Characterization of PIR 32, a candida albicans cell wall protein. (c2009)

Abstract

Candida albicans is a common opportunistic pathogen that causes a wide variety of diseases in a human immunocompromised host. C .albicans is the most common fungal pathogen retrieved from the blood as well as from superficial infection sites. In a pathogen, cell wall proteins are important for stability as well as for acting as antigenic determinants and virulence factors. This study has characterized Pir32, a C. albicans cell wall protein. Pir32 is a member of the Pir protein family previously shown to be upregulated in response to macrophage contact and whose other member, Pirl, was found to be necessary for cell wall rigidity. We have thus generated a pir32 homozygote null strain by the use of PCR generated cassettes that underwent homologous recombination at the native PIR32 ORF's. PIR32 is not an essential gene since a homozygous null was successfully generated. The homozygote null mutant was then subjected to a battery of tests to reveal the role that Pir32 plays. Our mutant was shown to be slightly hyperftlamentous, resistant to sodium dodecyl sulfate, hydrogen peroxide, sodium chloride, and more virulent in a mouse model when compared to the wild type. Also the mutant exhibited a slight yet significant deficiency in biofilm formation and showed a delay in adhesion to human epithelial cells. Pir32 however seems not to playa role in antifungal drug resistance, sensitivity to cell wall disrupting agents or involved in heat shock stress response. Our mutation seems to have strengthened the cell surface, rather than weakened it. This has rendered it more resistant to external stress factors. The question remains however as to what factors were upregulated in the mutant to compensate for the Pir32 deletion increasing the rigidity of the cell surface and thus opening the door to further experimentation.