Monomeric Amyloid Beta Peptide in Hexafluoroisopropanol Detected by Small Angle Neutron Scattering

Abstract

Small proteins like amyloid beta (Aβ) monomers are related to neurodegenerative disorders by aggregation to insoluble fibrils. Small angle neutron scattering (SANS) is a nondestructive method to observe the aggregation process in solution. We show that SANS is able to resolve monomers of small molecular weight like Aβ for aggregation studies. We examine Aβ monomers after prolonged storing in d-hexafluoroisopropanol (dHFIP) by using SANS and dynamic light scattering (DLS). We determined the radius of gyration from SANS as 1.0±0.1 nm for Aβ1–40 and 1.6±0.1 nm for Aβ1–42 in agreement with 3D NMR structures in similar solvents suggesting a solvent surface layer with 5% increased density. After initial dissolution in dHFIP Aβ aggregates sediment with a major component of pure monomers showing a hydrodynamic radius of 1.8±0.3 nm for Aβ1–40 and 3.2±0.4 nm for Aβ1–42 including a surface layer of dHFIP solvent molecules.

SANS study of Amyloidβ1−40: Unfolded monomers in DMSO, multidimensional aggregates in water medium

“…The Structure factor S(Q) equals 1 for low concentrations as in our case and the Form factor F(Q) depends on the shape and size of the scattering objects but not on the concentration. The data analysis was carried out by using a geometry independent Form factor known as the Becauge model [15,26]:…”

“…Instead, Zhang-Haagen et al showed that SANS is able to resolve monomers of small molecular weight such as Aβ in deuterated HFIP, of a radius of gyration of 1.0 ± 0.1 nm (in agreement with 3D NMR). [15] To evaluate the possibilities and limitations of SANS technique to observe size and conformational characteristics of Aβ, we evaluated Aβ 1−40 , the most common Aβ peptide, in disparate solvents. Since water (H 2 O or D 2 O buffers) can induce fast aggregation of monomer while DMSO can disaggregate Aβ oligomers/fibrils, we examined Aβ 1−40 monomeric solution in DMSO, and Aβ 1−40 oligomer and protofibril preparations in biological relevant environment (D 2 O buffers).…”

Fullerenemalonates inhibit amyloid beta aggregation, in vitro and in silico evaluation

“…The Ab 42 monomer (1 mg) was resuspended in 1 ml of cold 1,1,1,3,3,3-hexauoro-2-propanol (HFIP), and it was kept in the dark for 30 min at 4 C to solubilize the peptide in the monomeric stage. 44,45 The solution was aliquoted (25 ml) and dried under vacuum in a rotary evaporator for 1 h at room temperature; the resultant transparent lm was stored at À80 C for further experiments. The amyloid brils were formed as previously described; 46 briey, the solubilized Ab 42 was dissolved in polymerization buffer containing PBS 1Â (nal concentration of 10 mM PO 4 3À , 137 mM NaCl, and 2.7 mM KCl) and 1% DMSO and incubated at 37 C at different time points.…”

The impact of water on the ambivalent behavior and paradoxical phenomenon of the amyloid-β fibril protein

“…Although this molecule is missing the Ile and Ala amino acid (41)(42) residues: the C-terminal part of the Aβ 42 fibril protein, does not make any essential difference in the structure and or in the conformation. [The hydropathy indices are: Ile = 4.5; Ala = 1.8 (23). ]…”

“…The third team also studied this molecule by cryo-electron microscopy (22). On the other hand, a hairpin-like structure of the full-length Aβ 42 monomer was determined by NMR (18) and by small angle neutron scattering (23) in the presence of organic co-solvents (e.g. hexafluoroisopropanol), as shown in Figure 1.…”