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Pilin (bacterial filament)
Pilin protein from Neisseria gonorrhoeae, a parasitic bacterium that requires functional pili for pathogenesis.
Symbol Pilin
Pfam PF00114
InterPro IPR001082
SCOP 1paj
OPM superfamily 74
OPM protein 2hil

Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. Bacterial pili are used in the exchange of genetic material during bacterial conjugation, while a shorter type of appendages also made up of pilin, called fimbriae, are used as a cell adhesion mechanism. Although not all bacteria have pili or fimbriae, bacterial pathogens often use their fimbriae to attach to host cells. In gram-negative bacteria, where pili are more common, individual pilin molecules are linked by noncovalent protein-protein interactions, while gram-positive bacteria often have polymerized pilin.[1]

Pilin proteins themselves are α+β proteins characterized by a very long N-terminal alpha helix. Many pilins are post-translationally modified by glycosylation or phosphorylation. The assembly of a complete pilus relies on interactions between the N-terminal helices of the individual monomers. The pilus structure sequesters the helices in the center of the fiber lining a central pore, while antiparallel beta sheets occupy the exterior of the fiber.[2] The exact mechanism of pilus assembly from monomers is not known, although chaperone proteins have been identified for some types of pilin.[3] and specific amino acids required for proper pilus formation have been isolated.[4]

Development of molecular tools[edit]

Pili in Gram-positive bacteria contain spontaneously formed isopeptide bonds. These bonds provide enhanced stability to the protein. Recently, the pilin protein from Streptococcus pyogenes has been split into two fragments to develop a new molecular tool called the isopeptag. [5] The isopeptag is a short peptide that can be attached to a protein of interest and can bind its binding partner through a spontaneously formed isopeptide bond. This new peptide tag can allow scientists to target and isolate their proteins of interest through a permanent covalent bond.


  1. ^ Telford JL, Barocchi MA, Margarit I, Rappuoli R, Grandi G. (2006). Pili in gram-positive pathogens. Nat Rev Microbiol 4(7):509-19.
  2. ^ Forest KT, Tainer JA. (1997). Type-4 pilus-structure: outside to inside and top to bottom—a minireview. Gene 192(1):165-9.
  3. ^ Jones CH, Pinkner JS, Nicholes AV, Slonim LN, Abraham SN, Hultgren SJ. (1993). FimC is a periplasmic PapD-like chaperone that directs assembly of type 1 pili in bacteria. Proc Natl Acad Sci USA 90(18):8397-401.
  4. ^ Mu XQ, Jiang ZG, Bullitt E. (2005). Localization of a critical interface for helical rod formation of bacterial adhesion P-pili. J Mol Biol 346(1):13-20.
  5. [6] Zakeri,B. and Howarth,M. (2010). Spontaneous intermolecular amide bond formation between side chains for irreversible peptide targeting. J. Am. Chem. Soc. 132, 4526-4527.