Galactofuranose has been characterized in glycoinositolphospholipid (GIPL) anchor-like structures having a glycerolipid or a ceramide, as in lipopeptidophosphoglycan (LPPG) of Trypanosoma cruzi, in the oligosaccharide core of lipopeptidophosphoglycan (LPG) of Leishmania species, and also modifying high-mannose chains of trypanosomatid glycoproteins. Galactofuranose is usually present linked beta 1-->3 to Man, either as a terminal non-reducing unit, like in LPPG, or in the middle of the oligosaccharide core, as in LPG. The presence in protozoan parasites of galactose in the furanose configuration is a feature which deserves further attention since the mammalian hosts do not appear to produce glycoconjugates containing this structural unit. For that reason, hosts produce antibodies against galactofuranose, which may turn out to be important in understanding the pathogenesis and in the development of diagnostic methods. The metabolic pathways involved in the attachment to or removal of galactofuranose from glycoconjugates have not yet been elucidated. This is an area of incipient research, but of growing importance, since it will foster the design of inhibitors which may prove to be useful for the treatment of disease.

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Differentiation of Trypanosoma cruzi trypomastigotes to amastigotes inside myoblasts or in vitro, at low extracellular pH, in the presence of [3 H]palmitic acid or [ 3 H]inositol revealed differential labeling of inositolphosphoceramide and phosphatidylinositol, suggesting that a remodeling process takes place in both lipids. Using 3 H-labeled inositolphosphoceramide and phosphatidylinositol as substrates, we demonstrated the association of at least five enzymatic activities with the membranes of amastigotes and trypomastigotes. These included phospholipase A 1 , phospholipase A 2 , inositolphosphoceramide-fatty acid hydrolase, acyltransferase, and a phospholipase C releasing either ceramide or a glycerolipid from the inositolphospholipids. These enzymes may be acting in remodeling reactions leading to the anchor of mature glycoproteins or glycoinositolphospholipids and helping in the transformation of the plasma membrane, a necessary step in the differentiation of slender trypomastigotes to round amastigotes. Synthesis of inositolphosphoceramide and particularly of glycoinositolphospholipids was inhibited by aureobasidin A, a known inhibitor of fungal inositolphosphoceramide synthases. The antibiotic impaired the differentiation of trypomastigotes at acidic pH, as indicated by an increased appearance of intermediate forms and a decreased expression of the Ssp4 glycoprotein, a characteristic marker of amastigote forms. Aureobasidin A was also toxic to differentiating trypomastigotes at acidic pH but not to trypomastigotes maintained at neutral pH. Our data suggest that inositolphosphoceramide is implicated in T. cruzi differentiation and that its metabolism could provide important targets for the development of antiparasitic therapies.

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Inositol phospholipids (IPL) from epimastigote forms of Trypanosoma cruzi have been investigated by metabolic labelling with [3H]palmitic acid and by GLC-MS analysis of the lipids obtained from non-labelled parasites. The IPL fraction was separated into phosphatidylinositol (PI) and inositol-phosphoceramide subfractions, the latter accounting for 80-85% of the total IPL. The neutral lipids released from the IPLs by PI-specific phospholipase C (PI-PLC) from Bacillus thuringiensis were analysed by silica-gel and reverse-phase TLC for the radioactive lipids and by GLC-MS for the non-radioactive samples. Ceramides containing dihydrosphingosine and sphingosine with C16:0 and C18:0 fatty acids were identified. The main component in the [3H]palmitic acid-labelled ceramides was palmitoyldihydrospingosine, while in the non-labelled sample the ceramides contained mainly sphingosine. This could reflect partial uptake of phospholipid from the medium. The PI contain both alkylacyl- and diacyl-glycerol lipids, with the ether lipid being more abundant. The latter was identified as 1-O-hexadecylglycerol esterified by C18:2 and C18:1 fatty acids. Interestingly, the same lipid had been identified in the anchor of the 1G7 glycoprotein of T. cruzi metacyclic forms.

