[Protein Structure and Folding] Site-specific Effects of Peptide Lipidation on -Amyloid Aggregation and Cytotoxicity

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[Protein Structure and Folding] Site-specific Effects of Peptide Lipidation on -Amyloid Aggregation and Cytotoxicity

β-Amyloid (A&beta aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of Aβ 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 Aβ at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-Aβ, K28-OA-Aβ, and N-OA-Aβ. Octanoylation of these sites on Aβ-(1–40) had strikingly different effects on fibril formation. K16-OA-Aβ and K28-OA-Aβ, but not N-OA-Aβ, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-Aβ peptides to cross-seed solutions of Aβ was the inverse of their ability to form fibrils on their own (i.e. Aβ N-OA-Aβ >> K16-OA-Aβ >> K28-OA-A&beta. By CD spectroscopy, K16-OA-Aβ and K28-OA-Aβ had increased β-sheet propensity compared with Aβ-(1–40) or N-OA-Aβ. K16-OA-Aβ and K28-OA-Aβ were more amphiphilic than Aβ-(1–40) or N-OA-Aβ, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-Aβ and K28-OA-Aβ are much more cytotoxic to N2A cells than Aβ-(1–40) or N-OA-Aβ. The greater cytotoxicity of K16-OA-Aβ and K28-OA-Aβ may reflect their greater amphiphilicity. We conclude that lipidation can make Aβ more prone to aggregation and more cytotoxic, but these effects are highly site-specific.