Bistability in filamentous actin through monomer-sequestration of an effector species

TL;DR

This paper models filamentous actin dynamics, demonstrating that a single effector species can induce bistability in actin filament populations, with potential for switching states via transient G-actin pool manipulation.

Contribution

It introduces a novel class of models showing bistability in actin dynamics driven by monomer-sequestration of effectors, supported by analytical solutions and stochastic simulations.

Findings

Bistability predicted in all proposed models.

Switching between states achievable by transient G-actin manipulation.

Analytical solutions confirm model predictions.

Abstract

Filamentous actin, a species of dynamic protein polymers, is one of the main components of the cytoskeleton of eukaryotic cells. We formulate a class of models that predict the possibility of bistable steady states in populations of dynamic actin filaments. They are built upon a basic model of actin dynamics that includes severing and capping in the presence of a finite actin monomer pool. The key additional ingredient is the presence of a single species of effector molecules that is partially sequestered to an inactive state by binding to free G-actin. In its unbound active state, this effector species can \emph{enhance} the rate of nucleation of filamentous actin or its growth speed, or \emph{inhibit} the activity of capping or severing proteins. Using an explicit analytical solution of the basic actin dynamics model, we show that bistability is predicted to occur in all of the proposed models. We verify these predictions using particle-based stochastic simulations. In addition, we show that switching between the two stable states can be achieved by transient manipulation of the free G-actin pool size.