Pilin

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, and a short pilus called a fimbrium is 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 pilinref|Telford.

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 fiberref|Forest. The exact mechanism of pilus assembly from monomers is not known, although chaperone proteins have been identified for some types of piliref|Jones and specific amino acids required for proper pilus formation have been isolatedref|Mu.

External links

* [http://scop.mrc-lmb.cam.ac.uk/scop/data/scop.b.e.ed.A.html SCOP Pili subunit fold]
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References

# Telford JL, Barocchi MA, Margarit I, Rappuoli R, Grandi G. (2006). Pili in gram-positive pathogens. "Nat Rev Microbiol" 4(7):509-19.
# Forest KT, Tainer JA. (1997). Type-4 pilus-structure: outside to inside and top to bottom--a minireview. "Gene" 192(1):165-9.
# 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.
# 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.