COMPARISON OF PORE-FORMING PEPTIDES FROM PATHOGENIC AND NONPATHOGENIC ENTAMOEBA-HISTOLYTICA

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.