Non-amyloid component of senile plaques found in Alzheimer disease. Could act as a regulator of SNCA aggregation process. Protects neurons from staurosporine and 6-hydroxy dopamine (6OHDA)-stimulated caspase activation in a p53/TP53-dependent manner. Contributes to restore the SNCA anti-apoptotic function abolished by 6OHDA. Not found in the Lewy bodies associated with Parkinson disease. Expressed predominantly in brain; concentrated in presynaptic nerve terminals. Phosphorylated. Phosphorylation by G-protein coupled receptor kinases (GRK) is more efficient than phosphorylation by CK1, CK2 and CaM-kinase II. Belongs to the synuclein family.