(723g) Investigation of N-Terminal Segment Effects on ?-Synuclein Aggregation through Discontinuous Molecular Dynamics

The aggregation of human α-synuclein (ASyn) is associated with many neurodegenerative diseases called “synucleopathies” such as Parkinson’s disease, dementia with Lewy bodies and multiple system atrophy. Development of treatments for these diseases, which affect millions of people worldwide, requires in-depth understanding of the self-assembly process of the ASyn protein. Both the non-amyloid component (NAC) region of ASyn (residues 61-95) and the N-terminal region (residues 1-60), the latter of which contains seven familial mutations, are thought to play important roles in ASyn fibrillation.

Of the sixty residues in the ASyn N-terminal region, two segments P1 (residues 36-42) and P2 (residues 45-57) have been found experimentally to be modulators of the aggregation of the full length ASyn¹. Eliminating P1 resulted in inhibiting ASyn aggregation in a neutral pH environment. In acidic condition, inhibition was observed by removing both P1 and P2. As P1 is the key component at both conditions, our objective is to look closely at P1 self-assembly and determine which residues promote, and which residues inhibit aggregation.

We used Discontinuous Molecular Dynamics (DMD)/PRIME20 simulations to study self-assembly of P1, P2 and P3 (residues 36-57). Each segment was examined at a simulation condition that supports fibril formation. Simulations of P1 were run for a system containing 48 peptides at 310K and 20mM. Simulations of P2 and P3 were run for 24 peptide systems at 10mM and at temperatures of 307.6K and 330.5K, respectively. All three segments were found to form β-sheets in silico as expected based on their secondary structure propensity scores as determined by Kang et al.² The β-sheets were predominantly parallel and stacked in an antiparallel arrangement. The U-shape fibrils obtained from the P3 simulations form similar intramolecular interactions to the β-hairpin structure of ASyn residues 37-54 in complex with β-wrapin AS69 determined by Mirecka et al.³The results from these simulations are used as a baseline for comparison when mutations are considered.

To determine the role of each residue in the aggregation process, we looked at a series of point mutations within the P1 region. Simulations were run on P3 for better observation of the impact of P1 mutations on ASyn. The simulations results are in good agreement with the experimental results from our experimental collaborators. The L38A mutation tends to prevent aggregation which agrees with experimental results from our collaborators. Simulation and experiment both show that V40A mutation does not inhibit the aggregation of ASyn, but the aggregation rate of V40A was slower than that of the wild type. This research confirms the crucial role of P1 in modulating ASyn fibrillation and suggests that the P1 sequence could be modified to inhibit ASyn aggregation without alternating ASyn biological functions.

References:

1. Doherty et al. Struct. Mol. Biol. 27, 249-259 (2020).
2. Kang et al. Protein Science. 21, 911-917 (2012).
3. Mirecka et al. Angew. Int. Ed. 53, 4227-4230 (2014).