The C-terminal tail of \u03b1-synuclein protects against aggregate replication but is critical for oligomerization

Azad Farzadfard,Arun Kumar Somavarapu,Jannik Nedergaard Pedersen,Morten Agertoug Nielsen,Daniel Erik Otzen,Tuomas P J Knowles,Adam Frederik Sander,Louise Goksøyr,Jan Skov Pedersen,Parvez Alam,Georg Meisl

doi:10.1038/s42003-022-03059-8

Abstract

Aggregation of the 140-residue protein α-synuclein (αSN) is a key factor in the etiology of Parkinson’s disease. Although the intensely anionic C-terminal domain (CTD) of αSN does not form part of the amyloid core region or affect membrane binding ability, truncation or reduction of charges in the CTD promotes fibrillation through as yet unknown mechanisms. Here, we study stepwise truncated CTDs and identify a threshold region around residue 121; constructs shorter than this dramatically increase their fibrillation tendency. Remarkably, these effects persist even when as little as 10% of the truncated variant is mixed with the full-length protein. Increased fibrillation can be explained by a substantial increase in self-replication, most likely via fragmentation. Paradoxically, truncation also suppresses toxic oligomer formation, and oligomers that can be formed by chemical modification show reduced membrane affinity and cytotoxicity. These remarkable changes correlate to the loss of negative electrostatic potential in the CTD and highlight a double-edged electrostatic safety guard.

Highlights

Aggregation of the 140-residue protein α-synuclein is a key factor in the etiology of Parkinson’s disease
SDS-PAGE analyses confirmed that the great majority of αSN had aggregated by the end of the reaction (Fig. S4). (Note that slightly incomplete levels of fibrillation will not affect the outcome of the analysis in Amylofit.) Transmission electron microscopy (TEM) demonstrated very similar architecture for the fibrils formed by the different truncation variants (Fig. S5)
Truncation of C-terminal domain (CTD) at positions 103, 118, and 129 or replacing anionic residues in CTD with neutral counterparts speeds up fibrillation[49]

Summary

Introduction

Aggregation of the 140-residue protein α-synuclein (αSN) is a key factor in the etiology of Parkinson’s disease. We study stepwise truncated CTDs and identify a threshold region around residue 121; constructs shorter than this dramatically increase their fibrillation tendency These effects persist even when as little as 10% of the truncated variant is mixed with the fulllength protein. Aggregation of αSN to form insoluble fibrils and smaller oligomeric species (αSOs), a process which is increased in different familial variants of Parkinson’s disease (PD)[2], is critical to the onset and development of PD. This involves neuronal toxicity propagated through the brain, presumably via the transmission of αSN aggregates from cell to cell[1]. CTD-specific antibodies ameliorate neurodegeneration pathology and behavior in PD-mice model and inhibit disease propagation[17]

Methods

Results

Conclusion