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Comparison of pore-forming peptides from pathogenic and nonpathogenic Entamoeba histolytica
Abstract:
Similar to the findings obtained with pathogenic Entamoeba histolytica, nonpathogenic isolates were found to kill mammalian cells in vitro, and cell extract caused pore formation in liposome membranes. A pore-forming peptide termed APnp was isolated from a nonpathogenic isolate using the schedule developed for the purification of APp or amoebapore, the homologous peptide of the pathogenic isolate HM-1:IMSS. Compared to APp, the specific activity of APnp in pore formation was 60% lower. cDNA sequencing indicated 95% identity of the primary structures of APnp and APp, and secondary structure predictions revealed a high degree of similarity. Notably, a glutamic acid residue at position 2 of APp is in APnp replaced by proline, which shortens one of the two amphipathic alpha-helices considered crucial for the pore-forming function. This structural divergence of the two peptides might explain the difference in their pore-forming activities.
Insights
Nonpathogenic Entamoeba histolytica produces a pore-forming peptide, APnp, with lower activity than its pathogenic counterpart, APp. Structural differences, particularly a proline substitution, explain this reduced pore formation.
Area of Science:
- Cell Biology
- Biochemistry
- Parasitology
Background:
- Pathogenic Entamoeba histolytica causes amoebiasis, a significant human disease.
- Both pathogenic and nonpathogenic Entamoeba histolytica strains can lyse mammalian cells in vitro.
- Cell extracts from these amoebas induce pore formation in lipid bilayers.
Purpose of the Study:
- To isolate and characterize a pore-forming peptide from nonpathogenic Entamoeba histolytica.
- To compare the pore-forming activity and structure of this peptide with its homolog from pathogenic strains.
Main Methods:
- Isolation of a pore-forming peptide (APnp) from nonpathogenic Entamoeba histolytica using established purification protocols.
- Assay of pore formation activity in liposome membranes.
- cDNA sequencing and secondary structure prediction to analyze peptide structure.
Main Results:
- A pore-forming peptide, APnp, was successfully isolated from nonpathogenic Entamoeba histolytica.
- APnp exhibited 60% lower specific pore-forming activity compared to APp (amoebapore) from pathogenic strains.
- cDNA sequencing revealed 95% primary structure identity between APnp and APp, with significant secondary structure similarity.
- A key difference was identified: a proline residue at position 2 in APnp replaces glutamic acid in APp, potentially affecting amphipathic alpha-helices.
Conclusions:
- Nonpathogenic Entamoeba histolytica possesses a pore-forming peptide, APnp, homologous to amoebapore (APp).
- Structural variations, specifically the proline substitution in APnp, are likely responsible for its reduced pore-forming activity.
- These findings contribute to understanding the molecular mechanisms differentiating pathogenic and nonpathogenic Entamoeba histolytica.