FlaB

FlaB refers to a family of flagellin B proteins encoded by flaB genes in several spirochete bacteria. These proteins are structural components of the periplasmic flagellum, the axial filament that resides between the inner and outer membranes of the cell and enables the characteristic corkscrew motility of spirochetes.

Most genomes of spirochetes carry multiple flaB genes, sometimes designated flaB1, flaB2, and so on. The encoded FlaB proteins assemble into the core of the periplasmic flagellum and interact with other flagellar components, such as FlaA, to form a functional axial filament. Variation among FlaB paralogs contributes to antigenic diversity and may reflect adaptation to different hosts or environmental conditions.

Expression of flaB genes is regulated by growth conditions and developmental stage, and the proteins are exposed to the host immune system, provoking antibody responses. In clinical contexts, FlaB proteins are among the antigens detected in serological tests for spirochete infections and have been studied as potential vaccine targets, though cross-reactivity and sequence diversity pose challenges.

Taxonomically, FlaB proteins are characteristic of spirochetes such as Borrelia, Leptospira, and Treponema, and are often studied to understand flagellar assembly, motility, and pathogenicity. Research continues to delineate the specific roles of different FlaB paralogs in motility, host interaction, and immune evasion.