Amyloid ß-peptide (Aß) aggregates are one of the key neuropathological characteristics of Alzheimer's disease. Aß belongs to a group of proteins that aggregate and form ß-sheets, and some of these proteins bind cholesterol and other lipids.

The effects of soluble and aggregated amyloid ␤-peptide (A␤) on cortical synaptic plasma membrane (SPM) structure were examined using small angle x-ray diffraction and fluorescence spectroscopy approaches. Electron density profiles generated from the x-ray diffraction data demonstrated that soluble and aggregated A␤ 1-40 peptides associated with distinct regions of the SPM. The width of the SPM samples, including surface hydration, was 84 Å at 10°C. Following addition of soluble A␤ 1-40 , there was a broad increase in electron density in the SPM hydrocarbon core ؎0 -15 Å from the membrane center, and a reduction in hydrocarbon core width by 6 Å. By contrast, aggregated A␤ 1-40 contributed electron density to the phospholipid headgroup/hydrated surface of the SPM ؎24 -37 Å from the membrane center, concomitant with an increase in molecular volume in the hydrocarbon core. The SPM interactions observed for A␤ 1-40 were reproduced in a brain lipid membrane system. In contrast to A␤ 1-40 , aggregated A␤ 1-42 intercalated into the lipid bilayer hydrocarbon core ؎0 -12 Å from the membrane center. Fluorescence experiments showed that both soluble and aggregated A␤ 1-40 significantly increased SPM bulk and protein annular fluidity. Physico-chemical interactions of A␤ with the neuronal membrane may contribute to mechanisms of neurotoxicity, independent of specific receptor binding. Alzheimer's disease (AD)1 is a progressive neurodegenerative disorder characterized by the accumulation of neuritic plaques composed of amyloid ␤-peptide (A␤) variants, extracellular matrix components, and apolipoproteins (1, 2). A␤ is an amphipathic, 39 -42-residue peptide that is derived by proteolytic cleavage of the transmembrane glycoprotein, the amyloid precursor protein; the A␤ domain is composed of 28 extracellular and 12-14 transmembrane amino acid residues of amyloid precursor protein (3). An increase in the production and abnormal accumulation of A␤ in the brain has been implicated in the etiology of AD. Several studies have shown that A␤ analogs can directly disrupt neuronal function, contributing to cell death associated with the development of AD (4 -8).It has been postulated that the biological activity of A␤ is related to its ability to form insoluble aggregates in solution (9 -11), although the cellular mechanism of action is not well understood. A recent study from Cotman and co-workers (12) showed that A␤ neurotoxicity is independent of stereoisomerspecific ligand-receptor interaction because both all-D-and all-L-stereoisomers of A␤ [25][26][27][28][29][30][31][32][33][34][35] and A␤ 1-40 had similar neurotoxic activity. This finding suggests that A␤ modulates membrane function by a nonreceptor-mediated mechanism, potentially as a result of altering the physico-chemical properties of membrane constituents, including lipids and proteins (13-16). Indeed, previous membrane equilibrium binding experiments have demonstrated that the A␤ 25-35 fragment is highly lipophilic (K P Ͼ 10 2 ); the peptide intercalates deep into the membra...

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Molecular mechanisms of ethanol interaction with proteins are not well-understood. In the present study, direct interaction of ethanol with hydrophobic binding sites on fatty acid free bovine serum albumin (BSA) was determined using the fluorescent probe 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS), cis-parinaric acid, and 13C NMR. The affinity of ethanol for BSA (Kd) was (5.21 +/- 0.31) x 10(-2) mol. Ethanol (25-200 mmol) competitively inhibited 1,8-ANS binding to BSA in a concentration-dependent manner with a Ki (concentration of ethanol that decreased 1,8-ANS binding by 50%) of 658 mmol. Preincubation of BSA with ethanol significantly decreased cis-parinaric acid binding to BSA, indicating interaction of ethanol with hydrophobic fatty acid-binding site(s) on BSA. Furthermore, ethanol was found to act on three of the five fatty acid-binding sites on BSA. These data indicated selectivity in the interaction of ethanol with hydrophobic sites on BSA. 13C NMR multiplet relaxation was used to characterize the interaction of ethanol with binding sites on BSA. Detailed analysis of [13C]ethanol relaxation data obtained in the presence of increasing BSA concentrations (25-200 mg/mL) led to the conclusion that the ethanol methyl group, as opposed to its hydroxyl group, binds in a hydrophobic pocket(s) on the protein. Ethanol-induced changes in activity of certain proteins may result from direct binding of ethanol to specific hydrophobic binding sites and/or displacement of endogenous ligands from those sites.