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Toxoplasma gondii: uptake of fetuin and identification of a 15-kDa fetuin-binding protein
U Gross1, C Hambach, T Windeck
1Institute of Hygiene and Microbiology, University of Würzburg, Germany.
Abstract:
Lectin-binding studies demonstrated the presence of a 68-kDa glycoprotein in tachyzoites of Toxoplasma gondii harvested from P388D1 macrophage cell cultures but not in tachyzoites maintained in peritoneal cavities of NMRI mice. This protein was identified as the embryonic protein fetuin that regularly is contained in fetal calf serum, a component of cell-culture media. Uptake of fetuin by T. gondii was demonstrated by intracellular localization of this protein. As shown by latex agglutination and immunofluorescence, no specific binding of fetuin to the parasite's surface was detected. Using affinity chromatography on fetuin-agarose, it was demonstrated that fetuin bound specifically to a 15-kDa antigen of tachyzoites. As revealed by inhibition studies with sialic acid and the lectin Sambucus nigra agglutinin, the 15-kDa protein probably recognized glycan structures of fetuin.
Insights
Toxoplasma gondii tachyzoites internalize fetuin from cell culture media. A 15-kDa parasite antigen recognizes fetuin
Area of Science:
- Parasitology
- Molecular Biology
- Cell Biology
Background:
- Toxoplasma gondii tachyzoites are the rapidly replicating stage responsible for acute infection.
- Parasite-host interactions are crucial for T. gondii survival and pathogenesis.
- Components of cell culture media can be incorporated by parasites, potentially influencing their biology.
Purpose of the Study:
- To investigate the presence and origin of a 68-kDa glycoprotein in T. gondii tachyzoites.
- To identify the interaction between T. gondii tachyzoites and the identified glycoprotein.
- To characterize the molecular basis of this interaction.
Main Methods:
- Lectin-binding studies on tachyzoites from cell culture and mouse peritoneal cavities.
- Identification of the glycoprotein using protein analysis and comparison with cell culture components.
- Intracellular localization studies to confirm uptake.
- Latex agglutination and immunofluorescence assays to assess surface binding.
- Affinity chromatography and inhibition studies (sialic acid, Sambucus nigra agglutinin) to identify interacting parasite antigens and molecular recognition.
Main Results:
- A 68-kDa glycoprotein, identified as fetuin from fetal calf serum, was present in tachyzoites cultured in vitro but absent in those from mice.
- Fetuin was found intracellularly within tachyzoites, indicating uptake.
- No specific surface binding of fetuin was observed.
- Affinity chromatography revealed specific binding of fetuin to a 15-kDa tachyzoite antigen.
- Inhibition studies suggest the 15-kDa antigen recognizes glycan structures on fetuin, likely involving sialic acid.
Conclusions:
- Toxoplasma gondii tachyzoites actively internalize fetuin from their cell culture environment.
- A specific 15-kDa parasite antigen mediates the recognition and uptake of fetuin.
- This interaction highlights the parasite's ability to scavenge host or media-derived molecules, potentially impacting its biology in vitro.