bacterial-type flagellum assembly

Definition

Target type: biologicalprocess

The assembly of a bacterial-type flagellum, a motor complex composed of an extracellular helical protein filament coupled to a rotary motor embedded in the cell envelope which functions in cell motility. [GOC:jl]

Bacterial flagella are complex, helical protein filaments that extend from the cell surface and facilitate bacterial motility. Their assembly is a highly regulated process involving multiple proteins and steps.

**1. Basal Body Formation:**
The flagellum begins its assembly at the base, where a basal body structure is formed. This structure consists of a series of rings embedded in the cell envelope, providing an anchor for the flagellum. The basal body acts as a molecular motor, generating the force required for rotation.

**2. Hook Assembly:**
A short, curved structure called the hook connects the basal body to the filament. The hook acts as a flexible joint, allowing the filament to rotate independently of the basal body.

**3. Filament Polymerization:**
The filament, the long, helical structure that propels the bacterium, is composed of multiple copies of the protein flagellin. Flagellin subunits assemble into a hollow cylinder, forming the filament. This assembly process occurs at the distal end of the growing filament.

**4. Flagellin Export and Assembly:**
Flagellin is synthesized in the cytoplasm and transported to the cell surface through a dedicated export pathway. This pathway involves a specialized protein complex called the flagellar type III secretion system (T3SS). The T3SS acts as a molecular syringe, injecting flagellin subunits directly into the growing filament.

**5. Cap Protein:**
At the tip of the growing filament, a specialized protein called the cap protein plays a critical role in filament assembly. The cap protein binds to the growing filament and acts as a template, directing the assembly of flagellin subunits.

**6. Regulation and Control:**
Flagellar assembly is tightly regulated by a complex network of genes and proteins. These regulatory mechanisms ensure that the flagellum is assembled at the appropriate time and location, and that the process is coordinated with other cellular processes.

**7. Flagellum Rotation:**
Once assembled, the flagellum rotates, propelling the bacterium through its environment. The rotation is driven by the basal body, which utilizes energy derived from the proton motive force across the cell membrane.

**8. Flagellar Switching:**
Bacteria can switch the direction of flagellar rotation, allowing them to change direction and move in a more complex manner. This switching is mediated by a specialized protein called FliM.

**9. Flagellar Disassembly:**
In some cases, bacteria can disassemble their flagella. This disassembly process is often triggered by environmental changes, such as nutrient depletion or exposure to toxic substances.

The assembly of the bacterial flagellum is a remarkable example of cellular complexity and efficiency. This intricate process allows bacteria to navigate their environment, find food sources, and escape from predators.'
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Proteins (4)

Compounds (2)