title: An accelerated state of myosin-based actin motility.
abstract: We use an in vitro motility assay to determine the biochemical basis for a hypermotile state of myosin-based actin sliding. It is widely assumed that the sole biochemical determinant of actin-sliding velocities, V, is actin-myosin detachment kinetics (1/tauon), yet we recently reported that, above a critical ATP concentration of approximately 100 microM, V exceeds the detachment limit by more than 2-fold. To determine the biochemical basis for this hypermotile state, we measure the effects of ATP and inorganic phosphate, Pi, on V and observe that at low [ATP] V decreases as ln [Pi], whereas above 100 microM ATP the hypermotile V is independent of Pi. The ln [Pi] dependence of V at low [ATP] is consistent with a macroscopic model of muscle shortening, similar to Hill's contractile component, which predicts that V varies linearly with an internal force (Hill's active state) that drives actin movement against the viscous drag of myosin heads strongly bound to actin (Hill's dashpot). At high [ATP], we suggest that the hypermotile V is caused by shear thinning of the resistive population of strongly bound myosin heads. Our data and analysis indicate that, in addition to contributions from tauon and myosin's step size, d, V is influenced by the biochemistry of myosin's working step as well as resistive properties of actin and myosin.
authors.affiliation: Department of Biochemistry, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA.
authors.forename: Anneka M
authors.initials: AM
authors.lastname: Hooft
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Maki
authors.forename: Kristine K
authors.initials: KK
authors.lastname: Cox
authors.forename: Josh E
authors.initials: JE
authors.lastname: Baker
mesh_terms: D000199:Actins / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002465:Cell Movement; D002645:Chickens; D007700:Kinetics; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology; D009218:Myosins / Q000502:physiology*
chemical_list: D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins