Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Fungal fimbriae are surface appendages that were first described by Poon and Day (1974) on the haploid cells of Microbotryum violaceum. They are long (1 to 20 {dollar}\mu{dollar}m), narrow (7 nm) flexuous fibres that were implicated in important cellular functions such as mating and pathogenesis. Since this initial description, numerous other fungi from all five phyla have been shown to produce fimbriae on their extracellular surfaces. Because they are easy to purify, the fimbriae from M. violaceum have been investigated most extensively. The present study extends the earlier characterizations of M. violaceum fimbriae, and expands on the biochemical description of these unusual structures.;Fimbriae are complex structures that are shown here to be composed of three major components: protein, carbohydrate and RNA. The RNA component of fimbriae (f-RNA) is the first example of an extracellular RNA that has been well documented. It is a 30 base, single-stranded molecule that has a standard 5{dollar}\sp\prime{dollar} phosphate. The f-RNAs constitute a homogeneous population of macromolecules that are present in fimbriae isolated from both a{dollar}\sb1{dollar} and a{dollar}\sb2{dollar} mating types. f-RNA is abundant {dollar}(2.77\times10\sp3{dollar} f-RNA molecules per 1 {dollar}\mu{dollar}m fimbrial length) and well-protected. The existence of this extracellular f-RNA suggests intriguing possible mechanisms that may exist for cell to cell communication.;The structural subunit of M. violaceum fimbriae is a 74 kDa glycoprotein. The carbohydrate component is a 'high mannose type' that is covalently linked to an asparagine residue on the 47 kDa aglycone via two N-acetylglucosamine residues. Unlike the protein epitopes which are conserved in at least four fungal divisions, the carbohydrate component of fimbriae is order specific and can be used to distinguish between members of the fungal orders Microbotryales and Ustilaginales.;The protein component of M. violaceum fimbriae was also analyzed extensively. The N-terminus and three internal amino acid sequences show a strong similarity to a single gene family, the collagens. Further, enzymatic digests and immuno-chemical analyses support this finding. Based on these results, it is suggested that the proteinaceous subunits of fimbriae should be termed fungal collagens. Fungal collagens may be examples of orthologous evolution. Thus collagen, the principal component of the animal extracellular matrix, may have evolved in a common ancestor that existed prior to the divergence of fungi and animals.;Finally, native fimbriae can function as mammalian extracellular matrix components. In particular, fimbriae can act as a substratum, permitting animal cells to adhere, spread, and proliferate.;It is concluded that fimbriae are multifarious structures, much more elaborate than was initially reported. Each of the components, the f-RNA, the carbohydrate, and the fungal collagen, has its own individual intricacies and the biochemistry of each is fascinating. However, the role of native fimbriae in vivo remains elusive. Possible functions are discussed.



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