title: Myosin-IXb is a single-headed and processive motor.
abstract: Class IX myosins are unique among the many classes of known actin-based motors in that the tail region of these myosins contains a GTPase-activating protein domain for the small GTP-binding protein, Rho. Previous studies on human myosin-IXb indicate that this myosin is mechanochemically active and exhibits actin-binding properties similar to the processive motor, myosin-Va. Motility analysis of antibody-tethered myosin-IXb performed using the sliding actin filament assay indicates that this myosin does exhibit properties characteristic of a processive motor. Like myosin-Va, the velocity of myosin-IXb remains constant (38.2 +/- 1.2 nm/s) even at single motor/filament densities. At low motor densities, filaments can be seen passing through and pivoting about single points on the motility surface. Analysis of filament landing rates as a function of motor density also indicates that a single motor is sufficient for filament movement. However, in contrast to myosin-Va, which uses coordinated motion of its two heads to move processively along the filament, hydrodynamic and chemical cross-linking studies indicate that under the conditions tested, myosin-IXb is a single-headed motor consisting of a single heavy chain and associated light chains.
authors.affiliation: Department of Molecular, Yale University, New Haven, Connecticut 06520-8103, USA.
authors.forename: Penny L
authors.initials: PL
authors.lastname: Post
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Tyska
authors.forename: Christopher B
authors.initials: CB
authors.lastname: O'Connell
authors.forename: Kimberly
authors.initials: K
authors.lastname: Johung
authors.forename: Amanda
authors.initials: A
authors.lastname: Hayward
authors.forename: Mark S
authors.initials: MS
authors.lastname: Mooseker
mesh_terms: D002465:Cell Movement; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D020558:GTP Phosphohydrolases / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D007962:Leukocytes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000378:metabolism; D024701:Myosin Type V / Q000737:chemistry / Q000378:metabolism; D009218:Myosins / Q000737:chemistry* / Q000502:physiology*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: D003432:Cross-Linking Reagents; C113469:myosin IXB; C077511:MYO5A protein, human; D020558:GTP Phosphohydrolases; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D009218:Myosins