The Architectural Dynamics of the Bacterial Flagellar Motor Switch

Abstract

The rotary bacterial flagellar motor is remarkable in biochemistry for its highly synchronized operation and amplification during switching of rotation sense. The motor is part of the flagellar basal body, a complex multi-protein assembly. Sensory and energy transduction depends on a core of six proteins that are adapted in different species to adjust torque and produce diverse switches. Motor response to chemotactic and environmental stimuli is driven by interactions of the core with small signal proteins. The initial protein interactions are propagated across a multi-subunit cytoplasmic ring to switch torque. Torque reversal triggers structural transitions in the flagellar filament to change motile behavior. Subtle variations in the core components invert or block switch operation. The mechanics of the flagellar switch have been studied with multiple approaches, from protein dynamics to single molecule and cell biophysics. The architecture, driven by recent advances in electron cryo-microscopy, is available for several species. Computational methods have correlated structure with genetic and biochemical databases. The design principles underlying the basis of switch ultra-sensitivity and its dependence on motor torque remain elusive, but tantalizing clues have emerged. This review aims to consolidate recent knowledge into a unified platform that can inspire new research strategies.

Recent Advances in the Bacterial Flagellar Motor Study

“…All review articles provide both expert and non-expert readers with advances in understanding the structures and functions of the bacterial flagellum. They highlight the most recent observations and illustrate perspectives for future research [4][5][6][7][8][9][10][11][12][13].…”

“…The scope of this Special Issue is to cover recent advances in our understanding of the structures and functions of the bacterial flagellar motor derived from different bacterial species. This Special Issue includes ten review articles [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ] and eleven original research papers [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] from well-known experts in the field.…”

Structural basis of the bacterial flagellar motor rotational switching

“…The C ring is made up of the proteins FliG, FliM and FliN and attaches to the cytoplasmic face of the MS ring 2,8,9 . The component FliG contains several subdomains.…”

“…The C-terminal domain of FliG (FliG C ), consisting of the FliG CN and FliG CC subdomains, interacts with the stator and mediates torque generation and transmission 8,9,19 . The middle domain of FliG (FliG M ) binds to FliM that also interacts with FliN 8,9 . The N-terminal domain of FliG (FliG N ) interacts with the C-terminal region of FliF (FliF C ) and connects the C ring to the MS ring 20 .…”

Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure

“…The flagellar T3SS is located at the base of the flagellum and it is one of the earliest structures of the assembly, together with the MS ring of the basal body. The structure and mechanism behind basal body function were a subject of several recent reviews [ 9 , 10 , 11 , 12 ], and they will not be considered further here. Instead, we will focus on the various aspects of the flagellar filament, its components and the role it plays in host–pathogen interactions.…”