Analysis of cytoplasmic antigens of the yeast and mycelial phases of Candida albicans by two-dimensional electrophoresis

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Abstract
The extent of the macromolecular change accompanying yeast to mycelium morphogenesis of C. albicans was analyzed by 2-dimensional gel electrophoresis of the cytoplasmic proteins of the 2 growth forms after antibody cross-absorption experiments. Pure cultures of yeasts and true hyphae (i.e., without concomitant production of pseudohyphae) were grown in a synthetic low-sulfate medium (LSM). The 2 strains selected for this study were strain 4918, which produces pure mycelial (M) cultures in LSM at 37.degree. C (designated 4918-37M) and yeasts (Y) at 24.degree. C (4918-24Y), and strain 2252, which produces yeasts exclusively at 24 and 37.degree. C in LSM (2252-24Y and 2252-37Y). The proteins of both strains were labeled at both temperatures with [35S]sulfate and cytoplasmic fractions were prepared by mechanical disruption and ultracentrifugation. Rabbits were immunized with the 4918-24Y and 4918-37M cytoplasmic fractions to produce anti-yeast-phase and anti-mycelial-phase hyperimmune sera. Each radiolabeled cytoplasmic fraction was absorbed with anti-mycelial-phase Ig, anti-yeast Ig and Ig from normal rabbit serum. Staphylococcal protein A was used to remove immune complexes. The labeled, nonabsorbed proteins were analyzed by 2-dimensional electrophoresis. Highly reproducible protein spot patterns were obtained which defined hundreds of proteins in each extract. The specificity of the Ig preparations was extremely broad and as many as 168 cytoplasmic antigens were detected. Antigens (83) were recognized in the mycelial-phase extract only by the anti-mycelial-phase Ig. Comparative analysis revealed that all of these proteins were present in at least 1 other extract. None of them was unique to the mycelial morphology. Antigens (11) were detected in the 2252-37Y extract that were not present in the extracts from strain 4918, which indicates that proteins obtained from different strains may express similar antigenic determinants but differ in their physiochemical properties.