FUSOGENIC PROPERTIES OF THE C-TERMINAL DOMAIN OF THE ALZHEIMER BETA-AMYLOID PEPTIDE

A series of natural peptides and mutants, derived from the Alzheimer b eta-amyloid peptide, was synthesized, and the potential of these pepti des to induce fusion of unilamellar lipid vesicles was investigated. T hese peptide domains were identified by computer modeling and correspo nd to respectively the C-terminal (e.g. residues 29-40 and 29-42) and a central domain (13-28) of the beta-amyloid peptide. The C-terminal p eptides are predicted to insert in an oblique way into a lipid membran e through their N-terminal end, while the mutants are either parallel or perpendicular to the lipid bilayer. Peptide induced vesicle fusion was demonstrated by several techniques, including lipid-mixing and cor e-mixing assays using pyrene-labeled vesicles. The effect of peptide e longation toward the N-terminal end of the entire beta-amyloid peptide was also investigated. Peptides corresponding to residues 22-42 and 1 2-42 were tested using the same techniques. Both the 29-40 and 29-42 b eta-amyloid peptides were able to induce fusion of unilamellar lipid v esicles and calcein leakage, and the amyloid 29-42 peptide was the mos t potent fusogenic peptide. Neither the two mutants or the 13-28 beta- amyloid peptide had any fusogenic activity. Circular dichroism measure ments showed an increase of the alpha-helical content of the two C-ter minal peptides at increasing concentrations of trifluoroethanol, which was accompanied by an increase of the fusogenic potential of the pept ides. Our data suggest that the alpha-helical content and the angle of insertion of the peptide into a lipid bilayer are critical for the fu sogenic activity of the C-terminal domain of the amyloid peptide. The differences observed between the fusogenic capacity of the amyloid 29- 40 and 29-42 peptides might result from differences in the degree of p enetration of the peptides into the membrane and the resulting membran e destabilization. The longer peptides, residues 22-42 and 12-42, had decreased, but significant, fusogenic properties associated with pertu rbation of the membrane permeability. These data suggest that the fuso genic properties of the C-terminal domain of the beta-amyloid peptide might contribute to the cytotoxicity of the peptide by destabilizing t he cell membrane.