Site-specific effects of peptide lipidation on β-amyloid aggregation and cytotoxicity

Abstract

β-Amyloid (Aβ) 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 Nα-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 Nα-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 ≈ Nα-OA-Aβ ≫ K16-OA-Aβ ≫ K28-OA-Aβ). By CD spectroscopy, K16-OA-Aβ and K28-OA-Aβ had increased β-sheet propensity compared with Aβ-(1-40) or Nα-OA-Aβ. K16-OA-Aβ and K28-OA-Aβ were more amphiphilic than Aβ-(1-40) or Nα-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 Nα-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. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.