Interaction of Alzheimer β-Amyloid Peptide(1−40) with Lipid Membranes

Abstract

The beta-amyloid peptide beta AP(1-40), a 40-amino acid residues peptide, is one of the major components of Alzheimer's amyloid deposits. beta AP(1-40) exhibits only a limited solubility in aqueous solution and undergoes a concentration-dependent, cooperative random coil reversible beta-structure transition for Cpep > 10 microM [Terzi, E., Hölzemann, G., and Seelig, J. (1995) J. Mol. Biol. 252, 633-642]. In the presence of acidic lipid, the equilibrium is shifted further toward beta-structured aggregates. We have now characterized the lipid-peptide interaction using circular dichroism (CD) spectroscopy, lipid monolayers, and deuterium and phosphorus-31 solid-state nuclear magnetic resonance (NMR). CD spectroscopy revealed a distinct interaction between beta AP(1-40) and negatively charged unilamellar vesicles. In addition to the random coil reversible beta-structured aggregate equilibrium at low lipid-to-peptide (L/P) ratios, a beta-structure -->alpha-helix transition was observed at L/P > 55. beta AP(1-40) was found to insert into acidic monolayers provided the lateral pressure was low (20 mN/m). The extent of incorporation increased distinctly with the content of acidic lipid in the monolayer. However, at a lipid packing density equivalent to that of a bilayer (lateral pressure> or = 32 mN/m), no insertion of beta AP(1-40) was observed. The lipid molecular structure in the presence of beta AP(1-40) was studied with NMR. Phosphatidylcholine (PC) was selectively deuterated at the choline headgroup and at the cis-double bond of the oleic acyl chain and mixed with phosphatidylglycerol (PG). Phosphorus-31 NMR showed that the lipid phase retained the bilayer structure at all lipid-to-protein ratios. Deuterium NMR revealed no change in the headgroup conformation of the choline moiety or in the flexibility and ordering of the hydrocarbon chains upon the addition of beta AP-(1-40). It can be concluded that beta AP(1-40) binds electrostatically to the outer envelope of the polar headgroup region without penetrating between the polar groups. The data suggest a new mechanism of helix formation induced by the proper alignment of five positive charges of beta AP(1-40) on the negatively charged membrane template.

Cholesterol Is an Important Factor Affecting the Membrane Insertion of β-Amyloid Peptide (Aβ1–40), Which May Potentially Inhibit the Fibril Formation

“…Several laboratories have reported their CD work on A␤. Different experimental conditions may induce different A␤ conformations: (i) the ␣-helix in trifluoroethanol, SDS micelles, or induced by ganglioside-containing vesicles (34, 35, 46 -49), and also in our experiments when we used ethanol-water system to simulate the membrane condition, and the CD results indicate that the ␣-helix increases along with an increase of the ethanol content (data not shown), which coincides with the previous reports very well; (ii) essentially random-coil structures with ␤-turns in aqueous solution at low peptide concentrations; and (iii) ␤-structured aggregates in solution or in contact with lipid membranes (2,34). So far to our knowledge, systems containing cholesterol, which assuredly is the common component of membranes, are not employed yet in these published papers.…”

“…By comparing the difference in the spectra among them in Fig. 4, we can find that the inaccessible cleavage sites are Gly 33 -Leu 34 and Gly 37 -Gly 38 . Both sites are located in the C-terminal region of A␤.…”

Single-cell mechanics provides a sensitive and quantitative means for probing amyloid-β peptide and neuronal cell interactions

“…The protein molecules therefore are likely to intercalate into the cellular membrane. This conclusion is consistent with prior knowledge that the Aβ42 oligomer binds with high affinity with various membrane components, such as the outer envelope of polar headgroups, ganglioside clusters in raftlike structures, insulin receptors, α 5 β 1 integrin, and α7nAChR protein, to name a few (14,18,33).…”

“…To quantify contributions further, we separate (i) the binding of Aβ oligomers to various membrane components (such as the outer envelope of polar headgroups, ganglioside clusters in rafts, insulin receptors, α 5 β 1 integrin, and α7nAChR protein, to name a few) (14,18,33), and (ii) the treatment that alters membrane permeability by changing ion channels or making new pores, resulting in increased intracellular ion concentration. The former reduces fluidity and increases spring constant; the latter leads to greater osmotic pressure, which manifests into stiffer forcedeformation profiles.…”

Amyloid-β Protofibrils Differ from Amyloid-β Aggregates Induced in Dilute Hexafluoroisopropanol in Stability and Morphology

“…Both A␤ Protofibrils and HFIP-induced A␤ Aggregates Are Rich in ␤-Structure-Previous analyses of CD spectra for 39 -42-residue A␤ peptides prior to aggregation have concluded that the conformations are largely random coil in aqueous buffers (37,54) and predominantly ␣-helical in acidic (55) and neutral (56) pH solutions that contain Ն20% HFIP. Our spectra in Fig.…”