Analysis of mannoproteins from blastoconidia and hyphae of Candida albicans with a common epitope recognized by anti-complement receptor type 2 antibodies.
Mannoproteins of approximately 50 kDa from blastoconidia and 60 kDa from hyphae of Candida albicans reacted in Western blots (immunoblots) with either a polyclonal rabbit antiserum (CA-7) or a monoclonal antibody (CA-A) to the C. albicans C3d-binding protein (complement receptor type 2). The glycosylated nature of these proteins was demonstrated by their reactivity with concanavalin A and by selective labeling with the biotin-hydrazide reagent following periodate oxidation. Differences in the oligosaccharides of these proteins were observed in regard to their reactivity with lectin-peroxidase reagents and sensitivity to glycosidases such as N-glycanase or endoglycosidase F (but not endoglycosidase H). The 60-kDa mannoprotein reacted with wheat germ agglutinin, while the 50-kDa mannoprotein did not. Treatment of the 60-kDa mannoprotein with the glycosidases mentioned above resulted in its conversion into a species of 40 to 45 kDa. Enzyme treatment had no obvious effect on the electrophoretic mobility of the 50-kDa species from blastoconidia. Both the 50- and 60-kDa glycoproteins remained immunoreactive after treatment with the glycosidases. Reactivities of the two mannoproteins to neuraminidase also differed. Finally, the 50-kDa (blastoconidia) and the 60-kDa (hyphae) mannoproteins were purified by using ion-exchange chromatography and electroelution. The purified proteins differed in net charge, the 60-kDa species having a more acidic pI. Functional activity of the purified mannoproteins was demonstrated, as each inhibited the rosetting of antibody-sensitized sheep erythrocytes conjugated with iC3b or C3d by hyphae. Thus, an epitope(s) common to both a mycelial and blastoconidial mannoprotein is associated with a structurally different oligosaccharide for each growth form.
Wadsworth
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Department of Microbiology and Immunology, Georgetown University School of Medicine, Washington, D.C. 20007.
Prasad
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Calderone
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D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000946:Antigens, Fungal / Q000032:analysis / Q000276:immunology* / Q000302:isolation & purification; D002176:Candida albicans / Q000737:chemistry*; D004229:Dithiothreitol / Q000494:pharmacology; D000939:Epitopes; D006023:Glycoproteins / Q000032:analysis; D037102:Lectins / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000032:analysis / Q000276:immunology* / Q000302:isolation & purification; D008970:Molecular Weight; D009439:Neuraminidase / Q000494:pharmacology; D011817:Rabbits; D017464:Receptors, Complement 3d / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000946:Antigens, Fungal; D000939:Epitopes; D006023:Glycoproteins; D037102:Lectins; D008562:Membrane Glycoproteins; D017464:Receptors, Complement 3d; C025363:mannoproteins; D009439:Neuraminidase; D004229:Dithiothreitol