title: Characterization of two novel cryptococcal mannoproteins recognized by immune sera.
abstract: Host defenses against the encapsulated yeast Cryptococcus neoformans involve both humoral and cell-mediated immunity. Mannoproteins (MPs) are a heterogeneous class of immunodominant glycoproteins which have been only incompletely characterized. In this study, we report on the molecular features of two novel MPs that are recognized by serum antibodies during cryptococcosis. After fractionation of extracellular cryptococcal products, MPs reacted more strongly than other components with sera from C. neoformans-infected AIDS patients. Further fractionation and Western blot analysis of MPs evidenced the presence of highly reactive bands with molecular masses of 250, 125, 115, and 84 kDa. The 115- and 84-kDa bands contained significant amounts of N-linked oligosaccharides, as shown by decreased molecular mass after peptide-N-glycosidase F treatment. N-terminal amino acid sequences of the two bands were used to search C. neoformans nucleotide databases. Homologous genomic sequences were used to synthesize DNA probes and isolate cDNA clones containing the full-length genes, which were designated MP84 and MP115. Both genes showed the presence of a serine/threonine-rich region, a potential site for heavy glycosylation. MP84 and MP115 showed homology with, respectively, polysaccharide deacetylases and carboxylesterases from other organisms. Recombinant, deglycosylated proteins expressed in Escherichia coli still reacted with sera from patients, albeit more weakly than natural MPs, indicating that at least some of the reactive epitopes were retained in the recombinant forms. In conclusion, we identified two novel MPs that are important targets of antibody responses during cryptococcosis. These data may be useful to devise alternative immunity-based strategies to control the disease.
authors.affiliation: Department of Pathology and Experimental Microbiology, University of Messina, Messina, Italy.
authors.forename: Carmelo
authors.initials: C
authors.lastname: Biondo
authors.forename: Luciano
authors.initials: L
authors.lastname: Messina
authors.forename: Mauro
authors.initials: M
authors.lastname: Bombaci
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Mancuso
authors.forename: Angelina
authors.initials: A
authors.lastname: Midiri
authors.forename: Concetta
authors.initials: C
authors.lastname: Beninati
authors.forename: Valentina
authors.initials: V
authors.lastname: Cusumano
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Gerace
authors.forename: Salvatore
authors.initials: S
authors.lastname: Papasergi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Teti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000908:Antibodies, Fungal / Q000276:immunology*; D000946:Antigens, Fungal / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D003001:Cloning, Molecular; D003453:Cryptococcosis / Q000276:immunology; D003455:Cryptococcus neoformans / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D005260:Female; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007106:Immune Sera / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D000908:Antibodies, Fungal; D000946:Antigens, Fungal; D005656:Fungal Proteins; D007106:Immune Sera; D008562:Membrane Glycoproteins; C025363:mannoproteins