The lipopeptidophosphoglycan from Trypanosoma cruzi is a glycosylated inositol-phosphoceramide isolated from epimastigotes at the stationary phase of growth (4-5 days). We have now purified two similar glycoinositolphospholipids (glycoinositolphospholipid A and glycoinositolphospholipid B) from epimastigotes after the second day of culture growth.[3H]Palmitic acid was incorporated into 1 -0-hexadecyl-2-0-palmitoylglycerol in glycoinositolphospholipid A and into ceramide in glycoinositolphospholipid B. The lipids were released by incubation with glycosylphosphatidylinositol-specific phospholipase C from Bacillus thuringiensis or by chemical methods. After alkaline hydrolysis, the lipids were analysed by GLCMS. In glycoinositolphospholipid A the resulting lipids corresponded to 1 -0-hexadecylglycerol and palmitic acid. The ceramide components in glycoinositolphospholipid B are sphinganine, palmitic acid and lignoceric acid. The oligosaccharides could be degraded by nitrous acid and further enzymic treatment showed that the two glycoinositolphospholipids isolated from I: cruzi share the common core structure of the glycosylphosphatidylinositol membrane anchors. The microheterogeneity was determined, as well as the substitution by galactose, and was mainly in the furanose configuration as was previously described for lipopeptidophosphoglycan. However, methylation analysis indicated that 20% of the galactose is in the pyranose form. Both glycoinositolphospholipids mainly differ in the lipid moiety.Trypanosoma cruzi, the agent of Chagas' disease (South American trypanosomiasis) has a complex life cycle between the mammalian host and the insect vector [l]. The infective trypomastigote circulates in the peripheral blood of vertebrate hosts and is capable of penetrating cells. Cell penetration is followed by differentiation to the dividing amastigote stage. The intracellular amastigotes differentiate back to trypomastigotes which lyse the host cells and invade other neighboring cells or return into the circulation. When parasites are ingested by the insect vector (reduviid) during a blood meal, the trypomastigotes differentiate into dividing epimastigotes in the insect midgut. In the hindgut, epimasti- with an additional Manal-2 linked to the last mannose residue of the glycosyIPtdIns-conserved core and antigenic galactofuranose terminal units (AEP represents aminoethylphosphonic acid) [8, 91. A characteristic feature of the lipopeptidophosphoglycan is the presence of AEP linked to the 6 position of the glucosamine residue. Interestingly, AEP is the C-P analog of ethanolamine phosphate which is the link to the protein in the known glycosylPtdIns anchors.The lipid component in lipopeptidophosphoglycan is a ceramide which could be released by glycosylphosphatidyl-

The protozoan parasite Trypanosoma cruzi, the agent of Chagas disease, has a large number of mucin molecules on its surface, whose expression is regulated during the life cycle. These mucins are the main acceptors of sialic acid, a monosaccharide that is required by the parasite to infect and survive in the mammalian host. A large mucin-like gene family named TcMUC containing about 500 members has been identified previously in T. cruzi. TcMUC can be divided into two subfamilies according to the presence or absence of tandem repeats in the central region of the genes. In this work, T. cruzi parasites were transfected with one tagged member of each subfamily. Only the product from the gene with repeats was highly O-glycosylated in vivo. The O-linked oligosaccharides consisted mainly of beta-d-Galp(1-->4)GlcNAc and beta-d-Galp(1-->4)[beta-d-Galp(1-->6)]-d-GlcNAc. The same glycosyl moieties were found in endogenous mucins. The mature product was anchored by glycosylphosphatidylinositol to the plasma membrane and exposed to the medium. Sera from infected mice recognized the recombinant product of one repeats-containing gene thus showing that they are expressed during the infection. TcMUC genes encode a hypervariable region at the N terminus. We now show that the hypervariable region is indeed present in the exposed mature N termini of the mucins because sera from infected hosts recognized peptides having sequences from this region. The results are discussed in comparison with the mucins from the insect stages of the parasite (Di Noia, J. M., D'Orso, I., Sánchez, D. O., and Frasch, A. C. C. (2000) J. Biol. Chem. 275, 10218-10227) which do not have variable regions.