Cooperative stator assembly of bacterial flagellar motor mediated by rotation

Kenta I Ito,Shoichi Toyabe,Shuichi Nakamura

doi:10.1038/s41467-021-23516-y

Abstract

Cooperativity has a central place in biological regulation, providing robust and highly-sensitive regulation. The bacterial flagellar motor implements autonomous torque regulation based on the stator’s dynamic structure; the stator units bind to and dissociate from the motor dynamically in response to environmental changes. However, the mechanism of this dynamic assembly is not fully understood. Here, we demonstrate the cooperativity in the stator assembly dynamics. The binding is slow at the stalled state, but externally forced rotation as well as driving by motor torque in either direction boosts the stator binding. Hence, once a stator unit binds, it drives the rotor and triggers the avalanche of succeeding bindings. This cooperative mechanism based on nonequilibrium allostery accords with the recently-proposed gear-type coupling between the rotor and stator.

Highlights

Cooperativity has a central place in biological regulation, providing robust and highlysensitive regulation
Swimming bacteria like Escherichia coli and Salmonella enterica have been serving as the model system of motility regulation
The bacterial flagellar motor (BFM)[1,2,3,4] (Fig. 1a) is a large protein complex and can rotate at up to 1700 Hz5, reverse the rotation, and vary the torque depending on the load on the motor

Summary

Introduction

Cooperativity has a central place in biological regulation, providing robust and highlysensitive regulation. The binding is slow at the stalled state, but externally forced rotation as well as driving by motor torque in either direction boosts the stator binding. A striking fact is that the BFM has multiple torque-generating stator units and regulates the torque magnitude by dynamically alternating the units between the motor and surrounding membrane pool[6,7,8] (Fig. 1b). This autonomous stator assembly relies on the self-regulation of each stator unit. Since the binding of the first stator unit causes the rotation, there is a cooperative feedback loop of the stator assembly via rotation

Methods

Results

Conclusion