Summary: The conformational change of the 39–43 residues of the amyloid β-peptide (Aβ) toward a β-sheet enriched state promotes self-aggregation of the peptide molecules and constitutes the major peptide component of the amyloid plaques in Alzheimer patients. The crucial question behind the self-aggregation of Aβ is related to the different pathways the peptide may take after cleavage from the amyloid precursor proteins at cellular membranes. This work is aiming at determining the conformation of the Aβ (1–40) adsorbed on hydrophobic Teflon and hydrophilic silica particles, as model sorbent surfaces mimicking the apolar transmembrane environment and the polar, charged membrane surface, respectively. The mechanism by which the Aβ interacts with solid surfaces strongly depends on the hydrophobic/hydrophilic character of the particles. Hydrophobic and electrostatic interactions contribute differently in each case, causing a completely different conformational change of the adsorbed molecules on the two surfaces. When hydrophobic interactions between the peptide and the sorbent prevail, the adsorbed Aβ (1–40) mainly adopts an α-helix conformation due to H-bonding in the apolar part of the peptide that is oriented towards the surface. On the other hand, when the peptide adsorbs by electrostatic interactions β-sheet formation is promoted due to intermolecular association between the apolar parts of the adsorbed peptide. Irrespective of the characteristics of the solid sorbent, crowding the surface results in intermolecular association between adsorbed molecules leading to a strong aggregation tendency of the Aβ (1–40).
CD spectra of Aβ (1–40) at pH 7: A) in solution ([Aβ] = 0.2 mg · ml−1) freshly prepared (line) and after overnight incubation (symbols); B) on Teflon (Γ = 0.5 mg · m−2).