Abnormal aggregation of α-synuclein, an intrinsically disordered protein in Lewy bodies, is considered a hallmark of Parkinson's disease (PD). The mechanisms underlying abnormal α-synuclein aggregation, however, are yet to be understood. Protein disulfide isomerase (PDI) is an important molecular chaperone in the endoplasmic reticulum, which can prevent disordered protein forming aggregation. PDI is shown to be overexpressed in the brain of PD patients, but with reduced activity due to S-nitrosylation of the cysteine residues in the active site. In vitro experiments have demonstrated that PDI can inhibit the aggregation of α-synuclein with unknown mechanisms. Hence, it may be of importance to study the inhibition mechanisms of PDI on α-synuclein aggregation. In this study, the interaction between α-synuclein and PDI was studied by NMR spectroscopy. It was found that the binding sites between the two are located on the N-terminal of α-synuclein. A variant PDI (PDI C-S) was prepared, in which all six cysteines were mutated to serines. It was found that the binding sites between PDI C-S and α-synuclein are located on the C-terminus of α-synuclein. The results of thioflavin T (ThT) fluorescence experiment showed that the inhibition activity of PDI C-S on α-synuclein aggregation was lower than the wild type, suggesting that wild type PDI may inhibit α-synuclein aggregation through binding to its N-terminal.
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