Mechanisms of enhanced aggregation and fibril formation of Parkinson's disease-related variants of α-synuclein

Aggregation of alpha-synuclein (alpha-syn) into amyloid fibrils is closely associated with Parkinson's disease (PD). Familial mutations or posttranslational truncations in alpha-syn are known as risk factor for PD. Here, we examined the effects of the PD-related A30P or A53T point mutation and C-terminal 123-140 or 104-140 truncation on the aggregating property of alpha-syn based on the kinetic and thermodynamic analyses. Thioflavin T fluorescence measurements indicated that A53T, Delta 123-140, and Delta 104-140 variants aggregated faster than WT alpha-syn, in which the A53T mutation markedly increases nucleation rate whereas the Delta 123-140 or Delta 104-140 truncation significantly increases both nucleation and fibril elongation rates. Ultracentrifugation and western blotting analyses demonstrated that these mutations or truncations promote the conversion of monomer to aggregated forms of alpha-syn. Analysis of the dependence of aggregation reaction of alpha-syn variants on the monomer concentration suggested that the A53T mutation enhances conversion of monomers to amyloid nuclei whereas the C-terminal truncations, especially the Delta 104-140, enhance autocatalytic aggregation on existing fibrils. In addition, thermodynamic analysis of the kinetics of nucleation and fibril elongation of alpha-syn variants indicated that both nucleation and fibril elongation of WT alpha-syn are enthalpically and entropically unfavorable. Interestingly, the unfavorable activation enthalpy of nucleation greatly decreases for the A53T and becomes reversed in sign for the C-terminally truncated variants. Taken together, our results indicate that the A53T mutation and the C-terminal truncation enhance alpha-syn aggregation by reducing unfavorable activation enthalpy of nucleation, and the C-terminal truncation further triggers the autocatalytic fibril elongation on the fibril surfaces.

Automated summary

The A53T mutation and C-terminal truncation enhance the aggregation of α-synuclein by reducing the unfavorable activation enthalpy of nucleation, and the truncation further triggers the autocatalytic fibril elongation on the fibril surfaces.