Structure Elucidation of Sphingolipids from the Mycopathogen Paracoccidioides brasiliensis:  An Immunodominant β-Galactofuranose Residue Is Carried by a Novel Glycosylinositol Phosphorylceramide Antigen

Two major acidic glycolipid components (Pb-1 and Pb-2) have been extracted from the mycopathogen Paracoccidioides brasiliensis, a thermally dimorphic fungus endemic to rural areas of South and Central America. Sera of all patients exhibiting paracoccidioidomycosis were found to be reactive with Pb-1, but not with Pb-2; no reactivity was observed with sera of healthy patients or those with histoplasmosis [Toledo, M. S., Suzuki, S., Straus, A. H., and Takahashi, H. K. (1995) J. Med. Vet. Mycol. 33, 247−251]. We report here the complete structure elucidation of both P. brasiliensis glycolipids using monosaccharide, fatty acid, sphingosine, and inositol component analysis by GC-MS; 1H- and 31P NMR spectroscopy; ESI-MS and -MS/CID-MS, linkage analysis, and exoglycosidase digestion. The compounds were found to be glycosylinositol phosphorylceramides (GIPCs) with the following structures: Pb-2, Manpα1→3Manpα1→2Ins1-P-1Cer; and Pb-1, Manpα1→3[Galfβ1→6]Manpα1→2Ins1-P-1Cer. The serologically nonreactive Pb-2 appears to be a biosynthetic intermediate between mannosylinositol phosphorylceramide (MIPC), which is widely distributed among fungi, and the antigenic Pb-1. Pb-1 is a novel glycosphingolipid, similar to a triglycosyl IPC (Hc-VI) reported from Histoplasma capsulatum [Barr, K., Laine, R.A, and Lester, R. L. (1984) Biochemistry 23, 5589−5596], but differing in the anomeric configuration of the terminal Galf1→6 residue, which is immunodominant. The significance of these structures as serological and taxonomic markers, as well as their potential utility as targets for immunodiagnostic agents, is discussed.