Structural Features and Toxicity of α-Synuclein Oligomers Grown in the Presence of DOPAC

Abstract

The interplay between α-synuclein and dopamine derivatives is associated with oxidative stress-dependent neurodegeneration in Parkinson’s disease (PD). The formation in the dopaminergic neurons of intraneuronal inclusions containing aggregates of α-synuclein is a typical hallmark of PD. Even though the biochemical events underlying the aberrant aggregation of α-synuclein are not completely understood, strong evidence correlates this process with the levels of dopamine metabolites. In vitro, 3,4-dihydroxyphenylacetaldehyde (DOPAL) and the other two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylethanol (DOPET), share the property to inhibit the growth of mature amyloid fibrils of α-synuclein. Although this effect occurs with the formation of differently toxic products, the molecular basis of this inhibition is still unclear. Here, we provide information on the effect of DOPAC on the aggregation properties of α-synuclein and its ability to interact with membranes. DOPAC inhibits α-synuclein aggregation, stabilizing monomer and inducing the formation of dimers and trimers. DOPAC-induced oligomers did not undergo conformational transition in the presence of membranes, and penetrated the cell, where they triggered autophagic processes. Cellular assays showed that DOPAC reduced cytotoxicity and ROS production induced by α-synuclein aggregates. Our findings show that the early radicals resulting from DOPAC autoxidation produced covalent modifications of the protein, which were not by themselves a primary cause of either fibrillation or membrane binding inhibition. These findings are discussed in the light of the potential mechanism of DOPAC protection against the toxicity of α-synuclein aggregates to better understand protein and catecholamine biology and to eventually suggest a scaffold that can help in the design of candidate molecules able to interfere in α-synuclein aggregation.

3,4‐Dihydroxyphenylethanol and 3,4‐dihydroxyphenylacetic acid affect the aggregation process of E46K variant of α‐synuclein at different extent: Insights into the interplay between protein dynamics and catechol effect

“…Moreover, DOPAC‐induced oligomers activate lysosomal activity favoring the clearance of Syn aggregates and attenuating Syn build‐up within Syn‐exposed cells. Finally, they reduce the ability of Syn to interact with lipid membranes 35,37 . In this study, HDX‐MS and SEC data show that the monomer opening effect induced by catechols is preserved during aggregation and a significant fraction of extended and relaxed conformation is maintained.…”

“…To avoid the methionine oxidation and to exclude this parameter in the evaluation of the effects of catechols on the aggregation properties of E46K, catalase was added to the aggregation mixture. The experiments were conducted comparing side by side the results with those obtained with the wild‐type protein (see also references 36 , 37 ). Different times of incubation have been tested (0, 48, 72, and 192 hr) corresponding to lag phase, elongation phase, and stationary phase in the fibril formation process.…”

“…It was previously found that Syn, incubated in the presence of catechols, gave rise to off‐pathway oligomers, mainly dimers and trimers and these species are chemically modified for the formation of adducts due to the covalent reaction of either DOPAC or DOPET quinone with the side chains of Lys residues. 36 , 37 These two aspects were evaluated for E46K by size exclusion chromatography (SEC) and RP‐HPLC comparing the chromatograms of samples taken from the aggregation mixture in correspondence of time points where the mutant is expected to populate mainly transient oligomers or fibrils with those obtained for Syn. The large and insoluble aggregates were removed by centrifugation before loading the samples onto the SEC column.…”

“…Furthermore, catechols reduce the ROS produced by Syn aggregates that exhibited reduced interaction with cell membranes. 35 , 36 , 37 …”

“…Catechol‐induced protein species may be described as a protected and shielded population, whose structure is responsible for their overall biological and biophysical effects. Furthermore, catechols reduce the ROS produced by Syn aggregates that exhibited reduced interaction with cell membranes 35–37 …”