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

Abstract

The flagellar motor rotates bi-directionally in counter-clockwise (CCW) and clockwise (CW) directions. The motor consists of a stator and a rotor. Recent structural studies have revealed that the stator is composed of a pentameric ring of A subunits and a dimer axis of B subunits. Highly conserved charged and neighboring residues of the A subunit interacts with the rotor, generating torque through a gear-like mechanism. The rotational direction is controlled by chemotaxis signaling transmitted to the rotor, with less evidence for the stator being involved. In this study, we report novel mutations that affect the switching of the rotational direction at the putative interaction site of the stator to generate rotational force. Our results highlight an aspect of flagellar motor function that appropriate switching of the interaction states between the stator and rotor is critical for controlling the rotational direction.

Flagellar motor remodeling during swarming requires FliL

“…This is not surprising in the face of recent results showing that the stators and the rotor function as interlocked gears (Santiveri et al, 2020, Tan et al, 2021. Genetics has also shown that non-functional mutations in rotor proteins are compensated for by suppressors in stator proteins and vice versa (Togashi et al, 1997, Garza et al, 1996, Terashima et al, 2022, Kojima et al, 2011. An important take-home message from this section is that the C ring is not the only player determining rotor bias; the stator complexes, which now include FliL, contribute as well.…”

“…A variety of bacteria alter motor behavior during swarming, increasing motor speed and suppressing tumbles by altering motor bias (Partridge et al, 2019, Tian et al, 2021. We refer to both effects as 'motor remodeling'.…”

Flagellar motor remodeling during swarming requires FliL

“…This is not surprising in the face of recent results showing that the stators and the rotor function as engaged gears (Deme et al, 2020; Santiveri et al, 2020; Tan et al, 2021). Genetics has also shown that nonfunctional mutations in rotor proteins are compensated for by suppressors in stator proteins and vice versa (Garza et al, 1996; Kojima et al, 2011; Terashima et al, 2022; Togashi et al, 1997). An important take‐home message from this section is that the C ring is not the only player determining rotor bias.…”

“…The stator complexes are dynamic, moving in an out of the rotor by sensing how much torque is needed to drive the rotor (Lele et al, 2013; Tipping et al, 2013). When drifting in the membrane, ion flow through the stators is shut off by a “plug” contributed by the MotB subunit of the complex, opening only when the stators dock at the rotor, and when MotA engages with FliG in the C ring (Hosking et al, 2006; Kojima et al, 2009; Terashima et al, 2022). Ion flow through the stators changes the charge of FliG residues at the MotA‐FliG interface, producing torque and rotor movement (Berg & Turner, 1993; Zhou et al, 1998).…”