In Bordetella pertussis, the infectious agent in childhood whooping cough, filamentous haemagglutinin (FHA) is a surface-exposed and secreted protein that acts as a major virulence attachment factor, functioning as both a primary adhesin and an immunomodulator to bind the bacterial to cells of the respiratory epithelium. The FHA molecule has a globular head that consists of two domains: a shaft and a flexible tail. Its sequence contains two regions of tandem 19-residue repeats, where the repeat motif consists of short beta-strands separated by beta-turns.
