As shown in Figure 2a, whereas Syn-wt Luminespib order formed amyloid fibrils after an 80-h incubation, all C-terminal truncated mutants formed fibrils much more quickly (~10–20 h), suggesting that deletion of negative charges from the C-terminal region caused a significant change

in the fibril formation rate under these conditions; a significant acceleration in fibril formation was observed even for Syn129, which had only four acidic amino acid residues deleted from the C-terminus. Figure 2 Fibril formation characteristics of the C-terminal truncated mutants. (a) and (b) Amyloid fibril formation monitored by ThioT binding assay. Conditions were 1 mg/mL protein in 25 mmol/L Tris–HCl buffer, pH 7.5, containing 0 mol/L (a) and 150 mmol/L … Inhibitors,research,lifescience,medical To observe in more detail differences caused by deleting some or all of the acidic amino acid residues from the α-syn Inhibitors,research,lifescience,medical C-terminus, fibril formation experiments were performed in buffer containing 150 mmol/L NaCl, a salt concentration that more closely resembles physiological conditions. At 150 mmol/L NaCl, as shown in Figure 2b, Syn103 formed fibrils most quickly, and Syn-wt was the slowest, although a large acceleration was observed for Syn-wt when compared to the reaction in 0 mol/L NaCl (from 80 to 25 h). In the presence of 150 mmol/L NaCl (Fig. 2b), the degree of acceleration correlated very well with the number of negative residues

Inhibitors,research,lifescience,medical deleted from the C-terminus. A similar correlation has been reported by Hoyer et al. (2004). Notably, as the rate of fibril extension (as monitored by the slope of ThioT fluorescence increase seen after the initial lag Inhibitors,research,lifescience,medical stage) was similar for all of the mutants and Syn-wt (Fig. 2b), it is likely that the removal of negative charges from the C-terminal region of α-syn mainly affects fibril nucleus formation. This correlation was also reported by Levitan et al. (2011) very recently. In Figure 2c, CD spectra and TEM images of Syn-wt and all mutant proteins after formation Inhibitors,research,lifescience,medical of fibrils are shown. In CD spectra, β-sheet-like structural characteristics were observed for all

proteins. In TEM images, although minute differences in morphology were observed depending on the mutant protein, linear fibers with similar dimensions (~20 nm in width) were observed. through In order to clarify the notion that the acceleration of nucleus formation is due only to changes in negative charge, rather than overall polypeptide length, we next prepared two charge-neutralized full-length α-syn mutants, Syn130-140CF and Syn119-140CF. Syn130-140CF is a full-length (140 AA) α-syn polypeptide in which four Glu residues and one Asp residue located between positions 130 and 140 have been replaced by the noncharged amino acid residue asparagine. In Syn119-140CF, six Glu and three Asp residues between positions 119 and 140 have been changed to Asn (Fig. 1 and Table 1). Fibril formation of these mutants were examined and compared with Syn-wt.