Fluctuation of actin sliding over myosin thick filaments <i>in vitro</i>

Abstract

It is customarily thought that myosin motors act as independent force-generators in both isotonic unloaded shortening as well as isometric contraction of muscle. We tested this assumption regarding unloaded shortening, by analyzing the fluctuation of the actin sliding movement over long native thick filaments from molluscan smooth muscle in vitro. This analysis is based on the prediction that the effective diffusion coefficient of actin, a measure of the fluctuation, is proportional to the inverse of the number of myosin motors generating the sliding movement of an actin filament, hence proportional to the inverse of the actin length, when the actions of the motors are stochastic and statistically independent. Contrary to this prediction, we found the effective diffusion coefficient to be virtually independent of, and thus not proportional to, the inverse of the actin length. This result shows that the myosin motors are not independent force-generators when generating the continuous sliding movement of actin in vitro and that the sliding motion is a macroscopic manifestation of the cooperative actions of the microscopic ensemble motors.

Comparing Guiding Track Requirements for Myosin- and Kinesin-Powered Molecular Shuttles

“…Our value of v avg = 2.8 μm/s reproduced our previous results . The obtained value of D v-flu = 5.0 × 10 −2 μm 2 /s is comparable with those reported by Noda et al of 3.7 × 10 −2 and 1.5 × 10 −2 μm 2 /s for AFs gliding along native thick filaments from M. galloprovincialis and S. virgatus , respectively …”

“…21 The obtained value of D v-flu ) 5.0 × 10 -2 µm 2 /s is comparable with those reported by Noda et al of 3.7 × 10 -2 and 1.5 × 10 -2 µm 2 /s for AFs gliding along native thick filaments from M. galloproVincialis and S. Virgatus, respectively. 20 To validate our analysis procedure further, 22 a computer simulation of AF gliding on a myosin-coated planar surface was carried out with V avg ) 2.8 µm/s, D v-flu ) 5.0 × 10 -2 µm 2 /s, L p ) 8.8 µm, and a time step of ∆t ) 0.01 s for a simulated duration of 500 s, which results in a trajectory length comparable to the total trajectory length of all 28 trajectories analyzed. The simulated trajectory was analyzed in the same manner as the experiment, and the parameters were retrieved to be V avg ) 2.8 µm/s (SD ) 0.02 µm/s), D v-flu ) 5.1 ( 0.5 × 10 -2 µm 2 /s, and L p ) 9.3 ( 1.7 µm (mean ( SD; N ) 10).…”

“…The trajectory analysis yielded two previously known parameters, 20 the average velocity, V avg , and the motional diffusion coefficient, D v-flu , as well as two previously unknown parameters, the trajectory persistence length, L p , and the variance of average filament velocities, 〈(∆V avg ) 2 〉.…”

Models of protein linear molecular motors for dynamic nanodevices

“…With this formalism in mind, the motion is characterised by calculating for the leading tip: 190,191 (i) the average velocity; (ii) the tangent angle, which gives the orientation of the trajectory; (iii) the variance of the tangent angle expressed in terms of the effective diffusion coefficient; (iv) the trajectory persistence length.…”

Anomalous Fluctuations in Sliding Motion of Cytoskeletal Filaments Driven by Molecular Motors: Model Simulations

“…Recently, Imafuku and co-workers have done a series of experiments on filament motion driven by many molecular motors. Focusing on the fluctuation rather than the average motion, they have revealed an intriguing aspect of cooperativity in the collective action. − …”