The fungal pathogen Coccidioides posadasii is the causative agent for the human disease Valley Fever. The two morphologies of this organism are the soil-borne mycelia phase and the spherule phase in the lungs of the host animal. Proteins from the spherule cell wall are vaccine antigen candidates based on physical availability to host immune systems and association with a unique fungal feature not found in mammals. Many fungal vaccine candidates are highly expressed in the tissue phase of dimorphic pathogenic fungi and cell-wall associated. Thus, a comprehensive proteomic analysis of Coccidioides posadasii spherule cell wall proteins has begun. There are three classes of cell wall proteins, distinguished by chemical bonds to the cell wall, which will be extracted and identified by nano HPLC-MS/MS tandem mass spectrometry (MS/MS). Target vaccine candidates will be further analyzed for immunogenicity in mice.

We have identified three antigen targets from an aqueous spherule extract using two-dimensional fluorescence differential gel electrophoresis (2D-DIGE) and MS/MS. We also identified 54 proteins from an immunogenic fraction (GF-1) of a spherule cell wall extract using MS/MS. Two previously unexamined proteins appeared to possess characteristics of protective antigens. The first is a homolog of a Saccharomyces cerevisiae cell wall protein. A second previously unidentified protein is homologous only to a few hypothetical fungal proteins, but has an excretion signal sequence and mannose binding domain, placing it on the exterior of the cell. These proteins have been produced in a yeast expression system and will be tested for immunogenicity in mice.