A Capped Peptide of the Aggregation Prone NAC 71–82 Amino Acid Stretch of α-Synuclein Folds into Soluble β-Sheet Oligomers at Low and Elevated Peptide Concentrations

Abstract

Although Lewy bodies and Lewy neurites are hallmarks of Parkinson’s disease (PD) and dementia with Lewy bodies (DLB), misfolded α-synuclein oligomers are nowadays believed to be key for the development of these diseases. Attempts to target soluble misfolded species of the full-length protein have been limited so far, probably due to the fast aggregation kinetics and burial of aggregation prone segments in final cross-β-sheet fibrils. A previous characterisation study of fibrils prepared from a capped peptide of the non-amyloid β-component (NAC) 71–82 amino acid stretch of α-synuclein demonstrated an increased aggregation propensity resulting in a cross-β-structure that is also found in prion proteins. From this, it was suggested that capped NAC 71–82 peptide oligomers would provide interesting motifs with a capacity to regulate disease development. Here, we demonstrated, from a series of circular dichroism spectroscopic measurements and molecular dynamics simulations, the molecular-environment-sensitive behaviour of the capped NAC 71–82 peptide in a solution phase and the formation of β-sheet oligomeric structures in the supernatant of a fibrillisation mixture. These results highlighted the use of the capped NAC 71–82 peptide as a motif in the preparation of oligomeric β-sheet structures that potentially could be used in therapeutic strategies in the fight against progressive neurodegenerative disorders, such as PD and DLB.

Influence of Protonation on the Norepinephrine Inhibiting α-Synuclein 71–82 Oligomerization

“…The pathogenesis of PD is closely associated with the massive presence of Lewy vesicles and Lewy axons in the cytoplasm of neurons, − whose main component is α-synuclein (αS), a 14 kDa protein comprising 140 residues. , The mature αS fibrils are insoluble and have a common cross-β structure like other amyloid fibrils with hydrogen-bonded β-sheet structures aligned perpendicular to the fibril axis. , It consists of an amphipathic N-terminal region (residues 1–60), a hydrophobic nonamyloid component (NAC, residues 61–95) region, and a negatively charged C-terminal region (residues 96–140), − which are responsible for different molecular and biological properties . The NAC region is the most aggregation-prone, whose hydrophobic segment of residues 71–82 (αS 71–82 ) is essential for αS oligomerization, and the deletion of this segment abolishes the ability of αS to self-assemble. , αS 71–82 is also capable of forming fibrils on its own and shares similar β-sheet-rich, amyloid-like morphologies to full-length αS fibrils. − Yet, resolving the high-resolution crystal structure of fibrils is still a very challenging task.…”

A Perspective on Interdicting in Protein Misfolding for Therapeutic Drug Design: Modulating the Formation of Nonlocal Contacts in α-Synuclein as a Strategy against Parkinson’s Disease

“…115 Finally, experiments have also shown that a capped peptide including the segment 71 VTGVTAVAQKTV 82 tends to form β-sheet rich oligomers under prefibrillar conditions. 83 These results, combined with the lack of pathogenic aggregation of truncated α-synuclein, suggest a hypothesis concerning the relationship between nonlocal contact formation and the α-synuclein aggregation and pathogenicity mechanism. This hypothesis would imply that aggregation of α-synuclein is favored by an altered equilibrium between the best nonlocal contact defined by segments 37 VLYCG 42 and 91 ATGFV 95 , and the second best, established between segments 1 MDVFM 5 and 70 VVTGV 74 , that increases the relative population of the latter.…”

“…Also, small hydrophobic self-peptides can interact among themselves and produce amyloid-like aggregates. 83 Due to the motivational reasons discussed earlier, combined with the high human toll of protein-misfolding related diseases, make it important to investigate the feasibility of employing folding interdiction for therapeutic drug design for proteinopathies. In the next sections we will explain that α-synuclein is, in principle, a suitable system to study the matter, and a possible interdiction approach for it will be introduced.…”

Peptide–Peptide Co-Assembly: A Design Strategy for Functional Detection of C-peptide, A Biomarker of Diabetic Neuropathy

“…Complementary to ATR-FTIR spectroscopy, CD spectroscopy is able to provide information on changes in the secondary structures after C-peptide–com-peptide co-assembly [ 31 , 32 , 36 ]. Figure 7 illustrates the CD spectra of C-peptide, Trp-D, Lys-D, and Lys-L.…”

“…Complementary to ATR-FTIR spectroscopy, CD spectroscopy is able to provide information on changes in the secondary structures after C-peptide-com-peptide co-assembly. [31,32,36] Figure 7 illustrates the CD spectra of C-peptide, Trp-D, Lys-D, and Lys-L. The CD spectra of C-peptide suggest that it largely adopt a polyproline II helical structure, as the negative peaks at 198 nm and 226 nm suggest.…”