Binding of Dopamine to Alpha-Synuclein is Mediated by Specific Conformational States

Abstract

Parkinson’s disease is the second most common neurodegenerative disorder, in which both alpha-synuclein (α-syn) and dopamine (DA) have a critical role. α-Syn is known to be natively unstructured in equilibrium with subpopulations of more compact structures. It is these compact structures that are thought to be linked to amyloid formation. In the presence of DA, α-syn yields a diverse range of SDS-resistant, non-amyloid oligomers, however the precursor state conformation has not been established. Here, three DA molecules have been observed to bind per α-syn monomer by electrospray-ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS). Each of these DA molecules binds exclusively to the extended conformation of α-syn, and binding is not observed in the compact state of the protein. Measurements of collisional cross sectional areas show that the incremental uptake of DA pushes the protein towards a highly extended population, becoming fully populated upon the binding of three DA ligands. Tyrosine (Tyr) as a closely related structural analog, exhibited limited binding to the protein as compared with DA, with a maximum of two ligands being observed. Those Tyr ligands that do bind were observed as adducts to the extended conformation akin to DA. These findings suggest DA is able to modulate α-syn self-assembly by inducing the population of a highly extended state.FigureᅟElectronic supplementary materialThe online version of this article (doi:10.1007/s13361-013-0676-z) contains supplementary material, which is available to authorized users.

Distinct higher-order α-synuclein oligomers induce intracellular aggregation

“…The monomeric form of α-syn is considered a natively disordered protein as it displays considerable conformational heterogeneity [35,36]. Analysis of WT α-syn before the addition of cofactors and ethanol revealed a primarily extended population (charge state ions + 8 to + 18) and a sub-population of a more compact conformational series (charge state ions + 6 to + 8) with multiple overlapping features consistent with previous data [34,37] (Figure 1). Critically, oligomeric forms were not detected immediately upon solvation and the addition of 20 % ethanol, indicating that oligomers assemble as a result of the preparation protocols and are not induced by the act of spectral acquisition.…”

“…In vivo, oligomers characterized recently by number and brightness analysis in live SH-SH5Y cells also show a similar size range encompassing maximum 6 + − 4-mers, similar to our observations [50]. α-Syn is known to co-populate a range of conformational states as observed by ESI-IMS-MS. Our previous ESI-IMS-MS analysis of wild-type α-syn revealed a primarily extended population (∼2482 + − 159 Å) and a subpopulation of two compact conformational series (∼1851 + − 276 Å) with multiple overlapping features and a less observable dimeric species under native conditions [37] in accordance with previously published research [34]. The Barran group recently reported that α-syn displays a broad CSD ranging from + 5 to + 21 with a of approximately 1600 Å.…”

Opposite Structural Effects of Epigallocatechin-3-gallate and Dopamine Binding to α-Synuclein

“…The results show a strong bias in favor of the highly charged ions. These data are in agreement with previous MS analyses of these complexes 21,22 . The extracted CSDs of the free and bound (Fig.…”

“…The interaction of EGCG and DA with AS has been investigated by several biophysical methods 6,9,20-24 , including native mass spectrometry [21][22][23] . Native mass spectrometry relies on gentle transfer of proteins and their complexes from solution into the gas phase of the mass spectrometer, without major structural rearrangements or disruption of non-covalent interactions [25][26][27][28] .…”

Molecular Basis for Structural Heterogeneity of an Intrinsically Disordered Protein Bound to a Partner by Combined ESI-IM-MS and Modeling

“…This trend is consistent with the lowest charge state (8+ in this case) corresponding to the most compact species in the original ensemble and to the species with lowest interference of Coulomb repulsions upon transfer to the gas phase. Interestingly, at higher charge states (Figure 4c), the structurally heterogeneous nature of the complex is maintained, whereas for a fully disordered protein such as alpha-synuclein this converges into a single arrival-time distribution for higher charge states [74]. Altogether, these results suggest that both the open and closed states of the complex should be described as conformational ensembles.…”