Perturbation in Long-Range Contacts Modulates the Kinetics of Amyloid Formation in α-Synuclein Familial Mutants

The characteristic cross-β-sheet-rich amyloid fibril formation by intrinsically disordered α-synuclein proteins is one of the pathological hallmarks of Parkinson's disease. Although unstructured in solution, the presence of autoinhibitory long-range contacts in monomeric form prevents protein aggregation. Out of the various factors that affect the rate of amyloid formation, familial mutations play an important role in α-synuclein aggregation. Even though these mutations are believed to form an aggregation-prone intermediate by perturbing these contacts, the correlation between perturbation and rate of fibril formation is not very straightforward. A combination of solution and solid-state NMR in conjunction with other biophysical methods has been used to identify the underlying mechanism behind the anomaly in the rate of aggregation for the novel mutants H50Q (fast aggregating) and G51D (slow aggregating). Perturbation of long-range contacts at the mutation sites and C-termini in all of the six familial mutants of α-synuclein during the diseased condition (acidic pH) was observed. These contacts get rearranged at physiological pH resulting in the shielding of mutation sites. Additional contacts at the mutation site in a slow aggregating mutant could be the reason for slower aggregation. Indeed, these contacts provide more rigidity to the monomeric G51D. Nonetheless, these mutations did not alter the overall secondary structure. The differential pattern of the long-range contacts at the monomeric level resulted in the perturbation of the fibrillar-core region, which was evident in the solid-state NMR spectra. Our results provide valuable insights in understanding the effect of long-range contacts on the aggregation of α-synuclein and its mutants.