The cell surface of Trypanosoma cruzi

UDP-glycosyltransferase genes in trypanosomatid genomes have diversified independently to meet the distinct developmental needs of parasite adaptations

BACKGROUND

Trypanosomatid parasites such as Trypanosoma spp. and Leishmania spp. are a major source of infectious disease in humans and domestic animals worldwide. Fundamental to the host-parasite interactions of these potent pathogens are their cell surfaces, which are highly decorated with glycosylated proteins and other macromolecules. Trypanosomatid genomes contain large multi-copy gene families encoding UDP-dependent glycosyltransferases (UGTs), the primary role of which is cell-surface decoration. Here we report a phylogenetic analysis of UGTs from diverse trypanosomatid genomes, the aim of which was to understand the origin and evolution of their diversity.

RESULTS

By combining phylogenetics with analyses of recombination, and selection, we compared UGT repertoire, genomic context and sequence evolution across 19 trypanosomatids. We identified a UGT lineage present in stercorarian trypanosomes and a free-living kinetoplastid Bodo saltans that likely represents the ancestral state of this gene family. The phylogeny of parasite-specific genes shows that UGTs repertoire in Leishmaniinae and salivarian trypanosomes has expanded independently and with distinct evolutionary dynamics. In the former, the ancestral UGT repertoire was organised in a tandem array from which sporadic transpositions to telomeric regions occurred, allowing expansion most likely through telomeric exchange. In the latter, the ancestral UGT repertoire was comprised of seven subtelomeric lineages, two of which have greatly expanded potentially by gene transposition between these dynamic regions of the genome.

CONCLUSIONS

The phylogeny of UGTs confirms that they represent a substantial parasite-specific innovation, which has diversified independently in the distinct trypanosomatid lineages. Nonetheless, developmental regulation has been a strong driver of UGTs diversification in both African trypanosomes and Leishmania.

Glycolipid and protein profiles in trypanosomatids

A comparative study of glycolipid and protein composition in Trypanosoma cruzi and non-pathogenic trypanosomatids was carried out using Triton X-114 extraction. Protein profiles were analysed by polyacrylamide gel electrophoresis in sodium dodecyl sulphate (SDS-PAGE), and glycolipids were detected using high-performance thin-layer chromatography (HPTLC). Hydrophilic protein profiles were similar in non-pathogenic protozoa. Endotrypanum schaudinni, Crithidia luciliae and T. mega showed five characteristic protein bands ranging between 30 and 66 kDa. In the hydrophobic phase, a band of 50 kDa was present only in T. mega. Strain-specific protein distribution was detected in T. cruzi clone Dm28c and T. cruzi G and Y strains; clone Dm28c had five typical hydrophilic proteins at between 24 and 45 kDa, the G strain had two bands at 45 kDa in the hydrophilic phase and the Y strain had a major protein band at 24 kDa in both phases. T. dionisii and T. cruzi clone Dm28c showed a characteristic distribution of three hydrophilic proteins of approx. 45 kDa. Qualitative analysis of glycolipid composition showed that the T. cruzi strains and Dm28c clone and T. dionisii had four orcinol-positive spots, whereas in the other non-pathogenic trypanosomatids only three glycolipids were detected.

Anti-Trypanosoma-cruzi-proteinase antibodies and immunoprotection in experimental Chagas' disease

To verify whether anti-Trypanosoma-cruzi-proteinase antibodies are able to play a role in the development of Chagas' disease, CBA/J and C57BL/6 mice were immunized with purified proteinase fractions: antibody production was studied and passive immunization experiments were carried out. No significant differences were observed in the titre, isotype composition and specificity of the antibodies produced by the mouse strains. Immune sera produced in one strain was able to protect mice of both strains, provided that the challenge did not exceed the number of parasites corresponding to 30-fold the LD50. The data presented suggest that anti-proteinase antibodies may play a role in immunoprotection.

Trypanosoma cruzi: flow cytometric analysis of developmental stage differences in DNA

Flow cytometry and DNA binding-specific fluorescent reagents were used to compare the total DNA, G-C, and A-T content of the epimastigote and trypomastigote stages of Trypanosoma cruzi stocks. Significant total DNA differences of 2-12% between epimastigotes and trypomastigotes were found in three of six stocks studied. The epimastigote G-C content of five of six stocks was 4-8% higher than trypomastigotes, whereas the trypomastigote A-T content was 2.5-13% higher than the epimastigote A-T content. Although no obvious developmental stage association between total DNA and base composition was found, intrastage associations do exist. These observations were unaffected by nucleoprotein extraction implying that the observed differences between trypomastigotes and epimastigotes are not a consequence of nucleoprotein interference with DNA-binding fluorochromes. The nuclei and kinetoplasts of four T. cruzi stocks were isolated and analyzed. Developmental stage differences in nuclear and kinetoplast DNA are stock-dependent and base composition-dependent; both organelles contribute to the observed differences in DNA of intact cells. We found a nearly linear association between the percentage of total kinetoplast DNA, G-C, and A-T content. During metacyclogenesis, the G-C content decreases by approximately 7% as epimastigotes transform into metacyclic trypomastigotes. The decrease in G-C content precedes changes in morphology or in complement resistance. If the DNA changes are causally connected to developmental stage transformations in T. cruzi remains to be determined. However, our results could facilitate studies of the molecular genetic processes the parasite uses to successfully complete various phases of its life cycle and, consequently, the disease process it evokes.

Trypanosoma brucei brucei and Trypanosoma brucei gambiense: stage specific differences in wheat germ agglutinin binding and in endoglycosidase H sensitivity of glycoprotein oligosaccharides

Gel electrophoresis, lectin affinity blotting, and endoglycosidase H digestion have been used to analyze the glycoprotein profiles of bloodstream and procyclic forms of Trypanosoma brucei brucei and T. b. gambiense. Proteins resolved by polyacrylamide gel electrophoresis were stained with silver nitrate or electrophoretically transferred to nitrocellulose and probed with a horseradish peroxidase conjugate of either concanavalin A or wheat germ agglutinin. Silver staining showed, as expected, that the expression of the variant specific glycoprotein was restricted to the bloodstream forms. Twenty-three concanavalin A binding proteins were resolved in blots of bloodstream forms. Concanavalin A binding molecules corresponding in electrophoretic mobility to 21 of these 23 bloodstream form glycoproteins were detected in blots of procyclic forms. The two concanavalin A binding glycoproteins present only in bloodstream form extracts were variant specific glycoprotein and an 81-kDa protein designated glycoprotein 81b. One concanavalin A binding molecule of 84 kDa, glycoprotein 84p, was detected only in procyclic forms. The 19 major wheat germ agglutinin binding glycoproteins expressed by bloodstream forms were not detected in procyclic forms; only small proteins or protein fragments in procyclic form extracts bound wheat germ agglutinin. Incubating transferred proteins in endoglycosidase H eliminated subsequent binding of concanavalin A to most of the 22 common glycoproteins of bloodstream forms. Three major concanavalin A binding glycoproteins of bloodstream forms, variant specific glycoprotein, glycoprotein 81b, and a 110-kDa molecule (glycoprotein 110b), and other minor glycoproteins carried sugar chains that resisted endoglycosidase H digestion. In contrast, concanavalin A did not bind to any procyclic form glycoproteins, including a 110-kDa concanavalin A binding molecule (glycoprotein 110p) after endoglycosidase H treatment.(ABSTRACT TRUNCATED AT 250 WORDS)