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Interactions between Toxoplasma gondii and its host cells: function of the penetration-enhancing factor of toxoplasma
Abstract:
A protein with a molecular weight of 70,000 to 150,000 which was extracted from merozoites of Toxoplasma gondii enhanced the host cell penetration of the merozoites. The optimal pH and temperature for penetration of merozoites coincided with those favoring the action of the penetration-enhancing protein. In addition, a dependence on Ca and Mg existed for penetration of merozoites, either in the presence or absence of this protein. No evidence was found that indicated that the enhancing effect on penetration elicited by the protein was due to increased phagocytic capacity of host cells (HeLa) or improved motility of the merozoites. Electron microscopy demonstrated that the protein, in high concentration, caused disruption of cytoplasmic membranes. In a 100-fold-lower concentration, which still caused a marked enhancement of penetration, no such effect was observed. However, the vacuoles surrounding the penetrated parasites seemed smaller than for merozoites penetrating in cultures to which no penetration-enhancing factor was given, and the membranes limiting the vacuoles demonstrated discontinuities more often. The penetration-enchancing effect of some known enzymes was studies. However, none of these enzymes seemed to correspond to the penetration-enhancing protein of toxoplasma. The mode of entry of toxoplasma merozoites into host cells is discussed. It is concluded that phagocytosis must play a less important role and that merozoites actively penetrate the cytoplasmic membranes of the host cells. The penetration is proposed to be a result of combined mechanical and chemical actions. It is suggested that an enzymatic function of the penetration-enhancing factor released by the merozoites is of importance. The membrane limiting the vacuole of a penetrated merozoite seems to be newly formed in the cell after penetration is completed.
Insights
A protein from Toxoplasma gondii merozoites enhances host cell invasion. This protein facilitates parasite entry, suggesting active penetration rather than phagocytosis, and may involve enzymatic activity.
Area of Science:
- Parasitology
- Cell Biology
- Molecular Biology
Background:
- Toxoplasma gondii merozoites invade host cells.
- The mechanism of host cell entry is not fully understood.
- Identifying factors that enhance parasite invasion is crucial for understanding pathogenesis.
Purpose of the Study:
- To identify and characterize a protein from Toxoplasma gondii merozoites that enhances host cell penetration.
- To elucidate the mechanism by which this protein facilitates merozoite entry.
- To investigate the role of host cell factors and parasite motility in the invasion process.
Main Methods:
- Protein extraction and purification from T. gondii merozoites.
- Host cell penetration assays using HeLa cells.
- Optimization of pH and temperature for protein activity.
- Electron microscopy to visualize parasite-host cell interactions.
- Enzyme activity assays.
Main Results:
- A protein (70-150 kDa) from T. gondii merozoites significantly enhanced host cell penetration.
- Optimal penetration conditions (pH, temperature) correlated with protein activity.
- Ca2+ and Mg2+ were essential for merozoite penetration, with or without the enhancing protein.
- The protein did not increase host cell phagocytosis or merozoite motility.
- High protein concentrations disrupted host cell membranes; lower concentrations enhanced penetration without membrane disruption.
- Vacuoles around penetrated parasites showed discontinuities and were smaller.
- No known enzymes corresponded to the identified penetration-enhancing protein.
Conclusions:
- Toxoplasma gondii merozoites actively penetrate host cell cytoplasmic membranes, with phagocytosis playing a minor role.
- A specific protein released by merozoites is important for active penetration, likely through combined mechanical and enzymatic actions.
- The protein's function may involve enzymatic activity, facilitating entry and potentially influencing vacuole formation during invasion.