Structure determination of phosphoinositol oligosaccharides from parasitic protozoa using fast atom bombardment mass spectrometry

Structural variation in the glycoinositolphospholipids of different strains of Trypanosoma cruzi

The structures of the glycoinositolphospholipids (GIPLs) from five strains of the protozoan parasite Trypanosoma cruzi have been determined. Two series of structures were identified, all but one containing the same Man4(AEP)GlcN-Ins-PO4 core. Series 1 oligosaccharides are substituted at the third mannose distal to inositol (Man 3) by ethanolamine-phosphate or 2-aminoethylphosphonic acid, as are some glycosyl-phosphatidylinositol-protein anchors of T. cruzi. The core can be further substituted by terminal (1-3)-linked beta-galactofuranose units. In contrast, Series 2 oligosaccharides do not have additional phosphorus-containing groups attached to Man 3, the latter being substituted instead by a single side chain unit of beta-galactofuranose. Series 1 oligosaccharides are present in all strains (G, G-645, Tulahuen CL, and Y) whereas Series 2 structures are present mainly in CL and Y strains. The lipid moiety in the GIPLs from the G, G-645 and Tulahuen strains is predominantly ceramide, as reported for the Y strain, whilst that from the CL strain is a mixture of ceramide and alkylacylglycerol species. The lipid moiety of the GIPLs, and probably also the phosphoinositol-oligosaccharide structures may play an important immunomodulatory role in infection by T. cruzi.

Structural characterization of the major glycosylphosphatidylinositol membrane-anchored glycoprotein from epimastigote forms of Trypanosoma cruzi Y-strain

We have investigated the structure of the glycosylphosphatidylinositol (GPI) anchor and the O-linked glycan chains of the 40/45-kDa glycoprotein from the cell surface of the protozoan parasite Trypanosoma cruzi. This glycoconjugate is the major acceptor for sialic acid transferred by trans-sialidase of T. cruzi Y-strain, epimastigote form. The GPI anchor was liberated by treatment with hot alkali, and the phosphoinositol-oligosaccharide moiety was characterized and shown to have the following structure. [formula: see text] Unusually the glucosamine was 6-O-substituted with 2-aminoethylphosphonate, and 2-aminoethylphosphonate was also present on the third mannose residue distal to glucosamine, partially replacing the ethanolamine phosphate. The beta-eliminated reduced oligosaccharide chains showed that two novel classes of O-linked N-acetylglucosamine oligosaccharide were present. The first series had the structures Galp beta 1-3GlcNAc-ol; Galp beta 1-6(Galp beta 1-3)GlcNAc-ol; and Galp beta 1-2Galp beta 1-6(Galp beta 1-3)GlcNAc-ol, whereas the other series had a 1-4 linkage to N-acetylglucosaminitol and had structures Galp beta 1-4GlcNAc-ol, Galp beta 1-6(Galp beta 1-4)GlcNAc-ol, and Galp beta 1-2Galp beta 1-6(Galp beta 1-4)GlcNAc-ol. We have also investigated the kinetics of in vitro sialylation of these O-linked oligosaccharides by the T. cruzi transsialidase and have shown that incorporation of one molecule of sialic acid hinders entry of a second molecule when two potential acceptor sites are present.