Protein profiling of the dimorphic, pathogenic fungus, Penicillium marneffei

<p>Abstract</p> <p>Background</p> <p><it>Penicillium marneffei </it>is a pathogenic fungus that afflicts immunocompromised individuals having lived or traveled in Southeast Asia. This species is unique in that it is the only dimorphic member of the genus. Dimorphism results from a process, termed phase transition, which is regulated by temperature of incubation. At room temperature, the fungus grows filamentously (mould phase), but at body temperature (37°C), a uninucleate yeast form develops that reproduces by fission. Formation of the yeast phase appears to be a requisite for pathogenicity. To date, no genes have been identified in <it>P. marneffei </it>that strictly induce mould-to-yeast phase conversion. In an effort to help identify potential gene products associated with morphogenesis, protein profiles were generated from the yeast and mould phases of <it>P. marneffei</it>.</p> <p>Results</p> <p>Whole cell proteins from the early stages of mould and yeast development in <it>P. marneffei </it>were resolved by two-dimensional gel electrophoresis. Selected proteins were recovered and sequenced by capillary-liquid chromatography-nanospray tandem mass spectrometry. Putative identifications were derived by searching available databases for homologous fungal sequences. Proteins found common to both mould and yeast phases included the signal transduction proteins cyclophilin and a RACK1-like ortholog, as well as those related to general metabolism, energy production, and protection from oxygen radicals. Many of the mould-specific proteins identified possessed similar functions. By comparison, proteins exhibiting increased expression during development of the parasitic yeast phase comprised those involved in heat-shock responses, general metabolism, and cell-wall biosynthesis, as well as a small GTPase that regulates nuclear membrane transport and mitotic processes in fungi. The cognate gene encoding the latter protein, designated <it>RanA</it>, was subsequently cloned and characterized. The <it>P. marneffei </it>RanA protein sequence, which contained the signature motif of Ran-GTPases, exhibited 90% homology to homologous <it>Aspergillus </it>proteins.</p> <p>Conclusion</p> <p>This study clearly demonstrates the utility of proteomic approaches to studying dimorphism in <it>P. marneffei</it>. Moreover, this strategy complements and extends current genetic methodologies directed towards understanding the molecular mechanisms of phase transition. Finally, the documented increased levels of RanA expression suggest that cellular development in this fungus involves additional signaling mechanisms than have been previously described in <it>P. marneffei</it>.</p

Biological Function and Molecular Mapping of M Antigen in Yeast Phase of Histoplasma capsulatum

Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody

Antifungal Activity and Molecular Mechanisms of Partial Purified Antifungal Proteins from Rhinacanthus nasutus against Talaromyces marneffei

Antifungal proteins (AFPs) are able to inhibit a wide spectrum of fungi without significant toxicity to the hosts. This study examined the antifungal activity of AFPs isolated from a Thai medicinal plant, Rhinacanthus nasutus, against the human pathogenic fungus Talaromycesmarneffei. This dimorphic fungus causes systemic infections in immunocompromised individuals and is endemic in Southeast Asian countries. The R. nasutus crude protein extract inhibited the growth of T. marneffei. The anti-T. marneffei activity was completely lost when treated with proteinase K and pepsin, indicating that the antifungal activity was dependent on a protein component. The total protein extract from R. nasutus was partially purified by size fractionation to ≤10, 10-30, and ≥30 kDa fractions and tested for the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC). All fractions showed anti-T. marneffei activity with the MIC and MFC values of 32 to 128 μg/mL and >128 μg/mL, respectively. In order to determine the mechanism of inhibition, all fractions were tested with T. marneffei mutant strains affected in G-protein signaling and cell wall integrity pathways. The anti-T. marneffei activity of the 10-30 kDa fraction was abrogated by deletion of gasA and gasC, the genes encoding alpha subunits of heterotrimeric G-proteins, indicating that the inhibitory effect is related to intracellular signaling through G-proteins. The work demonstrates that antifungal proteins isolated from R. nasutus represent sources for novel drug development