Phosphorylation of α‑Synuclein Fibrils at S129 Changes DNAJB1 Binding as Probed by Solid-State NMR.

Amyloid fibrils formed by the protein α-synuclein are implicated in the pathogenesis of synucleinopathies. In addition to their rigid cross-β core, these fibrils have intrinsically disordered regions on their surface, which are important for interactions with other cellular components, such as chaperones. Chaperones play a vital role in preventing and reversing amyloid formation in neurodegenerative diseases. How they recognize misfolded proteins is an active field of research. DNAJB1 is a cochaperone that recognizes fibrils and recruits other chaperones such as Hsp70 and Apg2, which collectively disaggregate fibrils formed by α-synuclein, tau, and huntingtin. Because DNAJB1 was reported to bind the C-terminus of α-synuclein and S129 in this C-terminus is predominantly phosphorylated in patient-derived fibrils, we wanted to determine the effect of this post-translational modification on DNAJB1 binding. Using electron micrographs, NMR spectroscopy, and binding assays, we show that phosphorylation at S129 reduces the dynamics of the intrinsically disordered C-terminus of α-synuclein fibrils and increases the binding of DNAJB1 to this very C-terminus. MD simulations further suggest that the reduced dynamics is due to increased interaction of the phosphorylated C-terminus with the fibril core. DNAJB1 binds the exact same region at the C-terminus, indicating the phosphorylation at S129 might have a dual effect of reducing fibril surface dynamics and increasing chaperone recognition.