2003) or by changing tyrosine residues to alanine (Ulrih et al. 2008). It is also Selleckchem Buparlisib reported that an increased tendency to form fibrils was observed for C-terminal truncated mutants of α-syn both in vitro (Crowther et al. 1998; Murray et al. 2003; Hoyer et al. 2004; Levitan et al. 2011) and in vivo (Li et al. 2005; Liu Inhibitors,research,lifescience,medical et al. 2005). About 10–30% of α-syn found in Lewy bodies is truncated at the C-terminal (Li et al. 2005). These findings suggest that the C-terminal region of α-syn
is important for fibril formation, and hence, further study of this region is useful for understanding the steps leading to the onset of Parkinson’s disease. In this study, in order to Inhibitors,research,lifescience,medical further explore the role of C-terminal region of α-syn, we probed the relative contributions of negatively charged amino acid side chains and the tyrosine residues in fibril nucleus formation and elongation. Confirming earlier studies, various deletion mutants of α-syn readily formed amyloid fibrils compared with the wild-type α-syn (Syn-wt). The specific contribution of negatively charged side chains
was determined by neutralizing these charges through Asp/Glu Inhibitors,research,lifescience,medical to Asn substitutions. We found that negatively charged side chains located in the C-terminal region of α-syn act to retard fibril formation. On the other hand, a specific tyrosine residue, Tyr136, displayed an active role in promoting α-syn fibrillation, as demonstrated in various Tyr136Ala mutations of α-syn and derivatives. Furthermore, mutation of Tyr136 to various other amino acids revealed that aromatic residues located at this position promote fibril formation. Inhibitors,research,lifescience,medical Finally, in mutants that combined
Inhibitors,research,lifescience,medical both charge neutralization and tyrosine substitution, we found that these two modulating factors acted mostly independently in influencing fibril formation, with one glaring exception. This exception served to highlight an additional level of complexity in the fibril formation process of α-syn. Materials and Methods Expression and preparation of wild-type and mutant proteins of α-syn The human α-syn gene was cloned into pET vector to make pET-SYN plasmid and expressed in Escherichia coli BLR(DE3) (Novagen, Darmstadt, Germany), and Syn-wt Resminostat was purified as described previously (Yagi et al. 2005). C-terminal truncated or altered mutants of α-syn were constructed by using the QuikChange site-directed mutagenesis kit (Stratagene, Santa Clara, California), using pET-SYN as the template. Amino acid sequences of the C-terminal region of all α-syn proteins used in this study are summarized in Table 1. The successful construction of each mutant was confirmed by DNA sequence analysis of the entire α-syn coding region, and protein expression was checked by SDS–PAGE (12.