Residues 2-7 of α-synuclein regulate amyloid formation via lipid-dependent and -independent pathways

Abstract

AbstractAmyloid formation by α-synuclein (αSyn) occurs in Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. Deciphering the residues that regulate αSyn amyloid fibril formation will not only provide mechanistic insight, but may also reveal new targets to prevent and treat disease. Previous investigations have identified several regions of αSyn to be important in the regulation of amyloid formation, including the non-amyloid-β component (NAC), P1 region (residues 36-42), and residues in the C-terminal domain. Recent studies have also indicated the importance of the N-terminal region of αSyn for both its physiological and pathological roles. Here, the role of residues 2-7 in the N-terminal region of αSyn are investigated in terms of their ability to regulate amyloid fibril formationin vitroandin vivo. Deletion of these residues (αSynΔN7) slows the rate of fibril formationin vitroand reduces the capacity of the protein to be recruited by wild-type (αSynWT) fibril seeds, despite cryo-EM showing a fibril structure consistent with those of full-length αSyn. Strikingly, fibril formation of αSynΔN7 is not induced by liposomes, despite the protein binding to liposomes with similar affinity to αSynWT. ACaenorhabditis elegansmodel also showed that αSynΔN7::YFP forms few puncta and lacks motility and lifespan defects typified by expression of αSynWT::YFP. Together, the results demonstrate the involvement of residues 2-7 of αSyn in amyloid formation, revealing a new target for the design of amyloid inhibitors that may leave the functional role of the protein in membrane binding unperturbed.Significance StatementAmyloid formation of α-synuclein (αSyn) is associated with Parkinson’s disease. Attempts to target αSyn aggregation to treat synucleinopathies, thus far, have been unsuccessful. A better understanding of residues that regulate amyloid formation may reveal new targets for therapeutics. Here, six residues at the N-terminus of αSyn are identified as regulators of amyloid formation. Deletion of these residues slows lipid-independent assembly, ablates lipid-dependent amyloid formationin vitro, and prevents aggregation and its associated cellular toxicityin vivo. Importantly, these residues are not necessary for binding to synthetic membranes. The work reveals a new target for the prevention of synucleinopathies by disfavouring aggregation without perturbing membrane binding, a property considered to be essential for the physiological function of αSyn at the synapse.