Identification of the Lipid Moiety and Further Characterization of the Novel Lipophosphoglycan-like Glycoconjugates of Trichomonas vaginalis and Trichomonas foetus

The lipid moiety of the lipophosphoglycan (LPG)-like glycoconjugates of Trichomonas vaginalis and Trichomonas foetus, parasites of the urogenital tract of human and cattle, respectively, has been isolated and characterized by a combination of enzymatic and chemical degradation, chromatography, and mass spectrometry. The carbohydrate composition of the glycan inositol lipid core is also reported. The glycan inositol core of trichomonad glycoconjugates is unique in having more than one GlcN and is significantly larger than any other glycan core reported so far. T. vaginalis glycoconjugate binds strongly to the lectin RCA-I, which suggest that the macromolecule possesses terminal β1,4-linked galactosyl residues. The binding of T. foetus glycoconjugate to the lectin UEA-I suggests the presence of terminal α1,2-linked fucose. Acid hydrolysis of deaminated and reduced LPG products yields a [3H] anhydromannitol-containing product, indicating the presence of unacetylated glucosamine in the trichomonad LPGs. Reductive radiomethylation has been applied to label free amino groups in the hexosamine or other free amine-containing residues of the trichomonad glycoconjugates. Treatment of the LPGs with phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis liberates a ceramide substituent. Treatment of LPGs with nitrous acid releases a phospholipid moiety containing myo-inositol and ceramide, implying that the LPGs are anchored in the membrane via an inositol-phosphate-ceramide. Structural characterization of the ceramide by gas-liquid chromatography (GC) and GC-mass spectrometry indicated the presence of the major long-chain base sphinganine (d 18: 0 dihydrosphingosine) and a C 16:0 N-acyl group. Lipophosphoglycans from both parasites contain ceramide as their only lipid moiety. These results suggest that T. vaginalis and T. foetus anchor their LPG-like glycoconjugates on the cell surface via inositol-phosphoceramide and also the glycan inositol core of the macromolecule appears to be unique in nature.