Flagellin is a protein that forms the structural basis of bacterial flagella, which are long, whip-like appendages that enable bacteria to move. It is a key component of the flagellar filament, allowing bacteria to swim through liquids. In addition to its role in motility, flagellin can also trigger immune responses in hosts. When recognized by the immune system, it can activate pathways that lead to inflammation, helping the body respond to bacterial infections. This dual role makes flagellin an important subject of study in microbiology and immunology.