Pilin
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Pilin protein from Neisseria gonorrhoeae, a parasitic bacterium that requires functional pili for pathogenesis.

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 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 pili^[3] and specific amino acids required for proper pilus formation have been isolated^[4].

External links

• SCOP Pili subunit fold
• UMich Orientation of Proteins in Membranes protein/pdbid-2pil

References

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.

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