What is "pilin"

n. Any of a class of fibrous proteins found in pilus structures in bacteria.

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.

Some pilin proteins are α+β proteins characterized by a very long N-terminal alpha helix. The assembly of these pili 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. The exact mechanism of assembly of these pili from monomers is not known, although chaperone proteins have been identified for some types of pilin. and specific amino acids required for proper pilus formation have been isolated.