A
authors.lastname: Inoue
authors.forename: Junya
authors.initials: J
authors.lastname: Saito
authors.forename: Reiko
authors.initials: R
authors.lastname: Ikebe
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Ikebe
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005822:Genetic Vectors; D007313:Insecta; D008856:Microscopy, Fluorescence; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D000199:Actins; D018076:DNA, Complementary; D011994:Recombinant Proteins; C113469:myosin IXB; D009218:Myosins