Methionine oxidation in α-synuclein inhibits its propensity for ordered secondary structure

Abstract

Edited by Karen G. Fleming ␣-Synuclein (AS) is an intrinsically disordered protein highly expressed in dopaminergic neurons. Its amyloid aggregates are the major component of Lewy bodies, a hallmark of Parkinson's disease (PD). AS is particularly exposed to oxidation of its methionine residues, both in vivo and in vitro. Oxidative stress has been implicated in PD and oxidized ␣-synuclein has been shown to assemble into soluble, toxic oligomers, rather than amyloid fibrils. However, the structural effects of methionine oxidation are still poorly understood. In this work, oxidized AS was obtained by prolonged incubations with dopamine (DA) or epigallocatechin-3-gallate (EGCG), two inhibitors of AS aggregation, indicating that EGCG promotes the same final oxidation product as DA. The conformational transitions of the oxidized and non-oxidized protein were monitored by complementary biophysical techniques, including MS, ion mobility (IM), CD, and FTIR spectroscopy assays. Although the two variants displayed very similar structures under conditions that stabilize highly disordered or highly ordered states, differences emerged in the intermediate points of transitions induced by organic solvents, such as trifluoroethanol (TFE) and methanol (MeOH), indicating a lower propensity of the oxidized protein for forming either ␣or ␤-type secondary structures. Furthermore, oxidized AS displayed restricted secondary-structure transitions in response to dehydration and slightly amplified tertiary-structure transitions induced by ligand binding. This difference in susceptibility to induced folding could explain the loss of fibrillation potential observed for oxidized AS. Finally, site-specific oxidation kinetics point out a minor delay in Met-127 modification, likely due to the effects of AS intrinsic structure.

Effects of pharmacological modulators of α-synuclein and tau aggregation and internalization

“…This effect was not only reported for aSyn, but also for other amyloidogenic proteins, such as AB and γ-synuclein (gSyn) 16 , 61 , 62 . Such effects are in agreement with the proposed mechanism of action for EGCG, whereby it mediates the reorientation of bonds between ordered protein molecules, leading to amyloid remodeling and the appearance of unordered, amorphous protein aggregates 17 , 63 . Additionally, similar results to those obtained here for anle138b and EGCG were obtained for the aggregation inhibitor SynuCleanD, which decreases aSyn aggregation in H4 neuroglioma cells.…”

Metal ions shape α-synuclein

“…The intermediate 8+ ion will be used here as a representative state in order to monitor shifts in the conformational ensemble upon metal ion binding. The 8+ charge state demonstrates a characteristic pattern with four prominent conformational families in the CCS range of 2200-3000 Å 2 , which have been described before 52 .…”

One- and Two-Electron Oxidations of β-Amyloid25-35 by Carbonate Radical Anion (CO3•−) and Peroxymonocarbonate (HCO4−): Role of Sulfur in Radical Reactions and Peptide Aggregation

“…Noteworthily, also the inhibition of fibrillation of α-synuclein is mediated by methionine oxidation. It has been suggested that α-synuclein completely oxidized to its Met residues shows a reduced propensity to form amyloid fibrils, probably related to the interference of MetSO residues in oxidized protein to form ordered β-type secondary structures [51].…”