Stabilization of a Membrane-Associated Amyloid-β Oligomer for Its Validation in Alzheimer's Disease

Abstract

We have recently reported on the preparation of a membrane-associated β-barrel Pore-Forming Aβ42 Oligomer (βPFOAβ42). It corresponds to a stable and homogeneous Aβ42 oligomer that inserts into lipid bilayers as a well-defined pore and adopts a specific structure with characteristics of a β-barrel arrangement. As a follow-up of this work, we aim to establish βPFOAβ42's relevance in Alzheimer's disease (AD). However, βPFOAβ42 is formed under dodecyl phosphocholine (DPC) micelle conditions—intended to mimic the hydrophobic environment of membranes—which are dynamic. Consequently, dilution of the βPFOAβ42/DPC complex in a detergent-free buffer leads to dispersion of the DPC molecules from the oligomer surface, leaving the oligomer without the hydrophobic micelle belt that stabilizes it. Since dilution is required for any biological test, transfer of βPFOAβ42 from DPC micelles into another hydrophobic biomimetic membrane environment, that remains associated with βPFOAβ42 even under high dilution conditions, is a requisite for the validation of βPFOAβ42 in AD. Here we describe conditions for exchanging DPC micelles with amphipols (APols), which are amphipathic polymers designed to stabilize membrane proteins in aqueous solutions. APols bind in an irreversible but non-covalent manner to the hydrophobic surface of membrane proteins preserving their structure even under extreme dilution conditions. We tested three types of APols with distinct physical-chemical properties and found that the βPFOAβ42/DPC complex can only be trapped in non-ionic APols (NAPols). The characterization of the resulting βPFOAβ42/NAPol complex by biochemical tools and structural biology techniques allowed us to establish that the oligomer structure is maintained even under high dilution. Based on these findings, this work constitutes a first step towards the in vivo validation of βPFOAβ42 in AD.

Clear distinction between CAC and CMC revealed by high-resolution NMR diffusometry for a series of bis-imidazolium gemini surfactants in aqueous solutions

“…57 CAC values are also meaningful in some specic applications like in case of amphiphilic molecules for membrane protein stabilization at high dilutions. 58 Also, it was proven that above CAC the viscosity of surfactant solution decreases signicantly, 53 which could probably inhibit the unfavourable process of protein aggregation called amyloidogenesis, which leads to neurodegenerative disorders. 59 Additionally, determination of CAC and CMC values for gemini surfactants is essential for optimization of their usage as delivery systems for nucleic acid in gene therapy.…”

Theory of concentric β-barrel structures: models of amyloid beta 42 oligomers, annular protofibrils, and transmembrane channels

“…They find that these assemblies form highly stable ion channels with only one principal conductance (ignoring flickering currents that occurs in some, but not all, of their experiments). They have also developed a method to test the toxicity of these assemblies in vitro 11 . But Aβ42 likely forms a variety of discrete channels.…”

NANOTHERAPY TO DELAY COGNITIVE IMPAIRMENT: USING COLLOIDAL NANOCARRIERS TO BLOCK AMYLOID-β-INDUCED DAMAGE IN BRAIN CELL MEMBRANES

“…γ-Secretase cleavage occurs in the transmembrane domain, of the C-terminal fragment left by β-secretase cleavage, and results in the release of Aβ peptides of various lengths [126]. The longer, neurotoxic, Aβ(1-42) peptide is highly aggregation prone and represents the major Aβ species deposited in the brain [126][127][128][129]. Cholesterol promotes Aβ(1-42) aggregation by enhancing its primary nucleation rate by up to 20-fold [129].)…”