Steady-state MreB helices inside bacteria: dynamics without motors

TL;DR

This paper models the dynamics of MreB helices in bacteria, revealing how their structure and turnover can occur without motor proteins, through force-dependent polymerization and elastic buckling.

Contribution

It introduces a combined force-dependent polymerization and elastic buckling model for MreB helices, explaining their formation, dynamics, and polar localization without motor proteins.

Findings

Stochastic fluctuations significantly affect MreB helix dynamics.

Helical pitch evolves with cell growth and exhibits specific turnover times.

Protofilament tips move in opposite directions, enabling targeted localization.

Abstract

Within individual bacteria, we combine force-dependent polymerization dynamics of individual MreB protofilaments with an elastic model of protofilament bundles buckled into helical configurations. We use variational techniques and stochastic simulations to relate the pitch of the MreB helix, the total abundance of MreB, and the number of protofilaments. By comparing our simulations with mean-field calculations, we find that stochastic fluctuations are significant. We examine the quasi-static evolution of the helical pitch with cell growth, as well as timescales of helix turnover and denovo establishment. We find that while the body of a polarized MreB helix treadmills towards its slow-growing end, the fast-growing tips of laterally associated protofilaments move towards the opposite fast-growing end of the MreB helix. This offers a possible mechanism for targeted polar localization without cytoplasmic motor proteins.