THE 118-135 PEPTIDE LOT THE HUMAN PRION PROTEIN FORMS AMYLOID FIBRILSAND INDUCES LIPOSOME FUSION

The prion protein (PrPC) is a glycoprotein of unknown function normall y found at the surface of neurons and of glial cells. It is involved i n diseases such as bovine spongiform encephalopathy, and Creutzfeldt-J akob disease in the human, where PrPC is converted into an altered for m (termed PrPSc). PrPSc is highly resistant towards proteolytic degrad ation and accumulates in the central nervous system of affected indivi duals. By analogy with the pathological events occuring during the dev elopment of Alzheimer's disease, controverses still exist regarding th e relationship between amyloidogenesis, prion aggregation and neuronal loss. To unravel the mechanism of PrP neurotoxicity and understand th e interaction of PrP with cellular membranes, a series of natural and variant peptides spanning residues 118 to 135 of PrP was synthesized. The potential of these peptides to induce fusion of unilamellar lipid vesicles was investigated. According to computer modeling calculations , the 120 to 133 domain of PrP is predicted to be a tilted lipid-assoc iating peptide, and to insert in a oblique way into a lipid bilayer th rough its N-terminal end. In addition to amyloidogenic properties exhi bited ill vitro by these peptides, peptide-induced vesicle fusion was demonstrated by several techniques, including lipid-and core-mixing as says. Elongation of the 120 to 133 peptide towards the N- and C-termin al ends of the PrP sequence showed that the 118 to 135 PrP peptide has maximal fusogenic properties, while the variant peptides had no effec t. Due to their high hydrophobicity, all peptides tested were able to interact with liposomes to induce leakage of encapsulated calcein. We demonstrate also that the propensity of the peptides to fold as an alp ha-helix increases their fusogenic activity, thus accounting for the m aximal fusogenic activity of the most stable helix at residues 118 to 135. These data suggest that, by analogy with the C-terminal domain of the beta-amyloid peptide, the fusogenic properties exhibited by the p rion peptides might contribute to the neurotoxicity of these peptides by destabilizing cellular membranes. (C) 1997 Academic Press Limited.