What does flagellin mean?
Flagellin is a protein produced by many bacteria and serves as the chief building block of their flagella — the long, thread-like filaments that spin like propellers to drive the cells through liquid environments. Each bacterial flagellar filament consists of thousands of flagellin molecules arranged in a helix, and the remarkable precision of this self-assembly has made flagellin a model system for studying how proteins form complex structures. Beyond its structural role, flagellin is biologically significant because it is recognized by receptors of the innate immune system, notably Toll-like receptor 5 in mammals; its detection signals the presence of potentially harmful bacteria and triggers an inflammatory response. This dual identity — as both a molecular motor component and an immune trigger — makes flagellin valuable in research on vaccines, adjuvants, and host–pathogen interactions. The word appears chiefly in scientific contexts and derives from Latin flagellum, meaning 'whip'.
nounA globular protein that is the principal structural component of bacterial flagella, polymerizing to form the filament that rotates to propel the bacterium.
- The protein monomer that self-assembles into the helical filament of bacterial flagella, functioning as the propeller of motile bacteria.
"The immune system recognizes bacterial infections partly through Toll-like receptor 5, which detects the protein flagellin."
"Because flagellin varies between strains, microbiologists can use it to distinguish closely related Salmonella serovars."
"Vaccine designers have fused antigens to flagellin to exploit its strong activation of the innate immune system."
Used mainly when referring collectively to different flagellin variants or homologues across species or serotypes; the singular or mass-noun usage predominates in scientific writing.
"Different flagellins are expressed depending on whether the bacterium is in its swimming or swarming phase."
The same molecule that spins a bacterium's tail also trips your body's infection alarm — flagellin is both motor and red flag.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of flagellin
The term flagellin was formed from Latin flagellum, meaning 'whip', via the same combining element that gave English 'flagellum' and 'flagellate'. It arose within twentieth-century microbiology as researchers identified the protein subunits composing bacterial flagella. Its root traces back further to the Latin verb flagellare, 'to whip', making it a true cognate of words such as 'flagellation' and 'conflagration' in origin.
How flagellin is actually used
A technical term used almost exclusively in microbiology, immunology, and molecular biology; it is rarely encountered outside scientific literature and carries no informal register or figurative use.
Easily confused with flagellin
A flagellum is the entire whip-like appendage that propels a cell, whereas flagellin is the specific protein subunit of which that appendage's filament is built.
A flagellate is a single-celled organism bearing flagella, while flagellin is the structural protein found in bacterial flagella.