Synphilin-1 (SNCAIP) is a presynaptic protein that associates with synaptic vesicles (Ribeiro et al. 2002). It is present in many types of cytoplasmic inclusions, where it colocalizes with alpha-synuclein (SNCA). It is associated with Parkinson's Disease (PD) because it is an intrinsic component of Lewy bodies (Wakabayashi et al. 2000) and a mutation of the SNCAIP gene has been identified in some PD patients (Marx et al. 2003), suggesting that accumulation of SNCAIP and its interaction with SNCA may be relevant for Lewy body formation in PD.
SNCAIP is ubiquitinated by several different E3 ubiquitin-ligases, including Parkin (PARK2). PARK2 overexpression with SNCAIP in cell culture leads to the formation of protein aggregates (Chung et al. 2001). PARK2 preferentially mediates the addition of lysine-63 (K63)-linked polyubiquitination of SNCAIP (Lim et al. 2005). This leads to SNCAIP degradation only at an unusually high PARK2 to SNCAIP ratio (Lim et al. 2005). K63-linked ubiquitination may be a signal that leads to the degradation of inclusions by autophagy when the ubiquitin-proteasome system is dysfunctional (Lin et al. 2005, Tan et al. 2008).