Abstract
α-Synuclein is an intrinsically disordered protein that can self-aggregate and plays a major role in Parkinson’s disease (PD). Elevated levels of certain metal ions are found in protein aggregates in neurons of people suffering from PD, and environmental exposure has also been linked with neurodegeneration. Importantly, cellular interactions with metal ions, particularly Ca2+, have recently been reported as key for α-synuclein’s physiological function at the pre-synapse. Here we study effects of metal ion interaction with α-synuclein at the molecular level, observing changes in the conformational behaviour of monomers, with a possible link to aggregation pathways and toxicity. Using native nano-electrospray ionisation ion mobility-mass spectrometry (nESI-IM-MS), we characterize the heterogeneous interactions of alkali, alkaline earth, transition and other metal ions and their global structural effects on α-synuclein. Different binding stoichiometries found upon titration with metal ions correlate with their specific binding affinity and capacity. Subtle conformational effects seen for singly charged metals differ profoundly from binding of multiply charged ions, often leading to overall compaction of the protein depending on the preferred binding sites. This study illustrates specific effects of metal coordination, and the associated electrostatic charge patterns, on the complex structural space of the intrinsically disordered protein α-synuclein.
Highlights
Α-Synuclein is an intrinsically disordered protein that can self-aggregate and plays a major role in Parkinson’s disease (PD)
In the ESI process, the number of proton charges found on a protein when released from the liquid droplet, is believed to correlate with the solvent accessible surface area (SASA) and the conformation at that moment
This work highlights the capability of native nESI-IM-MS to capture the heterogeneous conformational space of biologically relevant targets that are challenging to study with more conventional biophysical techniques
Summary
Α-Synuclein is an intrinsically disordered protein that can self-aggregate and plays a major role in Parkinson’s disease (PD). In vivo, the protein needs to adapt to different physiological environments where it experiences various biophysical conditions, such as pH, salt and metal ion concentrations[7,8,9] These external factors can be a trigger for structural transitions and potentially reshape the conformational space of α-syn[10,11,12,13]. Metal ions can play an important role in this process, for example the charge distribution of the negatively charged C-terminal region can be profoundly affected by Ca2+ binding that can modulate subsequent protein-membrane interactions[8]. IDPs have been described as being more sensitive to altered charge distributions than globular, folded proteins, with charge patterns and densities suggested as key factors determining their conformational s pace[29] Environmental factors such as pH, temperature, ionic strength and crowding agents can play an important role as w ell[37,38,39]
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