Two new polymorphic structures of alpha-synuclein solved by cryo-electron microscopy

Intracellular inclusions rich in alpha-synuclein are a hallmark of several neuropathological diseases including Parkinsons disease (PD). We here report two new polymorphic atomic structures of alpha-synuclein fibrils termed polymorphs 2a and 2b, at 3.0 [A] and 3.4 [A] resolution, respectively. These polymorphs show a radically different structure compared to previously reported polymorphs. The new structures have a 10 nm fibril diameter and are composed of two protofilaments which interact via intermolecular salt-bridges between amino acids K45, E57 (polymorph 2a) or E46 (polymorph 2b). The non-amyloid component (NAC) region of alpha-synuclein is fully buried by previously non-described interactions with the N-terminus. A hydrophobic cleft, the location of familial PD mutation sites, and the nature of the protofilament interface now invite to formulate hypotheses about fibril formation, growth and stability. Impact statementTwo new polymorphic structures of recombinant human alpha-synuclein fibrils show striking differences to previous structures, while familial PD mutation sites remain crucial for protofilament interaction and fibril stability.