Peptide backbone modifications of amyloid β (1–40) impact fibrillation behavior and neuronal toxicity

Abstract

Fibril formation of amyloid β (Aβ) peptides is one of the key molecular events connected to Alzheimer’s disease. The pathway of formation and mechanism of action of Aβ aggregates in biological systems is still object of very active research. To this end, systematic modifications of the Phe19–Leu34 hydrophobic contact, which has been reported in almost all structural studies of Aβ40 fibrils, helps understanding Aβ folding pathways and the underlying free energy landscape of the amyloid formation process. In our approach, a series of Aβ40 peptide variants with two types of backbone modifications, namely incorporation of (i) a methylene or an ethylene spacer group and (ii) a N-methylation at the amide functional group, of the amino acids at positions 19 or 34 was applied. These mutations are expected to challenge the inter-β-strand side chain contacts as well as intermolecular backbone β-sheet hydrogen bridges. Using a multitude of biophysical methods, it is shown that these backbone modifications lead, in most of the cases, to alterations in the fibril formation kinetics, a higher local structural heterogeneity, and a somewhat modified fibril morphology without generally impairing the fibril formation capacity of the peptides. The toxicological profile found for the variants depend on the type and extent of the modification.

Does Inflammation Play a Major Role in the Pathogenesis of Alzheimer's Disease?

“…In 1991, three independent research teams proposed the involvement of Aβ accumulation in the pathogenesis of AD. This hypothesis holds that Aβ deposition is the earliest event in AD progression (Schwarze et al, 2021). Aβ is generated from amyloid precursor protein (APP) by abnormal proteolytic cleavage by β-and γ-secretases (Vadukul et al, 2021).…”

How Single Site Mutations Can Help Understanding Structure Formation of Amyloid β1−40

“…[ 53,55,82 ] Experiments that measure motionally averaged anisotropic interactions can assess the flexibility of amino acid side chains. [ 83–85 ] On the other hand, solution NMR spectroscopy can help to investigate transient/oligomeric species soluble in aqueous media before reaching the insoluble fibril state, [ 86 ] and H/D exchange has been exploited also for structural calculations. [ 87 ]…”

“…Therefore, two types of backbone modifications were introduced, namely, incorporation of either a methylene ( X+1 ) or an ethylene ( X+2 ) spacer group or, second, an N ‐methylation at the amide functional group ( N ‐Me‐X ). [ 84 ] The backbone extension is supposed to increase the degrees of freedom in the peptide backbone in order to perturb the ordered in‐register hydrophobic zipper structure motif. F19+1 as well as F19+2 showed shorter lag time regarding their fibrillation behavior, but same fibrillation time compared to WT.…”

Identifying interaction interface betweenPseudomonasmajor biofilm forming functional amyloid FapC and disordered chaperone FapA during fibrillation deceleration

“…34 Solution NMR has been utilized successfully to characterize NMR-visible soluble monomeric species as well as the NMR-invisible high molecular-weight oligomeric/protofilament and sparsely populated oligomeric species of several different amyloid fibrils from both pathologic and functional amyloids. 32,[35][36][37][38][39][40][41][42][43][44] These methods are also summarized in an excellent recent review. 32 A few very important points to note here concerning fibril formation are the sample concentration, temperature, and the freshness of the prepared samples to be in an absolute monomeric state in the NMR experiments.…”

“…34 Solution NMR has been utilized successfully to characterize NMR-visible soluble monomeric species as well as the NMR-invisible high molecular-weight oligomeric/protofilament and sparsely populated oligomeric species of several different amyloid fibrils from both pathologic and functional amyloids. 32, 35–39, 40–44 These methods are also summarized in an excellent recent review. 32…”