COMPARISON OF PORE-FORMING PEPTIDES FROM PATHOGENIC AND NONPATHOGENICENTAMOEBA-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-f orming peptide termed APnp was isolated from a nonpathogenic isolate u sing 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 A Pnp and APp, and secondary structure predictions revealed a high degre e of similarity. Notably, a glutamic acid residue at position 2 of APp is in APnp replaced by proline, which shortens one of the two amphipa thic alpha-helices considered crucial for the pore-forming function. T his structural divergence of the two peptides might explain the differ ence in their pore-forming activities.