Mechanosensitive recruitment of stator units promotes binding of the response regulator CheY-P to the flagellar motor

Abstract

Reversible switching of the bacterial flagellar motor between clockwise (CW) and counterclockwise (CCW) rotation is necessary for chemotaxis, which enables cells to swim towards favorable chemical habitats. Increase in the viscous resistance to the rotation of the motor (mechanical load) inhibits switching. However, cells must maintain homeostasis in switching to navigate within environments of different viscosities. The mechanism by which the cell maintains optimal chemotactic function under varying loads is not understood. Here, we show that the flagellar motor allosterically controls the binding affinity of the chemotaxis response regulator, CheY-P, to the flagellar switch complex by modulating the mechanical forces acting on the rotor. Mechanosensitive CheY-P binding compensates for the load-induced loss of switching by precisely adapting the switch response to a mechanical stimulus. The interplay between mechanical forces and CheY-P binding tunes the chemotactic function to match the load. This adaptive response of the chemotaxis output to mechanical stimuli resembles the proprioceptive feedback in the neuromuscular systems of insects and vertebrates.

Mutations in the stator protein PomA affect switching of rotational direction in bacterial flagellar motor

“…This suggests that the mutation at the position of PomA-L93 or L95 suppresses the shift in the stator position to switch its rotor-interaction side between the inner and outer sides. It has been proposed in a recent report that the increase of force between stator and rotor modulates the binding affinity of the rotor against CheY-P 34 . Based on the proposal, the evidence, that the PomA mutants showed CCW-biased rotation and phenol significantly affected the switching frequency of the flagellar motor, implies that the PomA mutations modulate the force of the stator–rotor interaction, therefore, the binding affinity of the rotor for CheY-P may change.…”

“…The number of stator units incorporating into the motor is dependent on the external mechanical loads 32 , 33 . Increase in the stator incorporation at the viscous load induces conformational shifts in FliM/N, resulting in modulating the binding affinity for CheY-P to the switch complex 34 . An increase in external load increases the binding affinity of the C-ring for CheY-P, suggesting stator–rotor interaction contributes to the switching of rotation direction of the flagellar motor.…”

The Periplasmic Domain of the Ion-Conducting Stator of Bacterial Flagella Regulates Force Generation

“…Such a “catch-bond” mechanism equipped in MotB/PomB leads to an increase in the number of stators that enables the cells to rotate the motor in high viscous load ( Nord et al, 2017 ). New insights were reported recently showing the involvement of the rotor side for mechanosensing in the flagellar motor ( Antani et al, 2021 ).…”

“…One of the notable properties is that the stator has two components: it has a static core, the B subunit, that is necessary to produce stable and constant torque, but it also has a dynamic periphery that allows it to deliver torque. The activity of the stator is regulated in response to environmental stimuli or load changes ( Lele et al, 2013 ; Tipping et al, 2013 ; Antani et al, 2021 ). Here, we review the current state of knowledge about stator structure and function, focusing especially on its assembly-coupled mechanism of activation.…”

The Bacterial Flagellar Motor: Insights Into Torque Generation, Rotational Switching, and Mechanosensing

“…As described above, the C-ring undergoes large structural remodeling upon receiving chemotactic signals from the environment to regulate motor activity, such as switching rotational direction. Mechanosensing by flagellar motors is intimately associated with the change in total ion flux through the stator units ( Lele et al, 2013 ; Belas, 2014 ; Chawla et al, 2017 ; Nord et al, 2017 ; Laganenka et al, 2020 ; Antani et al, 2021 ; Wadhwa et al, 2021 ), which interact with the rotor in a dynamic fashion in response to external load changes ( Figures 2E – G ; Nirody et al, 2016 ; Nord et al, 2017 ; Sato et al, 2019 ; Nakamura et al, 2020 ). The stators units dissociate from the motor more quickly in low-load conditions than in high-load environments ( Wadhwa et al, 2019 ).…”