Hookbasal

Hookbasal, or hook-basal body, is a term used in microbiology to describe the structural complex at the base of the bacterial flagellum. It refers to the combined assembly of the basal body, which anchors the flagellum in the cell envelope and functions as the motor, and the distal hook, a flexible connector that transmits torque to the flagellar filament.

Structure and components: The basal body spans the cell membranes and cell wall and includes rotor and stator elements that convert chemical energy into mechanical rotation. The hook is a short, curved protein polymer (coded by FlgE) that forms a universal joint to the filament. The hook-basal body interacts with rod components and with the flagellar export apparatus that assembles distal parts of the flagellum.

Function: The hook-basal body acts as the torque generator for bacterial motility. Rotation driven by the proton motive force (or sodium motive force in some species) causes the hook to transmit torque to the long helical filament, enabling flagellar rotation and bacterial swimming. Stator units regulate torque and rotation speed, and chemotactic signals influence direction by modulating the motor.

Assembly and regulation: Assembly proceeds in a defined order, beginning with the basal body and exporter, followed by rod and hook components, and finally the filament. Gene expression and assembly are coordinated by regulatory networks that respond to environmental cues, ensuring proper construction and function of the motor apparatus.

Occurrence and significance: The hook-basal body is found in many Gram-negative bacteria bearing flagella. It is essential for motility, which can influence colonization, nutrient acquisition, and, in some species, pathogenicity.

See also: Bacterial flagellum, flagellin, MotA/MotB stators, FlgE.