Untersuchungen zur O-GlcNAc Modifikation von Plasmodium falciparum dem Erreger der Malaria tropica

Background: Despite the huge and in parts very successfull global effort to eradicate malaria, it still is one of the most deadly infectious diseases. Therefore Plasmodium falciparum the disease causing parasite is a major target of medical research. Post-translational modifications (PTMs) constitute a huge group of chemical modifications that increase the complexity of the proteomes of living beings. PTMs have been discussed as potential anti-malarial drug targets due to their involvement in many cell processes. O-GlcNAcylation is a widespread PTM found in different organisms including P.falciparum. The aim of this study was to identify O-GlcNAcylated proteins of P. falciparum, to learn more about such modification process and to predict its possible funcional role in the Apicomplexans. Methods: The P. falciparum strain 3D7 was cultivated in erythrocytes, purified and the proteome checked for the O-GlcNAc-modification by using different methods. The level of UDP-GlcNAc, the donor of the sugar moiety for O-GlcNAcylation processes, was measured using high performance anion exchange chromatography (HPAEC). O-GlcNAcylated proteins were enriched and purified utilizing either click chemistry labelling or adsorption on succinyl-wheat germ agglutinin beads. Proteins were then identified by mass-spectrometry (nano-LC MS/MS). Results: While low, when compared to MRC-5 control cells, P. falciparum possesses its own pool of UDP-GlcNAc. By using proteomics methods, 13 O-GlcNAcylated proteins were unambiguously identified in late trophozoites (11 by click-chemistry and 6 by sWGA-beads enrichment; 4 being identified by the two approaches). These proteins are all part of pathways, functions and structures important for the parasite survival. By probing „clicked“ proteins using specific antibodies the heat shock protein (Hsp)70 and alpha-tubulin were identified as P. falciparum O-GlcNAc-bearing proteins. Cultivation of P. falciparum in presence of an inhibitor for the O-GlcNAc catalysis reduced the parasite growth. However the interaction effect was not significant. Conclusion: This is the first study exploring the O-GlcNAcylated proteins in P.falciparum. While the parasite O-GlcNAcome seems to be close to those of other species, the structural differences exhibited by the proteomes provides a glimpse of innovative therapeutic paths to fight malaria. Blocking biosynthesis of UDP-GlcNAc or inhibiting the O-GlcNAc catalysis could be other promising options to inhibit the life cycle of Plasmodium. The existence of O-GlcNAcylation in P. falciparum and therefore in Apicomplexa in general could help to unravel the phylum’s difficult taxonomic classification.