Abstract
We report a coarse-grained molecular dynamics simulation study of a bundle of parallel actin filaments under supercritical conditions pressing against a loaded mobile wall using a particle-based approach where each particle represents an actin unit. The filaments are grafted to a fixed wall at one end and are reactive at the other end, where they can perform single monomer (de)polymerization steps and push on a mobile obstacle. We simulate a reactive grand canonical ensemble in a box of fixed transverse area A, with a fixed number of grafted filaments , at temperature T and monomer chemical potential . For a single filament case () and for a bundle of filaments, we analyze the structural and dynamical properties at equilibrium where the external load compensates the average force exerted by the bundle. The dynamics of the bundle-moving-wall unit are characteristic of an over-damped Brownian oscillator in agreement with recent in vitro experiments by an optical trap setup. We analyze the influence of the pressing wall on the kinetic rates of (de)polymerization events for the filaments. Both static and dynamic results compare reasonably well with recent theoretical treatments of the same system. Thus, we consider the proposed model as a good tool to investigate the properties of a bundle of living filaments.
Highlights
When a bundle of parallel actin filaments in supercritical conditions hits a moving wall subject to an opposing constant load force FL, the balance between the polymerization force, the load and the friction force from the solvent leads to a stationary velocity v of the obstacle.Here, v indicates a coarse-grained velocity averaged over rapid fluctuations due to microscopic events, like the addition/removal of single monomers occurring at the bundle tip and to the usual wall Brownian motion
We have presented a particle-based model to simulate the dynamics of a grafted bundle of parallel living actin filaments pushing on a mobile wall subject to load
Our goal is to provide a working model to study, e.g., the growth of F-actin filopodia against a resisting membrane
Summary
When a bundle of parallel actin filaments in supercritical conditions hits a moving wall subject to an opposing constant load force FL , the balance between the polymerization force, the load and the friction force from the solvent (usually negligible) leads to a stationary velocity v of the obstacle. V indicates a coarse-grained velocity averaged over rapid fluctuations due to microscopic events, like the addition/removal of single monomers occurring at the bundle tip and to the usual wall Brownian motion. A stationary non-equilibrium state is only possible if the living filaments are rigid so that the distribution of the tip-wall distance(s) (for single or many filaments) becomes independent on the length of the bundle [1,2,3,4] and independent of time in a time window. Any polymerization attempt e 0 ) is rejected if it leads to overlap with the wall, but is accepted otherwise
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