Fungal dimorphism is an interesting process by which some multicellular fungi can become unicellular pathogens. The increased incidence of infections by Penicillium marneffei, itself a dimorphic pathogen, have made this fungus the third leading cause of death due to AIDS-related illnesses in Thailand. The genetic basis of its temperature-dependent dimorphic-switch trigger has yet to be identified.
This study analyzed the protein profile of P. marneffei during phase-switch experiments in which four cultures were initially grown at both the mycelial (25°C) and yeast (37°C) temperatures for 12 hours. Subsequently, two of these cultures were switched to the other temperature for the remaining 12 hours (25°C to 37°C, and 37°C to 25°C). The proteins were isolated from each 24-hour culture and separated by two- dimensional gel electrophoresis. Differentially expressed protein spots were excised for mass spectrometry analysis to determine their amino acid sequence.
Three proteins stood out with respect to their high levels of expression in the 37°C (yeast) phase and 25°C-37°C switch phase. One, Hsp30 (Penicillium marneffei), is a molecular chaperone linked to the heat-shock response, and has been previously identified as a potential human antigen. The second, a synaptobrevin/VAMP-like protein (Debaryomyces hansenii CBS767), is likely to be highly involved in intracellular vesicle trafficking during the morphological change. And the third, an aldo-keto reductase (Phaeosphaeria nodorum SN15), has been indicated in the heat-shock response in other dimorphic fungi. These collective results open possible doors for cloning differentially expressed genes, the development of a pharmaceutical agent to slow infection, or elucidate the gene(s) involved in the dimorphic switch.