Structural and mechanistic insights into amyloid‐β and α‐synuclein fibril formation and polyphenol inhibitor efficacy in phospholipid bilayers

Abstract

Under certain cellular conditions, functional proteins undergo misfolding, leading to a transition into oligomers which precede the formation of amyloid fibrils. Misfolding proteins are associated with neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. While the importance of lipid membranes in misfolding and disease aetiology is broadly accepted, the influence of lipid membranes during therapeutic design has been largely overlooked. This study utilized a biophysical approach to provide mechanistic insights into the effects of two lipid membrane systems (anionic and zwitterionic) on the inhibition of amyloid-b 40 and a-synuclein amyloid formation at the monomer, oligomer and fibril level. Large unilamellar vesicles (LUVs) were shown to increase fibrillization and largely decrease the effectiveness of two well-known polyphenol fibril inhibitors, (-)epigallocatechin gallate (EGCG) and resveratrol; however, use of immunoblotting and ion mobility mass spectrometry revealed this occurs through varying mechanisms. Oligomeric populations in particular were differentially affected by LUVs in the presence of resveratrol, an elongation phase inhibitor, compared to EGCG, a nucleation targeted inhibitor. Ion mobility mass spectrometry showed EGCG interacts with or induces more compact forms of monomeric protein typical of off-pathway structures; however, binding is reduced in the presence of LUVs, likely due to partitioning in the membrane environment. Competing effects of the lipids and inhibitor, along with reduced inhibitor binding in the presence of LUVs, provide a mechanistic understanding of decreased inhibitor efficacy in a lipid environment. Together, this study highlights that amyloid inhibitor design may be misguided if effects of lipid membrane composition and architecture are not considered during development.

Lipid Oxidation Controls Peptide Self-Assembly near Membranes

“…The acceleration of Aβ 40 aggregation in the presence of membrane surfaces is in agreement with previous studies 89 while an enhanced β-sheet formation of the related Aβ 42 peptide has been observed on oxidatively damaged surfaces, in particular. 69 The inhibition of U3.5 aggregation in the presence of POPG containing liposomes (POPG, POPC-POPG, 4:1) is also in agreement with our prior work when DMPG (1,2-dimyristoyl- sn -glycero-3-phospho-(1’-rac-glycerol)) lipid systems were studied.…”

Lipids and EGCG Affect α-Synuclein Association and Disruption of Nanodiscs

“…Native MS revealed the stoichiometry of binding of α-syn to nanodiscs as well as any smaller complexes formed. We used relatively low concentrations compared to prior studies, so we do not expect or observe significant fibril formation on the time scale of these experiments. ,, Higher-order oligomeric species were not detected, so we focus mainly on interactions between monomeric α-syn and the nanodisc bilayer.…”

“…Protein misfolding and aggregation are linked with a range of neurodegenerative disorders. − However, the molecular basis of protein misfolding and toxicity in these diseases remains elusive, and there are no suitable therapeutic approaches to prevention. Recently, lipid membranes have been implicated in protein misfolding and disease etiology, but our current understanding of the interplay among misfolded oligomers, fibrils, and lipids is unclear. − The lipid membrane composition, including headgroup and tail, can play an important role in misfolding protein aggregation kinetics and affect the morphologies of oligomers and fibrils. − Because neuronal lipids change with age, the lipid environment may be an important driver of disease risk with increasing age …”

Polyphenol characterisation and diverse bioactivities of native Australian lilly pilly (Syzygium paniculatum) extract

“…2). 32,33 The three plant extracts tested significantly reduced both the rate and degree of αS fibril formation at a 1 : 1 ratio, however, purple sweet potato and blackberry extracts showed a concentration dependent decrease in fibril inhibition, with greatly reduced inhibition at a 10 : 1 ratio. In contrast, the lilly pilly extract exerted potent inhibitory activity across the three ratios tested and had comparable activity to EGCG (Fig.…”