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). Translation is inhibited by translational regulator CsrA (at protein level) (PubMed:27353476). Interacts with FliS via its C-terminal domain (residues 537-576), interacts with FliW via its N-terminal domain (residues 1-44). May form a 3-way complex of flagellin, FliS and FliW simultaneously, in which FliS and FliW do not directly interact (By similarity). 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.