The effect of active fluctuations on the dynamics of particles, motors and hairpins

TL;DR

This paper introduces a modified Langevin model to study how active fluctuations from molecular motors influence particle and polymer dynamics, revealing superdiffusive to subdiffusive transitions and barrier lowering effects.

Contribution

It presents a novel Langevin framework incorporating active fluctuations, explaining experimental observations and modeling biological processes like kinesin movement and DNA hairpin dynamics.

Findings

Particle motion transitions from superdiffusive to subdiffusive.

Active forces double the probability of a particle near its binding site.

Active fluctuations lower the energy barrier for DNA hairpin zipping/unzipping.

Abstract

Inspired by recent experiments on the dynamics of particles and polymers in artificial cytoskeletons and in cells, we introduce a modified Langevin equation for a particle in an environment that is a viscoelastic medium and that is brought out of equilibrium by the action of active fluctuations caused by molecular motors. We show that within such a model, the motion of a free particle crosses over from superdiffusive to subdiffusive as observed for tracer particles in an {\it in vitro} cytoskeleton or in a cell. We investigate the dynamics of a particle confined by a harmonic potential as a simple model for the motion of the tethered head of kinesin-1. We find that the probability that the head is close to its binding site on the microtubule can be enhanced by a factor of two due to active forces. Finally, we study the dynamics of a particle in a double well potential as a model for the dynamics of DNA-hairpins. We show that the active forces effectively lower the potential barrier between the two minima and study the impact of this phenomenon on the zipping/unzipping rate.