Fungal fimbriae are composed of collagen.

Abstract

Fungal fimbriae are surface appendages that were first described on the haploid cells of the smut fungus, Microbotryum violaceum. They are long (1-20 microm), narrow (7 nm) flexuous structures that have been implicated in cellular functions such as mating and pathogenesis. Since the initial description, numerous fungi from all five phyla have been shown to produce fimbriae on their extracellular surfaces. The present study analyses the protein component of M.violaceum fimbriae. The N-terminus and three internal amino acid sequences were determined. All four show a strong similarity to sequences which are characteristic of the collagen gene family. Enzymatic digests and immunochemical analyses support this finding. Based on these results, it is suggested that the proteinaceous subunits of fimbriae should be termed fungal collagens. Previously, collagen has been found only among members of the kingdom Animalia where it is the principal component of the animal extracellular matrix and is the most abundant animal protein. The unexpected finding of collagen in the members of the Mycota suggests that it may have evolved from a common ancestor that existed before the divergence of fungi and animals. Further, native fungal fimbriae can function as a mammalian extracellular matrix component. They can act as a substratum which permits animal cells to adhere, spread, and proliferate in a manner similar to animal collagens. The implications of this finding to both phylogeny and pathology are discussed.