The α-synuclein hereditary mutation E46K unlocks a more stable, pathogenic fibril structure

Abstract

Aggregation of α-synuclein is a defining molecular feature of Parkinson’s disease, Lewy body dementia, and multiple systems atrophy. Hereditary mutations in α-synuclein are linked to both Parkinson’s disease and Lewy body dementia; in particular, patients bearing the E46K disease mutation manifest a clinical picture of parkinsonism and Lewy body dementia, and E46K creates more pathogenic fibrils in vitro. Understanding the effect of these hereditary mutations on α-synuclein fibril structure is fundamental to α-synuclein biology. We therefore determined the cryo-electron microscopy (cryo-EM) structure of α-synuclein fibrils containing the hereditary E46K mutation. The 2.5-Å structure reveals a symmetric double protofilament in which the molecules adopt a vastly rearranged, lower energy fold compared to wild-type fibrils. We propose that the E46K misfolding pathway avoids electrostatic repulsion between K46 and K80, a residue pair which form the E46-K80 salt bridge in the wild-type fibril structure. We hypothesize that, under our conditions, the wild-type fold does not reach this deeper energy well of the E46K fold because the E46-K80 salt bridge diverts α-synuclein into a kinetic trap—a shallower, more accessible energy minimum. The E46K mutation apparently unlocks a more stable and pathogenic fibril structure.

Parkinson’s disease associated mutation E46K of α-synuclein triggers the formation of a distinct fibril structure

“…Furthermore, a recent study on brainderived α-syn fibril showed that in vivo cofactors can participate into α-syn fibril structure and introduce more polymorphs 36 . Recently, several fibril structures formed by inherited α-syn mutants have bee reported including Ac-A53T 37 , H50Q 24 , and E46K 23,38 . The Ac-A53T and H50Q fibrils exhibit similar morphology, and α-syn monomer in these structures folds similarly to that in the Ac-WT fibril ( Supplementary Fig.…”

A series of helical α-synuclein fibril polymorphs are populated in the presence of lipid vesicles

“…Many approaches describe structures gained via recombinant means under in vitro conditions [2][3][4][5]7,9,10 . Others have employed the use of lipids during in vitro experiments, since this is critical to αS function in situ 6,[11][12][13][14][15][16][17] . More recent studies are emerging in which aggregates of αS from specific neurodegenerative diseases and key regions of the brain are isolated in small quantities 8,18 .…”

Multiplicity of α-Synuclein Aggregated Species and Their Possible Roles in Disease

“…The number and location of β-strands within this region, however, varies between fibril polymorphs generated under different solution conditions, with the ionic strength, the presence of polyanions or the pH of the solution as main factors for fibril structure variability. These observations, therefore, already highlight the relevance of electrostatic interactions in the intramolecular and intermolecular forces that define the overall structure in the different amyloid polymorphs [119,124,125]. Two regions within the amyloid core have been suggested to be important for stabilizing the amyloid structure [123], concretely 71-82 region, which was also found to be essential for the initiation of the aggregation process [126], and 45-57 region, where most of the pathological point mutations are located.…”

“…The presence of such mutations were suggested to affect severely the protofilament arrangement and then the stability of mature fibrils, which was correlated with the potential increase in the fraction of toxic oligomeric species within the cells [125]. The E46K pathological mutation, however, was later reported to adopt a significantly different amyloid fold as compared to the amyloid structure adopted by the WT protein at similar conditions [124,125]. The acquisition of this alternative fibril kernel conformation by the E46K mutation results in a significantly higher propensity to seed the formation of new fibrils as compared to the WT fibrils [124,125], which could influence the speed of αS pathology spreading.…”

“…The E46K pathological mutation, however, was later reported to adopt a significantly different amyloid fold as compared to the amyloid structure adopted by the WT protein at similar conditions [124,125]. The acquisition of this alternative fibril kernel conformation by the E46K mutation results in a significantly higher propensity to seed the formation of new fibrils as compared to the WT fibrils [124,125], which could influence the speed of αS pathology spreading. It is interesting to note that the E46K mutation seems to be the only hereditary αS mutation that manifests in a clinical picture closer to DLB; the other mutations being more associated to PD.…”