Site-specific Effects of Peptide Lipidation on β-Amyloid Aggregation and Cytotoxicity

Abstract

-Amyloid (A) aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of A by 4-hydroxynonenal (4-HNE) initially increases the hydrophobicity of these peptides and subsequently leads to additional reactions, such as peptide cross-linking. To model these initial events, without confounding effects of subsequent reactions, we modified A at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-A, K28-OA-A, and N-OA-A. Octanoylation of these sites on A-(1-40) had strikingly different effects on fibril formation. K16-OA-A and K28-OA-A, but not N-OA-A, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-A peptides to cross-seed solutions of A was the inverse of their ability to form fibrils on their own (i.e. A N-OA-A K16-OA-A K28-OA-A). By CD spectroscopy, K16-OA-A and K28-OA-A had increased -sheet propensity compared with A-(1-40) or N-OA-A. K16-OA-A and K28-OA-A were more amphiphilic than A-(1-40) or N-OA-A, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-A and K28-OA-A are much more cytotoxic to N2A cells than A-(1-40) or N-OA-A. The greater cytotoxicity of K16-OA-A and K28-OA-A may reflect their greater amphiphilicity. We conclude that lipidation can make A more prone to aggregation and more cytotoxic, but these effects are highly site-specific.