Membrane glycoconjugates of procyclic Trypanosoma simiae and Trypanosoma congolense, members of the subgenus Nannomonas are immunologically similar and biochemically distinct




Mookherjee, Neeloffer

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The surface molecules (procyclins) of procyclic forms of African trypanosomes (Trypanosoma brucei spp.) are complex mixtures of lipid-anchored glycoconjugates. The procyclins are expressed differentially during the parasite life cycle within the tsetse fly vector. It has been hypothesised that these surface molecules are involved in interactions with molecules of the tsetse fly and may influence differentiation, cell death and tissue tropism. To understand procyclin functions it is necessary to identify and characterise them. This thesis presents a study of the biochemical and immunochemical characteristics of the major surface molecules of Trypanosoma simiae and Trypanosoma congolense, animal pathogens of the subgenus Nannomonas that share the same developmental cycle and tropism within the tsetse vector. Organic solvent extraction, reverse-phase high performance liquid chromatography and enzyme-linked imnunosorbent assay using surface binding monoclonal antibodies were used to isolate membrane molecules of procyclic culture forms (PCF) of both trypanosome species. Gel electrophoresis of the purified molecules revealed two predominant molecular species from each parasite that were broadly similar yet showed different apparent molecular masses and staining characteristics. The molecules were shown to be glycosylphosphatidylinositol-lipid anchored glycoconjugates, comprised mainly of carbohydrates. Each moiety displayed surface-disposed carbohydrate epitopes that were recognised on the surface of both species of trypanosomes by monoclonal antibodies specific for procyclic parasites of the subgenus Nannomonas. The epitopes were previously shown to be displayed on the glutamic acid-alanine rich protein (GARP) of T. congolense, yet neither this protein (as detected either immunologically or by mass spectrometry) nor its encoding gene (as detected by Southern blot analysis) was present in T. simiae. The results indicate that although T. congolense and T. simiae share common carbohydrate surface epitopes, these are displayed on biochemically different molecules. I hypothesise that the surface disposed carbohydrate structures and not the polypeptide moieties are involved in parasite-tsetse interactions since these species have the same developmental cycles in the insect vector. In an attempt to obtain primary sequence information for the T. simiae PCF surface molecules, I identified and characterised an unique open reading frame. This was shown to be expressed as a protein in PCF and is likely a membrane-associated molecule of the subgenus Nannomonas.



Trypanosoma, Immunogenetics, Tsetse-flies, Glycoconjugates