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

Amyloid formation by -synuclein (Syn) occurs in Parkinsons disease, multiple system atrophy, and dementia with Lewy bodies. Deciphering the residues that regulate Syn 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 Syn to be important in the regulation of amyloid formation, including the non-amyloid-{beta} 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 Syn for both its physiological and pathological roles. Here, the role of residues 2-7 in the N-terminal region of Syn are investigated in terms of their ability to regulate amyloid fibril formation in vitro and in vivo. Deletion of these residues (Syn{Delta}N7) slows the rate of fibril formation in vitro and reduces the capacity of the protein to be recruited by wild-type (SynWT) fibril seeds, despite cryo-EM showing a fibril structure consistent with those of full-length Syn. Strikingly, fibril formation of Syn{Delta}N7 is not induced by liposomes, despite the protein binding to liposomes with similar affinity to SynWT. A Caenorhabditis elegans model also showed that Syn{Delta}N7::YFP forms few puncta and lacks motility and lifespan defects typified by expression of SynWT::YFP. Together, the results demonstrate the involvement of residues 2-7 of Syn 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 -synuclein (Syn) is associated with Parkinsons disease. Attempts to target Syn 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 Syn are identified as regulators of amyloid formation. Deletion of these residues slows lipid-independent assembly, ablates lipid-dependent amyloid formation in vitro, and prevents aggregation and its associated cellular toxicity in 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 Syn at the synapse.