Primary and secondary structure of the pore-forming peptide of pathogenic Entamoeba histolytica
A pore-forming peptide is implicated in the potent cytolytic activity of pathogenic Entamoeba histolytica. Using NH2-terminal sequence information of this peptide, the corresponding cDNA was isolated. The cDNA-deduced amino acid sequence revealed a putative signal peptide and a mature peptide of 77 amino acids including six cysteine residues. Computer-aided secondary structure analysis predicted that the peptide would be composed of four adjacent alpha-helices, and CD spectroscopy indicated an all alpha-helical conformation. The tertiary structure appears to be stabilized by three disulfide bonds; the pore-forming activity was not sensitive to heat but was lost in the presence of reducing agents. Sequence homology was found to the saposins and to surfactant-associated protein B, both mammalian polypeptides of similar size and secondary structure but of non-lytic function. In particular, the six cysteine residues were found to be conserved, suggesting a common motif for stabilizing a favourable tertiary structure. Compared with previously characterized toxic peptides also containing three disulfide bonds, the amoeba peptide may represent a distinct class of biologically active peptides.
Keywords: Amino Acid Sequence ; Animals ; Base Sequence ; Blotting ; Northern ; Blotting ; Southern ; Circular Dichroism ; DNA ; Protozoan/genetics/isolation & purification ; Entamoeba histolytica/*genetics ; Gene Library ; *Ion Channels ; Membrane Proteins/*chemistry/genetics ; Molecular Sequence Data ; Polymerase Chain Reaction/methods ; Protein Conformation ; *Protein Structure ; Secondary ; Protozoan Proteins/*chemistry/genetics ; RNA ; Protozoan/genetics/isolation & purification ; Recombinant Proteins/chemistry ; Sequence Homology ; Amino Acid
Department of Molecular Biology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
Record created on 2009-01-30, modified on 2016-08-08