Significance Converging evidence points to the build-up of phosphorylated α-synuclein (α-syn) at residue serine 129 (pS129) in Lewy body disease, suggesting its central role in the regulation of α-syn aggregation and neuronal degeneration. However, a comprehensive understanding of the role of α-syn phosphorylation at pS129 in α-synuclenopathies pathogenesis is still lacking. Herein, we study the phosphorylation incidence and its effect on α-syn aggregation propensity and cellular toxicity. Collectively, our data suggest that pS129 occurred subsequent to initial α-syn aggregation, lessened aggregation propensity, and attenuated cytotoxicity through diverse assays. Our findings highlight major implications for a better understanding of the role of a molecular modification on protein aggregation.

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Serine 129 and, to a lesser extent, serine 87 can appear phosphorylated in the intrinsically disordered protein human alpha-Synuclein (AS), a key player in Parkinson's disease, where it accumulates in proteinaceous aggregates. Intriguingly, both phosphorylations are located in a highly negative potential region of the protein. Here we used molecular simulation to provide insight in the selective phosphorylation by polo-like kinase 2 (PLK2), in both monomeric and fibrillar forms of AS. We suggest that phosphorylation does not impact on the structural determinants of the physiological AS conformational ensemble, as the phosphate group is mostly solvated. Our findings are consistent with experimental data on the non-acetylated, non-physiological form of the protein. The phosphate groups of pAS may also be solvated in the aggregated form.

The disordered nature of Intrinsically Disordered Proteins (IDPs) makes their structural ensembles particularly susceptible to changes in chemical environmental conditions, often leading to an alteration of their normal functions. A Radial Distribution Function (RDF) is considered a standard method for characterizing the chemical environment surrounding particles during atomistic simulations, commonly averaged over an entire or part of a trajectory. Given their high structural variability, such averaged information might not be reliable for IDPs. We introduce the Time-Resolved Radial Distribution Function (TRRDF), implemented in our open-source Python package SPEADI, which is able to characterize dynamic environments around IDPs. We use SPEADI to characterize the dynamic distribution of ions around the IDPs Alpha-Synuclein (AS) and Humanin (HN) from Molecular Dynamics (MD) simulations, and some of their selected mutants, showing that local ion–residue interactions play an important role in the structures and behaviors of IDPs.