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The pore-forming peptide of Entamoeba histolytica, the protozoan parasite causing human amoebiasis
M Leippe1, H J Müller-Eberhard
1Department of Molecular Biology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
Abstract:
Amoebapore, the pore-forming peptide of E. histolytica has been isolated and its structure elucidated on the cDNA and protein level. The peptide is composed of 77 amino acid residues including six cysteine residues and has a molecular mass of 8244 Da. The primary translation product contains a signal sequence of 21 mostly hydrophobic amino acid residues. The active peptide has been located in the cytoplasmic granules of the amoebae. Circular dichroism spectroscopy revealed an all alpha-helical conformation and computer-aided secondary structure prediction yielded a structure of four helices. The helical conformation and three intramolecular disulfide bonds impart a highly compact and rigid structure upon the molecule. The activity of amoebapore, measured by a liposome depolarization assay, is resistant to heating at 100 degrees C in the absence of reducing agents. Synthetic peptides corresponding to the helices 1 and 3 exhibited pore-forming activity. Two minor, biologically active isoforms of amoebapore have amino acid sequence identity of 57% and 47%, respectively. Whereas amoebapore is a constituent of pathogenic E. histolytica isolates, nonpathogenic E. histolytica produce a structurally very similar peptide, the specific activity of which is approximately one third that of amoebapore. The biological significance of amoebapore for the pathogenicity of E. histolytica and specifically for its cytolytic activity remains to be determined.
Insights
Amoebapore, a pore-forming peptide from E. histolytica, has an alpha-helical structure and is heat-resistant. Its role in pathogenicity is under investigation, with isoforms and related peptides identified.
Area of Science:
- Biochemistry
- Molecular Biology
- Parasitology
Background:
- Amoebapore is a pore-forming peptide identified in Entamoeba histolytica.
- Understanding its structure and function is crucial for elucidating E. histolytica pathogenicity.
Purpose of the Study:
- To isolate and characterize amoebapore from E. histolytica.
- To determine the structural features and functional activity of amoebapore.
- To investigate the relationship between amoebapore structure and pathogenicity.
Main Methods:
- Peptide isolation and structural elucidation using cDNA and protein analysis.
- Circular dichroism spectroscopy and computational secondary structure prediction.
- Liposome depolarization assay to measure pore-forming activity.
Main Results:
- Amoebapore is a 77-amino acid peptide with a molecular mass of 8244 Da, featuring six cysteine residues.
- It adopts a stable, compact, all alpha-helical conformation, predicted to have four helices.
- The peptide exhibits heat resistance and pore-forming activity, with synthetic helices 1 and 3 being active; isoforms and related peptides were identified.
Conclusions:
- Amoebapore possesses a well-defined, rigid alpha-helical structure stabilized by disulfide bonds.
- Its pore-forming activity is robust and potentially linked to E. histolytica's cytolytic capabilities.
- Further research is needed to confirm amoebapore's precise role in the pathogenicity of E. histolytica.