Isolation and partial characterization of Hsp90 from Candida albicans

Hsp90 is a stress-induced protein involved in many cellular processes including the regulation of signal transduction and steroid hormone response pathways in higher eukaryotic cells. Candida albicans hsp90 has a mass of 82 -Da and has previously been implicated as a virulence factor. A 47-kDa C-terminal fragment of Candida hsp90 is a target for an immune response to C. albicans infections. A C. albicans hsp90 specific polyclonal antibody was developed against a synthetic peptide containing a previously defined epitope of the 47-kDa fragment. This antibody was used to investigate the cellular localization and induction of hsp90 in the fungus. By means of cell surface protein extraction, hsp90 is shown to be localized on the cell surface as well as in the cytoplasm. On the cell surface, it appears only as an 82-kDa protein. In the cytoplasm, anti-hsp90 detected the 82-kDa protein as well as 72-kDa and 47-kDa bands on SDS-PAGE gels. The cytoplasmic protein bands were heat inducible and appeared to be estrogen induced as well, suggesting that C. albicans modulates hsp90 expression in response to environmental changes. Since the 82-kDa protein is also found on the surface of the cells, hsp90 may be directly involved in sensing environmental changes. It may also be important for recognition of its host or elements of the host immune system and antibody responses to the molecule and may therefore be useful for diagnostic or prognostic evaluation.