Flagellin

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Flagellin
Identifiers
SymbolFlagellin
SCOP2
1ucu / SCOPe / SUPFAM
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

Flagellins are a family of

daltons.[2][3] Flagellins are the principal component of bacterial flagella that have a crucial role in bacterial motility
.

The gene that encodes for flagellin has a different name in different bacterial species such as flaA (Helicobacter pylori for example), fliC, fljB.[4][1]

Structure

flagella
on the cell surface

The structure of flagellin is responsible for the

E. coli it is unfolded by the flagellar secretion chaperone FliS (P26608) during transport.[5] The filament is made up of eleven smaller "protofilaments", nine of which contains flagellin in the L-type shape and the other two in the R-type shape.[6]

The helical

C-termini of flagellin form the inner core of the flagellin protein, and is responsible for flagellin's ability to polymerize into a filament. The middle residues make up the outer surface of the flagellar filament. While the termini of the protein are quite similar among all bacterial flagellins, the middle portion is wildly variable and can be absent in some species. The flagellin domains are numbered from the helical core (D0/D1) to the outside (D2, ...); when viewed from the amino-acid sequence, D0/D1 appears on the two termini. Flagellin-like structural proteins are found in other portions of the flagellum, such as the hook (flgE; P75937), the rod at the base, and the cap at the top.[7]

The middle part of  E. coli (and related) flagellin, D3, displays a beta-folium fold and appears to maintain flagellar stability.[8]

Immune response

In mammals

TLR11.[11] Some bacteria are able to switch between multiple flagellin genes
in order to evade this response.

Flagellins contain a Toll-like receptor 5 (TLR5) epitope, a region recognized by the immune receptor TLR5. There are variations in the strength of flagellin binding and its ability to activate TLR5. Flagellins can be classified into three groups based on these characteristics: si-lent flagellins, evaders and stimulators. Silent flagellins bind to TLR5 but do not induce signaling. Evaders are incapable of binding and, consequently, do not trigger TLR5 activation. Stimulators exhibit variable binding capabilities to TLR5 yet possess the ability to activate TLR5.[12]

The propensity of the immune response to flagellin may be explained by two facts:

  • Flagellin is an extremely abundant protein in flagellated bacteria.
  • There exists a specific innate
    TLR5).[13]

In plants

In addition, a 22-amino acid sequence (flg22) of the conserved N-terminal part of flagellin is known to activate plant defence mechanisms.

Mitogen-activated-protein-kinases (MAPK) acts as downstream signalling compounds, leading ultimately to PAMP-triggered immunity in which more than 900 genes are up-/down-regulated upon flg22 treatment.[citation needed
]

Pre-stimulation with a synthetic flg22-peptide led to enhanced resistance against bacterial invaders.[18]

References

  1. ^ a b "Bacterial flagellin family". www.uniprot.org.
  2. ^ "MeSH Browser". meshb.nlm.nih.gov. Retrieved 29 February 2024.
  3. PMID 34299141
    .
  4. ^
    PMID 17118981
    .
  5. ^ Vonderviszt F, Keiichi N (2013). Structure, Function and Assembly of Flagellar Axial Proteins. Austin, TX: Madame Curie Bioscience Database.
  6. S2CID 31915502
    .
  7. PMID 29235079
    .
  8. S2CID 4416455
    .
  9. PMID 9000497
    .
  10. S2CID 21897008
    .
  11. PMID 26859749
    .
  12. ^ DOI: 10.1126/sciimmunol.abq7001
  13. PMID 22279566
    .
  14. PMID 24772109
    .
  15. PMID 10911994
    .
  16. S2CID 2818791
    .
  17. S2CID 90436989
    .
  18. S2CID 4332562
    .

External links
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