The Role of Entropy and Enthalpy of Actin Filaments in Cellular Actin-Based Processes: Two Examples

Abstract

Actin filaments play a fundamental role in cell migration and cell mechanics. Assembled by different Actin-Binding Proteins into different structures -cortex, stress fibers, filipodia, lamellipodium- actin filament is the basic unit available for the cell to apply forces or carry tensions. Actin filament is a semi-flexible polymer at the scale of the cell, which means that it is able to bend and to be bent by thermal fluctuations but it is mostly straight. This leads to a large contribution of the entropy to the dynamics of actin filaments and the networks they form. Here will be discussed our recent results regarding the link between these individual actin filament properties, semi-flexible fluctuating filaments, and their role in two examples: the actin-based force generation and the mechanics of the lamellipodium. We have recently shown that the polymerization of actin filaments that experience orientational fluctuations generates forces in a mechanism associated to the reduction of their entropy (1). In another experiments we have investigated the link between the elastic response of dense Arp2/3 branched actin networks and their microscopic architecture -in terms of branching and capping concentrations. Our results indicate that the elasticity of such dense branched networks originates more in the “enthalpic” deformations of the filaments themselves than in the “entropic” response usually probed in more diluted actin gels (2).(1) Brangbour et al (2011) Force-Velocity Measurements of a Few Growing Actin Filaments. PLoS Biology 9 e1000613.(2) Pujol et (2012) Impact of branching on the elasticity of actin networks. PNAS 109, p10364-9.