␣-Synuclein is one of the causative proteins of familial Parkinson disease, which is characterized by neuronal inclusions named Lewy bodies. Lewy bodies include not only ␣-synuclein but also aggregates of other proteins. This fact raises a question as to whether the formation of ␣-synuclein amyloid fibrils in Lewy bodies may occur via interaction with fibrils derived from different proteins. To probe this hypothesis, we investigated in vitro fibril formation of human ␣-synuclein in the presence of preformed fibril seeds of various different proteins. We used three proteins, Escherichia coli chaperonin GroES, hen lysozyme, and bovine insulin, all of which have been shown to form amyloid fibrils. Very surprisingly, the formation of ␣-synuclein amyloid fibril was accelerated markedly in the presence of preformed seeds of GroES, lysozyme, and insulin fibrils. The structural characteristics of the natively unfolded state of ␣-synuclein may allow binding to various protein particles, which in turn triggers the formation (extension) of ␣-synuclein amyloid fibrils. This finding is very important for understanding the molecular mechanism of Parkinson disease and also provides interesting implications into the mechanism of transmissible conformational diseases.

No abstract

α-Synuclein (140 amino acids), one of the causative proteins of Parkinson's disease, forms amyloid fibrils in brain neuronal cells. In order to further explore the contributions of the C-terminal region of α-synuclein in fibril formation and also to understand the overall mechanism of fibril formation, we reduced the number of negatively charged residues in the C-terminal region using mutagenesis. Mutants with negative charges deleted displayed accelerated fibril formation compared with wild-type α-synuclein, demonstrating that negative charges located in the C-terminal region of α-synuclein modulate fibril formation. Additionally, when tyrosine residues located at position 125, 133, and 136 in the C-terminal region were changed to alanine residue(s), we found that all mutants containing the Tyr136Ala mutation showed delays in fibril formation compared with wild type. Mutation of Tyr136 to various amino acids revealed that aromatic residues located at this position act favorably toward fibril formation. In mutants where charge neutralization and tyrosine substitution were combined, we found that these two factors influence fibril formation in complex fashion. These findings highlight the importance of negative charges and aromatic side chains in the C-terminal region of α-synuclein in fibril formation.

No abstract

No abstract