GLYCOSYLATION REACTIONS IN PLASMODIUM-FALCIPARUM, TOXOPLASMA-GONDII, AND TRYPANOSOMA-BRUCEI-BRUCEI PROBED BY THE USE OF SYNTHETIC PEPTIDES

Synthetic peptides were used to probe O- and N-glycosylation reactions in cell-free systems of the parasitic protozoa Plasmodium falciparum, Toxoplasma gondii, and Trypanosoma brucei brucei. O-Glycosylation of the peptide Pro-Tyr-Thr-Val-Val was observed with lysates from all org anisms. However, the spectrum of sugars transferred from their respect ive nucleotide or dolichol-phosphate derivatives to the peptide varied greatly according to the parasite. N-glycosylation of the peptides N- Bz-Asn-Gly-ThrNH(2) and DNP-Arg-Asn-Ala-Thr-Ala-ValNH(2) by exogenous radioactive dolichol-pyrophosphate linked oligosaccharide donors was o bserved only when lysates of T. gondii or T. b. brucei were used, but not in P. falciparum. To assay for endogenous N-glycosylation donors, the radiolabeled tripeptide [H-3]Ac-Asn-Gly-ThrNHMe was used as accept or. The peptide was N-glycosylated only by T. gondii and T. b. brucei preparations. Only in these latter two parasites dolichol-cycle mannos yltransferase activity was demonstrated by the elongation of exogenous radiolabeled dolichol-PP-chitobiose. The data substantiate the occurr ence of protein O-glycosylation in parasitic protozoa and the exceptio nal absence of protein N-glycosylation in the asexual intraerythrocyti c stage of the malaria parasite, P. falciparum.