title: In vitro actin motility velocity varies linearly with the number of myosin impellers.
abstract: Cardiac myosin is the motor powering the heart. It moves actin with 3 step-size varieties generated by torque from the myosin heavy chain lever-arm rotation under the influence of myosin essential light chain whose N-terminal extension binds actin. Proposed mechanisms adapting myosin mechanochemical characteristics on the fly sometimes involve modulation of step-size selection probability via motor strain sensitivity. Strain following the power stroke, hypothetically imposed by the finite actin detachment rate 1/ton, is shown to have no effect on unloaded velocity when multiple myosins are simultaneously strongly actin bound in an in vitro motility assay. Actin filaments slide ∼2 native step-sizes while more than 1 myosin strongly binds actin probably ruling out an actin detachment limited model for imposing strain. It suggests that single myosin estimates for tonare too large, not applicable to the ensemble situation, or both. Parallel motility data quantitation involving instantaneous particle velocities (frame velocity) and actin filament track averaged velocities (track velocity) give an estimate of the random walk step-size, δ. Comparing δ for slow and fast motility components suggests the higher speed component has cardiac myosin upshifting to longer steps. Variable step-size characteristics imply cardiac myosin maintains a velocity dynamic range not involving strain.
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States; Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN 55905, United States. Electronic address: burghardt@mayo.edu.
authors.forename: T P
authors.initials: TP
authors.lastname: Burghardt
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry; D000199:Actins / Q000737:chemistry*; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000327:Adsorption; D000818:Animals; D024722:Cardiac Myosins / Q000737:chemistry*; D002465:Cell Movement; D003432:Cross-Linking Reagents / Q000737:chemistry; D006352:Heart Ventricles / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011336:Probability; D000072417:Protein Domains; D012995:Solubility; D013552:Swine; D013696:Temperature
chemical_list: D000199:Actins; D003432:Cross-Linking Reagents; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D024722:Cardiac Myosins
keywords: Actin detachment limited velocity; Ensemble myosin strain sensing; Independent force generator; Random walk step-size; Velocity histogram probability characteristic