Nucleation of α-Synuclein Amyloid Fibrils Induced by Cross-Interaction with β-Hairpin Peptides Derived from Immunoglobulin Light Chains

Heterologous interactions between different amyloid-forming proteins, also called cross-interactions, may have a critical impact on disease-related amyloid formation. beta-hairpin conformers of amyloid-forming proteins have been shown to affect homologous interactions in the amyloid self-assembly process. Here, we applied two beta-hairpin-forming peptides derived from immunoglobulin light chains as models to test how heterologous beta-hairpins modulate the fibril formation of Parkinson's disease-associated protein alpha-synuclein (alpha Syn). The peptides SMAhp and LENhp comprise beta-strands C and C' of the kappa 4 antibodies SMA and LEN, which are associated with light chain amyloidosis and multiple myeloma, respectively. SMAhp and LENhp bind with high affinity to the beta-hairpin-binding protein beta-wrapin AS10 according to isothermal titration calorimetry and NMR spectroscopy. The addition of SMAhp and LENhp affects the kinetics of alpha Syn aggregation monitored by Thioflavin T (ThT) fluorescence, with the effect depending on assay conditions, salt concentration, and the applied beta-hairpin peptide. In the absence of agitation, substoichiometric concentrations of the hairpin peptides strongly reduce the lag time of alpha Syn aggregation, suggesting that they support the nucleation of alpha Syn amyloid fibrils. The effect is also observed for the aggregation of alpha Syn fragments lacking the N-terminus or the C-terminus, indicating that the promotion of nucleation involves the interaction of hairpin peptides with the hydrophobic non-amyloid-beta component (NAC) region.

Automated summary

Heterologous interactions between different amyloid-forming proteins can have a significant impact on disease-related amyloid formation. In this study, researchers tested how heterologous beta-hairpins derived from immunoglobulin light chains modulate the fibril formation of Parkinson's disease-associated protein alpha-synuclein. They found that the addition of these beta-hairpins affects the kinetics of alpha-synuclein aggregation, suggesting they support the nucleation of amyloid fibrils.