Chemotaxis signaling protein CheY binds to the rotor protein FliN to control the direction of flagellar rotation in Escherichia coli

Abstract

The direction of rotation of the Escherichia coli flagellum is controlled by an assembly called the switch complex formed from multiple subunits of the proteins FliG, FliM, and FliN. Structurally, the switch complex corresponds to a drum-shaped feature at the bottom of the basal body, termed the C-ring. Stimulus-regulated reversals in flagellar motor rotation are the basis for directed movement such as chemotaxis. In E. coli, the motors turn counterclockwise (CCW) in their default state, allowing the several filaments on a cell to join together in a bundle and propel the cell smoothly forward. In response to the chemotaxis signaling molecule phospho-CheY (CheY P ), the motors can switch to clockwise (CW) rotation, causing dissociation of the filament bundle and reorientation of the cell. CheY P has previously been shown to bind to a conserved segment near the N terminus of FliM. Here, we show that this interaction serves to capture CheY P and that the switch to CW rotation involves the subsequent interaction of CheY P with FliN. FliN is located at the bottom of the C-ring, in close association with the C-terminal domain of FliM (FliM C ), and the switch to CW rotation has been shown to involve relative movement of FliN and FliM C . Using a recently developed structural model for the FliN/FliM C array, and the CheY P -binding site here identified on FliN, we propose a mechanism by which CheY P binding could induce the conformational switch to CW rotation.switching | cell motility | signal transduction | molecular motors M any motile bacteria control the direction of their swimming by regulating the sense of flagellar rotation in response to sensory cues. In the well-studied enteric species Escherichia coli and Salmonella (Salmonella enterica serovar typhimurium), counterclockwise (CCW) rotation allows the several flagellar filaments on a cell to join in a bundle to propel the cell smoothly, whereas clockwise (CW) rotation of one or more flagella disrupts the bundle and causes the cell to tumble. In the absence of external stimuli, a cell executes smooth runs of about a second punctuated by brief tumbles that send it in a new, essentially random, direction; by delaying the switch to CW rotation in response to attractant stimuli, cells prolong runs that happen to be in a favorable direction and so bias their movement toward nutrients, temperatures, or other factors conducive to survival (1, 2).

Mechanism for adaptive remodeling of the bacterial flagellar switch

“…An independent two-sample t test indicated that this difference was significant (P < 0.001). We did not observe significant correlation between FliM numbers and rotational velocities over a range of speeds typical for tethered cells (1)(2)(3)(4)(5)(6)(7)(8).Because the results of the cryo-EM studies might have been biased, we consider the ratio of the average number of FliM subunits in a given motor to that observed for motors in the CW …”

Evidence for symmetry in the elementary process of bidirectional torque generation by the bacterial flagellar motor

“…The switching probability is modified by a chemotactic signal transduction pathway (1,6). The binding of a chemotactic signalling protein, phospho-CheY (CheY-P), to FliM and FliN is thought to induce a cooperative conformational change in the C-terminal FliG domains of the C ring, resulting in a different rotor-stator interaction to allow the motor to spin in the CW direction (16,17). The switching probability increases linearly with increase in motor torque in both directions, suggesting that the switch senses the load on the stator-rotor interaction as well as the level of CheY-P (18).…”

Chemotaxis inCampylobacter Jejuni

“…Non-phosphorylated CheY interacts weakly with the FliM switch proteins of the flagellar motor, which are the final effectors of the sensory transduction chain [42][43][44][45]. Because of the only weak interaction between unphosphorylated CheY and FliM, CheY is not able to break up the FliNFliN interaction within the FliN-dimer via the N-terminal hydrophobic patch [46]. Thus, a CheY-FliN interaction does not take place and a counterclockwise rotation of the flagella is induced leading to a fast straightforward movement of the bacterial cell, a so-called "run".…”

“…CheY-P interacts as well with the N-terminal parts of the FliM proteins of the motor switch complex but in a stronger way than non-phosphorylated CheY [43]. This stronger binding tethers CheY-P to FliM so that it is able to break up FliN-dimers to bind to FliN [46]. Thus, it triggers a clockwise flagellar rotation resulting in bacterial "tumbling" [44,46].…”

“…This stronger binding tethers CheY-P to FliM so that it is able to break up FliN-dimers to bind to FliN [46]. Thus, it triggers a clockwise flagellar rotation resulting in bacterial "tumbling" [44,46].…”