Multi-Pronged Interactions Underlie Inhibition of α-Synuclein Aggregation by β-Synuclein

Abstract

The intrinsically disordered protein β-synuclein is known to inhibit the aggregation of its intrinsically disordered homolog, α-synuclein, which is implicated in Parkinson's disease. While β-synuclein itself does not form fibrils at the cytoplasmic pH 7.4, alteration of pH and other environmental perturbations are known to induce its fibrilization. However, the sequence and structural determinants of β-synuclein inhibition and self-aggregation are not well understood. We have utilized a series of domain-swapped chimeras of α-synuclein and β-synuclein to probe the relative contributions of the N-terminal, C-terminal, and the central non-amyloid-β component domains to the inhibition of α-synuclein aggregation. Changes in the rates of α-synuclein fibril formation in the presence of the chimeras indicate that the non-amyloid-β component domain is the primary determinant of self-association leading to fibril formation, while the N- and C-terminal domains play critical roles in the fibril inhibition process. Our data provide evidence that all three domains of β-synuclein together contribute to providing effective inhibition, and support a model of transient, multi-pronged interactions between IDP chains in both processes. Inclusion of such multi-site inhibitory interactions spread over the length of synuclein chains may be critical for the development of therapeutics that are designed to mimic the inhibitory effects of β-synuclein.

Increased Dynamics of α-Synuclein Fibrils by β-Synuclein Leads to Reduced Seeding and Cytotoxicity

“…We have used the N-terminally acetylated forms of αS and βS, since this post-translational modification is constitutively present in the native forms of these intrinsically disordered proteins 37,38 . Consistent with our previous work 33,35 , βS delays αS fibril formation in the Thioflavin T (ThT) aggregation assay (Fig. S1), whereby the co-incubation of αS with βS results in a longer lag time and slower growth kinetics compared with αS by itself.…”

“…We have previously investigated the sequence and domain level interactions that mediate the influence of βS on the aggregation and fibril formation of αS 33,34 . We have found that head-to-tail transient complexes between βS and αS 35 , mediated by multi-pronged N- and C-terminal interactions 33 , provide enough of a kinetic trap at the earliest stages of αS aggregation to slow down the assembly of αS into fibrils. However, even though βS slows down αS aggregation and reduces the overall αS fibril load in a concentration dependent manner 35,36 , it does not fully abolish αS fibril formation.…”

NMR unveils an N-terminal interaction interface on acetylated-α-synuclein monomers for recruitment to fibrils

“…The specificity of monomer-aggregate interactions at the termini is consistent with previous work by our laboratory (50,51) and others (52,53) on αS monomer-monomer interactions, which showed that transient IDP-IDP dimers are mediated by N-N or N-C terminal interactions. Recent in vitro and in cell studies have shown that both the N-and C-termini of αS influence the amyloid growth kinetics, morphologies of resultant fibrils, and capacity for seeding full-length αS (25)(26)(27).…”

Novel Mannitol-Based Small Molecules for Inhibiting Aggregation of α-Synuclein Amyloids in Parkinson's Disease

“…An attractive therapeutic strategy toward synucleopathies would be to reduce formation of toxic oligomers and fibrils of α-Syn. Various attempts have been made along these lines, including the use of β-synuclein and its fragments (Shaltiel-Karyo et al, 2010; Leitao et al, 2018; Williams et al, 2018), nanobodies (Butler et al, 2016; Iljina et al, 2017), peptides (Madine et al, 2008; Choi et al, 2011, 2018), chaperones (Dedmon et al, 2005; Zhang et al, 2011), polydopamine dendrimers (Milowska et al, 2011), molecular tweezer (Prabhudesai et al, 2012), metal chelation (Mounsey and Teismann, 2012; Finkelstein et al, 2017), and various natural and synthetic small molecules (Zhu et al, 2004; Kobayashi et al, 2006; Masuda et al, 2006; Bieschke et al, 2010; Bisaglia et al, 2010; Meng et al, 2010; Scherzer-Attali et al, 2012; Singh et al, 2013; Ardah et al, 2014; Pujols et al, 2018), yet no such therapeutic is currently available. The various agents used exhibit certain limitations, including degradation by proteases and inefficient crossing of the blood brain barrier (BBB) (Begley, 2004; Werle and Bernkop-Schnürch, 2006; Gabathuler, 2010).…”