MAPT and Parkinson disease: Therefore, in addition to oxidized proteins, the 20S proteasome may degrade a broad spectrum of native proteins, including tumor suppressors p21, p53, and p27 (Sheaff et al., 2000; Liu et al., 2003; Asher et al., 2005) and proteins associated with neurodegenerative diseases such as α-synuclein [Parkinson's Disease (PD)] and tau [Alzheimer's disease (AD)] (David et al., 2002; Liu et al., 2003).