Functional Characterization of Vacuolar ATP-Binding Cassette Transporters in Candida albicans
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ATP binding cassette transporters are a large family of integral membrane transport proteins which have vital functions in prokaryotic and eukaryotic organisms. The genome of Candida albicans, the most important opportunistic fungal pathogen in humans, harbors more than ten ABC transporter genes belonging to four ABC transporter subfamilies. In previous studies, we have characterized the Mlt1 ABC transporter, a member of the multidrug resistance-associated protein (MRP) subfamily of ABC transporters. Ycf1 (yeast cadmium factor 1), another member of this subfamily, initially was found in Saccharomyces cerevisiae sharing 42.6% identity with human MRP1. In this study we have begun to characterize the C. albicans orthologue of Ycf1 using gene disruption mutants and wild-type controls in cadmium and mercuric chloride susceptibility testing. Green fluorescent protein (GFP) fusion proteins were utilized to determine the cellular localization of the ABC transporter in C. albicans yeast and hyphal forms. Additionally, we use quantitative reverse transcriptase PCR to investigate ABC transporter gene expression. Our results indicate that the Ycf1 orthologue in C. albicans localizes to the vacuolar membrane of the fungi and appears to be involved in detoxification of cadmium and mercury, similar to the S. cerevisiae transporter. The gene expressions analyses revealed upregulation of the YCF1 mRNA during mercury exposure, further confirming the transporter's role in mercury detoxification. Future studies will focus on the role of Ycf1 in vacuolar function and inheritance of C. albicans as well as its involvement in virulence of this opportunistic pathogen.
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