Flagellin is the subunit protein which polymerizes to form the filaments of bacterial flagella. Heteromer of FlaA and FlaB (Probable). Interacts with FliW (PubMed:27353476). Interacts with FliS (PubMed:27353476). In a double flaA-flaB deletion, cells grow faster and are non-motile, flagellar filaments are non-existent (PubMed:27353476). Belongs to the bacterial flagellin family.