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

Abstract

Amyloid fibril formation of α-synuclein (αS) is associated with multiple neurodegenerative diseases, including Parkinson’s disease (PD). Growing evidence suggests that progression of PD is linked to cell-to-cell propagation of αS fibrils, which leads to seeding of endogenous intrinsically disordered monomer via templated elongation and secondary nucleation. A molecular understanding of the seeding mechanism and driving interactions is crucial to inhibit progression of amyloid formation. Here, using relaxation-based solution NMR experiments designed to probe large complexes, we probe weak interactions of intrinsically disordered acetylated-αS (Ac-αS) monomers with seeding-competent Ac-αS fibrils and seeding-incompetent off-pathway oligomers to identify Ac-αS monomer residues at the binding interface. Under conditions that favor fibril elongation, we determine that the first 11 N-terminal residues on the monomer form a common binding site for both fibrils and off-pathway oligomers. Additionally, the presence of off-pathway oligomers within a fibril seeding environment suppresses seeded amyloid formation, as observed through thioflavin-T fluorescence experiments. This highlights that off-pathway αS oligomers can act as an auto-inhibitor against αS fibril elongation. Based on these data taken together with previous results, we propose a model in which Ac-αS monomer recruitment to the fibril is driven by interactions between the intrinsically disordered monomer N terminus and the intrinsically disordered flanking regions (IDR) on the fibril surface. We suggest that this monomer recruitment may play a role in the elongation of amyloid fibrils and highlight the potential of the IDRs of the fibril as important therapeutic targets against seeded amyloid formation.

The N terminus of α-synuclein dictates fibril formation

“…From a mechanistic standpoint, two recent studies also have highlighted the involvement of N-terminal residues in fibril formation. Specifically, residues 1–11 ( 42 ) and 1–12 ( 43 ) are identified in monomer addition to the ends of seeds (i.e., elongation) and monomer binding to the fibril surface (i.e., secondary nucleation), respectively. These results are in agreement with our cross-propagation experiments using ΔN-α-syn fibrils, in which the effect of the first 13 residues is clearly documented ( Fig.…”

Structural and Functional Insights into α-Synuclein Fibril Polymorphism

“…Furthermore, α-Syn has been shown to undergo numerous PTMs, like phosphorylation, methionine oxidation, acetylation, nitration, etc., which are directly associated with its aggregation and cytotoxicity [94,115,267,268]. As pS129 is the most common PTM and the main form of α-Syn in the inclusion bodies, it may cause strain formation in α-Syn in vivo.…”

Tannic Acid Inhibits α-Synuclein Amyloid Fibril Formation via Binding to the Monomer N-terminal Domain

“…The N-terminus of aS has recently been found to mediate the interaction between the IDP monomers and the disordered regions of the fibril that initiates the amyloid seeding process [46,47]. The interaction with the disordered regions of amyloid fibrils that make up their "fuzzy" surface is increasingly being identified to be important in more and more amyloid systems [48].…”