Role of different regions of α-synuclein in the assembly of fibrils

Elucidating the details of the assembly of amyloid fibrils is a key step to understanding the mechanism of amyloid deposition diseases including Parkinson's disease. Although several models have been proposed, based on analyses of polypeptides and short peptides, a detailed understanding of the structure and mechanism of (x-synuclein fibrillation remains elusive. In this study, we used trypsin and endoproteinase GluC to digest intact a-synuclein fibrils and to analyze the detailed morphology of the resultant fibrils/remnants. We also created three mutants of (x-synuclein, in which the N-terminal and C-terminal regions were removed, both individually and in combination, and investigated the detailed morphology of the fibrils from these mutants. Our results indicate that the assembly of mature a-synuclein fibrils is hierarchical: protofilaments -> protofibrils -> mature fibrils. There is a core region of similar to 70 amino acids, from residues similar to 32 to 102, which comprises the beta-rich core of the protofilaments and fibrils. In contrast, the two terminal regions show no evidence of participating in the assembly of the protofilament core but play a key role in the interactions between the protofilaments, which is necessary for the fibril maturation.