α-Helical peptidic scaffolds to target α-synuclein pathogenic species with high affinity and selectivity

Abstract

α-Synuclein aggregation is a key driver of neurodegeneration in Parkinsons disease and related syndromes. Accordingly, obtaining a molecule that targets α-synuclein pathogenic assemblies with high affinity and selectivity is a long-pursued objective. Here, we have exploited the biophysical properties of toxic oligomers and amyloid fibrils to identify a family of α-helical peptides that bind selectively to these α-synuclein species with low nanomolar affinity, without interfering with the monomeric functional protein. This activity is translated into an unprecedented anti-aggregation potency and the ability to abrogate the oligomers toxicity. With a structure-function relationship in hand, we identified a human peptide expressed in the brain and in the gastrointestinal tract with exceptional binding, anti-aggregation, and detoxifying properties, which suggests it might play a protective role against synucleinopathies. The chemical entities we describe here represent a new therapeutic paradigm and are promising tools to assist diagnosis by selectively detecting α-synuclein pathogenic species in biofluids.

A targetable N-terminal motif orchestrates α-Synuclein oligomer to fibril conversion

“…A 6-fold symmetry and 5-layer organization provide the structural context to accommodate the 30 αS monomers known to form these oligomers (8,12,15). The stacking of five hexameric rings best explains the EM data, while the single set of resonances evidenced by ssNMR suggests that all αS subunits have equivalent conformations and chemical environments.…”

“…Tight molecular binders, such as antibodies, can stabilize and reduce the conformational heterogeneity of target proteins, facilitating 3D structure determination of otherwise intractable proteins and their complexes. Here we mimicked this approach and used the amphipathic 22-residue peptide phenol-soluble modulin α3 (PSMα3), a nanomolar binder of αS oligomers (KD = 6.67 nM; 1:1 PSMα3 per αS molecule at saturation) (15), as a tool to investigate their structural nature.…”

“…Isolated oligomer preparations were generated by incubating 800 µM of 13 C, 15 N labeled monomeric αS for 20 hours at 37 °C quiescently, followed by centrifugation-based fractionation as previously described (12). Oligomer-PSMα3 complexes were prepared by incubating oligomers with a 3-fold molar excess of PSMα3 and subsequent removal of the unbound peptide.…”

“…S9). The fact that PSMα3 stalls amyloid formation by blocking oligomer-to-fibril conversion (15) and the evidence that PSMα3 targets these αS motifs, suggest that the P1 and P2 regions are involved in this pivotal stage of amyloid formation. As expected, few low molecular weight species (isolation of this fraction is described in materials and methods) were visible at the endpoint of the amyloid assembly assay of WT aS (Fig.…”