Complexation of NAC-Derived Peptide Ligands with the C‑Terminus of α‑Synuclein Accelerates Its Aggregation

Aggregation of α-synuclein (α-Syn) into neurotoxic oligomers and amyloid fibrils is suggested to be the pathogenic mechanism for Parkinson’s disease (PD). Recent studies have indicated that oligomeric species of α-Syn are more cytotoxic than their mature fibrillar counterparts, which are responsible for dopaminergic neuronal cell death in PD. Therefore, the effective therapeutic strategies for tackling aggregation-associated diseases would be either to prevent aggregation or to modulate the aggregation process to minimize the formation of toxic oligomers during aggregation. In this work, we showed that arginine-substituted α-Syn ligands, based on the most aggregation-prone sequence of α-Syn, accelerate the protein aggregation in a concentration-dependent manner. To elucidate the mechanism by which Arg-substituted peptides could modulate α-Syn aggregation kinetics, we performed surface plasmon resonance (SPR) spectroscopy, nuclear magnetic resonance (NMR) studies, and all-atom molecular dynamics (MD) simulation. The SPR analysis showed a high binding potency of these peptides with α-Syn but one that was nonspecific in nature. The two-dimensional NMR studies suggest that a large stretch within the C-terminus of α-Syn displays a chemical shift perturbation upon interacting with Arg-substituted peptides, indicating C-terminal residues of α-Syn might be responsible for this class of peptide binding. This is further supported by MD simulation studies in which the Arg-substituted peptide showed the strongest interaction with the C-terminus of α-Syn. Overall, our results suggest that the binding of Arg-substituted ligands to the highly acidic C-terminus of α-Syn leads to reduced charge density and flexibility, resulting in accelerated aggregation kinetics. This may be a potentially useful strategy while designing peptides, which act as α-Syn aggregation modulators

The Familial α‑Synuclein A53E Mutation Enhances Cell Death in Response to Environmental Toxins Due to a Larger Population of Oligomers

Amyloid formation of α-synuclein (α-Syn) and its familial mutations are directly linked with Parkinson’s disease (PD) pathogenesis. Recently, a new familial α-Syn mutation (A53E) was discovered, associated with an early onset aggressive form of PD, which delays α-Syn aggregation. When we overexpressed wild-type (WT) and A53E proteins in cells, showed neither toxicity nor aggregate formation, suggesting merely overexpression may not recapitulate the PD phenotype in cell models. We hypothesized that cells expressing the A53E mutant might possess enhanced susceptibility to PD-associated toxicants compared to that of the WT. When cells were treated with PD toxicants (dopamine and rotenone), cells expressing A53E showed more susceptibility to cell death along with compromised mitochondrial potential and an increased production of reactive oxygen species. The higher toxicity of A53E could be due to more oligomers being formed in cells as confirmed by a dot blot assay using amyloid specific OC and A11 antibody and using an <i>in vitro</i> aggregation study. The cellular model presented here suggests that along with familial mutation, environmental and other cellular factors might play a crucial role in dictating PD pathogenesis

Comparison of Kinetics, Toxicity, Oligomer Formation, and Membrane Binding Capacity of α‑Synuclein Familial Mutations at the A53 Site, Including the Newly Discovered A53V Mutation

The involvement of α-synuclein (α-Syn) amyloid formation in Parkinson’s disease (PD) pathogenesis is supported by the discovery of α-Syn gene (SNCA) mutations linked with familial PD, which are known to modulate the oligomerization and aggregation of α-Syn. Recently, the A53V mutation has been discovered, which leads to late-onset PD. In this study, we characterized for the first time the biophysical properties of A53V, including the aggregation propensities, toxicity of aggregated species, and membrane binding capability, along with those of all familial mutations at the A53 position. Our data suggest that the A53V mutation accelerates fibrillation of α-Syn without affecting the overall morphology or cytotoxicity of fibrils compared to those of the wild-type (WT) protein. The aggregation propensity for A53 mutants is found to decrease in the following order: A53T > A53V > WT > A53E. In addition, a time course aggregation study reveals that the A53V mutant promotes early oligomerization similar to the case for the A53T mutation. It promotes the largest amount of oligomer formation immediately after dissolution, which is cytotoxic. Although in the presence of membrane-mimicking environments, the A53V mutation showed an extent of helix induction capacity similar to that of the WT protein, it exhibited less binding to lipid vesicles. The nuclear magnetic resonance study revealed unique chemical shift perturbations caused by the A53V mutation compared to those caused by other mutations at the A53 site. This study might help to establish the disease-causing mechanism of A53V in PD pathology