Autonomous control mechanism of stator assembly in the bacterial flagellar motor in response to changes in the environment

Abstract

The bacterial flagellar motor is composed of a rotor and a transmembrane ion channel complex that acts as a stator unit. The ion channel complex consists of at least three structural parts: a cytoplasmic domain responsible for the interaction with the rotor, a transmembrane ion channel that forms a pathway for the transit of ions across the cytoplasmic membrane, and a peptidoglycan-binding (PGB) domain that anchors the stator unit to the peptidoglycan (PG) layer. A flexible linker connecting the ion channel and the PGB domain not only coordinates stator assembly with its ion channel activity but also controls the assembly of stator units to the motor in response to changes in the environment. When the ion channel complex encounters the rotor, the N-terminal portion of the PGB domain adopts a partially stretched conformation, allowing the PGB domain to reach and bind to the PG layer. The binding affinity of the PGB domain for the PG layer is affected by the force applied to its anchoring point and to the type of ionic energy source. In this review article, we will present current understanding of autonomous control mechanism of stator assembly in the bacterial flagellar motor.

Mutational analysis of the C‐terminal cytoplasmic domain of FlhB, a transmembrane component of the flagellar type III protein export apparatus in Salmonella

“…The junction connects the hook and filament with distinct mechanical characteristics. The filament cap promotes the assembly of FliC into the long helical filament (Macnab, ; Minamino & Imada, ; Minamino, Terahara, Kojima, & Namba, ).…”

Structural and functional characterisation of SiiA, an auxiliary protein from the SPI4-encoded type 1 secretion system fromSalmonella enterica

“…2ZVY [19]). The binding behavior of the latter has been extensively studied before (for a recent review see [21]).…”

“…In the 309 residue-long MotB from S. Typhimurium this architecture consists of a transmembrane helix (aa 29-50), a plug helix (aa [53][54][55][56][57][58][59][60][61][62][63][64][65][66], and a C-terminal segment named 'periplasmic region essential for mobility' (PEM, aa 111-270) that also contains an OmpAlike PG-binding domain (aa 149-269) [18][19][20][21]. The PG-binding domain enables interaction with the PG layer in Gram-negative bacteria.…”

Direct observation of speed fluctuations of flagellar motor rotation at extremely low load close to zero

“…The association and dissociation cycle of MotA with FliG is coupled with inward‐directed proton translocation through the transmembrane proton channel of the MotAB complex. Motor torque is believed to be generated by the following scheme: (a) proton from the cell exterior binds to a highly conserved Asp residue of MotB within the transmembrane proton channel (Asp‐32 in E. coli MotB and Asp‐33 in Salmonella MotB); (b) this proton‐binding induces a conformational change of the MotAB stator complex, allowing MotA to interact with FliG on the rotor, forcing the rotor to move forward; (c) proton is released from the proton channel to the cytoplasm and the MotAB stator complex dissociates from the rotor; (d) the stator conformation recovers to the free form (Minamino, Terahara, Kojima, & Namba, ).…”