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Characterization of a membrane pore-forming protein from Entamoeba histolytica
Abstract:
We describe the partial purification and characterization of a pore-forming material (PEM) from Entamoeba histolytica. The formation of ion channels by PFM was examined in three systems. (a) PFM depolarizes J774 macrophages and mouse spleen lymphocytes as measured by [3H]TPP+ uptake. (b) PFM induces rapid monovalent cation flux across the membrane of phosphatidylcholine-cholesterol vesicles. (c) PFM confers a voltage-dependent conductance to artificial planar bilayers, which is resolved as a summation of opening of individually conducting steps of 67 pS in 0.1 M KCl. Monomers of PFM are functional; however, a preferential aggregation occurs in the planar bilayer. Activity is pronase, trypsin, and heat sensitive and is stable between pH 5-8. PFM is not secreted by unstimulated amoebae but after exposure to the calcium ionophore A23187, concanavalin A, and E. coli lipopolysaccharide, 5-10% of the total cell content of PFM is released into the medium within 5-10 min. High-performance gel filtration results in an approximately 1,000-fold purification of PFM and gives an Mr of 30,000. This protein may play a role in the cytotoxicity mediated by E. histolytica.
Insights
Researchers purified a pore-forming material (PFM) from Entamoeba histolytica. This protein forms ion channels and may contribute to amoebic cytotoxicity.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Entamoeba histolytica is an enteric protozoan parasite.
- E. histolytica causes amoebiasis, a significant human disease.
- The mechanisms of E. histolytica pathogenesis are not fully understood.
Purpose of the Study:
- To partially purify and characterize a pore-forming material (PFM) from E. histolytica.
- To investigate the ion channel-forming properties of PFM.
- To explore the potential role of PFM in E. histolytica-mediated cytotoxicity.
Main Methods:
- Partial purification of PFM using high-performance gel filtration.
- Characterization of PFM's ion channel activity in J774 macrophages, mouse spleen lymphocytes, and artificial planar bilayers.
- Assessment of PFM's sensitivity to enzymes, heat, and pH.
- Quantification of PFM release from E. histolytica after stimulation.
Main Results:
- PFM was purified approximately 1,000-fold with an Mr of 30,000.
- PFM depolarizes immune cells and induces cation flux across vesicle membranes.
- PFM forms voltage-dependent ion channels in planar bilayers with single-channel conductance of 67 pS.
- PFM is sensitive to proteases and heat, stable between pH 5-8.
- PFM is released from E. histolytica upon stimulation with ionophore A23187, concanavalin A, and LPS.
Conclusions:
- PFM is a functional pore-forming protein from E. histolytica.
- PFM exhibits properties consistent with a role in host cell damage.
- PFM may be a key virulence factor contributing to E. histolytica pathogenesis.