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Infection and Immunity, November 2005, p. 7348-7355, Vol. 73, No. 11
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.11.7348-7355.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Characterization of Two Novel Cryptococcal Mannoproteins Recognized by Immune Sera

Carmelo Biondo,1 Luciano Messina,1 Mauro Bombaci,1 Giuseppe Mancuso,1 Angelina Midiri,1 Concetta Beninati,1 Valentina Cusumano,2 Elisabetta Gerace,1 Salvatore Papasergi,1 and Giuseppe Teti1*

Department of Pathology and Experimental Microbiology, University of Messina, I-98125 Messina, Italy,1 VII Department of Infectious Diseases, Cotugno Hospital, I-80131 Naples, Italy2

Received 13 May 2005/ Returned for modification 6 July 2005/ Accepted 15 July 2005

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.

* Corresponding author. Mailing address: Policlinico Universitario, Via C. Valeria 1, I-98125 Messina, Italy. Phone: 39-090-221-3310. Fax: 39-090-221-3312. E-mail: teti{at}eniware.it.

Editor: T. R. Kozel

Infection and Immunity, November 2005, p. 7348-7355, Vol. 73, No. 11
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.11.7348-7355.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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