Alzheimer .beta.-Amyloid Peptide 25-35: Electrostatic Interactions with Phospholipid Membranes

Abstract

The role of lipids in the aggregation of three Alzheimer model peptides was investigated with circular dichroism spectroscopy and high-sensitivity titration calorimetry under conditions of low ionic strength. In solution, the peptides beta AP(25-35)OH and beta AP(25-35Nle)NH2 exhibit a reversible random-coil<-->beta-sheet (or beta-structured aggregate) transition. Addition of lipid vesicles containing negatively charged lipids shifts the random-coil<-->beta-sheet equilibrium almost completely toward beta-sheet structure, which can be explained by the specific conditions created at the membrane surface: the cationic peptides are attracted to the negatively charged membrane, and the increase in peptide concentration together with the partial alignment of the peptide molecules then facilitates beta-sheet formation. The third peptide, beta AP-(25-35)NH2, also binds to the lipid membrane but was found to adopt an essentially random-coil structure, both with and without lipids. A quantitative characterization of the binding equilibrium was possible with high-sensitivity titration calorimetry. All three peptides exhibited exothermic binding enthalpies which varied between delta H approximately -2 kcal/mol for beta AP(25-35)OH and -8 kcal/mol for beta AP(25-35)NH2. The apparent binding constants, calculated with bulk concentrations, were large and varied between 500 and 5 x 10(4) M-1, depending on the experimental conditions. However, after correction for electrostatic charge effects using the Gouy-Chapman theory, the intrinsic binding constants were found to be constant and much smaller with K approximately 2-10 M-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the Interactions of Alzheimer β‐Amyloid Peptides with Phospholipid Membranes

“…Lipid aggregation was followed by means of light scattering at 400 nm, at pH 6.0 (A and C) and pH 7.0 (B and D). Vesicles were composed of PtdGro (0) (Terzi et al, 1994). These results are consistent with our data, although the dye-release assay and lipid-aggregation studies might imply a lower affinity of AAPP-(25-35)-peptide for lipids.…”

Effect of Cholesterol Reduction on Receptor Signaling in Neurons

“…Amyloid ␤, one of the pathogenic components of Alzheimer disease, interacts with membrane lipids in the initial stage of the neurodegenerative change (33,34). To determine whether cholesterol depletion affected apoptosis, we assessed annexin V-allophycocyanin binding (35) and 7-AAD uptake following exposure of the cells to amyloid ␤ using flow cytometry.…”

Microglial Phagocytosis of Fibrillar β-Amyloid through a β1Integrin-Dependent Mechanism

“…1 A, B). We have documented previously that microglia respond to fibrillar forms (but not nonfibrillar forms) of A␤1-40, A␤1-42, and A␤25-35 (Terzi et al, 1994) by stimulation of intracellular signaling cascades (McDonald et al, 1997;Combs et al, 1999;Bamberger et al, 2003). When the experiments were conducted at 4°C, stimulation of phagocytosis was not detected (data not shown).…”