Abstract
The bacterial flagellum is a complex and dynamic nanomachine that propels bacteria through liquids. It consists of a basal body, a hook, and a long filament. The flagellar filament is composed of thousands of copies of the protein flagellin (FliC) arranged helically and ending with a filament cap composed of an oligomer of the protein FliD. The overall structure of the filament core is preserved across bacterial species, while the outer domains exhibit high variability, and in some cases are even completely absent. Flagellar assembly is a complex and energetically costly process triggered by environmental stimuli and, accordingly, highly regulated on transcriptional, translational and post-translational levels. Apart from its role in locomotion, the filament is critically important in several other aspects of bacterial survival, reproduction and pathogenicity, such as adhesion to surfaces, secretion of virulence factors and formation of biofilms. Additionally, due to its ability to provoke potent immune responses, flagellins have a role as adjuvants in vaccine development. In this review, we summarize the latest knowledge on the structure of flagellins, capping proteins and filaments, as well as their regulation and role during the colonization and infection of the host.
Highlights
The bacterial flagellum is one of the most complex and dynamic biological nanomachines known and has attracted attention since its discovery in the late nineteenth century.The history of flagellar research is an excellent example of the gradual transition of biological studies, that were purely morphological, to biochemical and biophysical studies at the atomic level, allowing current understanding to the point of being able to modify it for various purposes.Bacterial flagella are appendages on the cell body that provide motility
The export of flagellar proteins is a highly organized and well-controlled process conducted by the flagellar type 3 secretion system (T3SS) apparatus located at the base of the flagellum, and powered by ATP and proton motive force (PMF) across the cytoplasmic membrane as the energy sources [99,136,146,147,148]
On the other hand, when it comes to the direct role of flagellin and FliD in adhesion in C. difficile and H. pylori, reports are somewhat contradictory in the literature, with some studies showing their direct involvement in different cell types [172,173], while others suggest that their importance is limited to providing motility while other adhesins mediate binding to colonize the gastric epithelial cells [159,174]
Summary
The bacterial flagellum is one of the most complex and dynamic biological nanomachines known and has attracted attention since its discovery in the late nineteenth century. The basal body is a complex assembly that functions as a motor powered by a proton gradient; its rotation generates torque This torque is transmitted through the hook to the filament that serves as a propeller, creating thrust and pushing bacteria through liquid environments [3]. Filaments are much longer than the cell body and during smooth swimming they adopt a left-handed supercoiled corkscrew shape, while clockwise rotation changes the handedness [5,6] In species such as Vibrio cholerae and H. pylori, flagella are enclosed by a sheath—a membranous structure contiguous with the outer membrane with various proposed functions, such as the prevention of filament disintegration in gastric acid, immune evasion and the place of origin of the outer-membrane vesicles that protect bacteria from bacteriophages [7]. We will focus on the various aspects of the flagellar filament, its components and the role it plays in host–pathogen interactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
