Aggregated and Monomeric α-Synuclein Bind to the S6′ Proteasomal Protein and Inhibit Proteasomal Function

Heather Snyder, Kwame Mensah, Catherine Theisler, Jack Lee, Andreas Matouschek, Benjamin Wolozin
2003 Journal of Biological Chemistry  
The accumulation of aggregated ␣-synuclein is thought to contribute to the pathophysiology of Parkinson's disease, but the mechanism of toxicity is poorly understood. Recent studies suggest that aggregated proteins cause toxicity by inhibiting the ubiquitin-dependent proteasomal system. In the present study, we explore how ␣-synuclein interacts with the proteasome. The proteasome exists as a 26 S and a 20 S species. The 26 S proteasome is composed of the 19 S cap and the 20 S core. Aggregated
more » ... core. Aggregated ␣-synuclein strongly inhibited the function of the 26 S proteasome. The IC 50 of aggregated ␣-synuclein for ubiquitin-independent 26 S proteasomal activity was 1 nM. Aggregated ␣-synuclein also inhibited 26 S ubiquitin-dependent proteasomal activity at a dose of 500 nM. In contrast, the IC 50 of aggregated ␣-synuclein for 20 S proteasomal activity was > 1 M. This suggests that aggregated ␣-synuclein selectively interacts with the 19 S cap. Monomeric ␣-synuclein also inhibited proteasomal activity but with lower affinity and less potency. Recombinant monomeric ␣-synuclein inhibited the activity of the 20 S proteasomal core with an IC 50 > 10 M, exhibited no inhibition of 26 S ubiquitin-dependent proteasomal activity at doses up to 5 M, and exhibited only partial inhibition (50%) of the 26 S ubiquitinindependent proteasomal activity at doses up to 10 mM. Binding studies demonstrate that both aggregated and monomeric ␣-synuclein selectively bind to the proteasomal protein S6, a subunit of the 19 S cap. These studies suggest that proteasomal inhibition by aggregated ␣-synuclein could be mediated by interaction with S6.
doi:10.1074/jbc.m208641200 pmid:12551928 fatcat:pprlmoh33bdslblmhloepjeffa