α-Synuclein is phosphorylated by members of the Src family of protein-tyrosine kinases

alpha -Synuclein (alpha -Syn) is implicated in the pathogenesis of Parkinson's Disease, genetically through missense mutations linked to early onset disease and pathologically through its presence in Lewy bodies. alpha -Syn is phosphorylated on serine residues; however, tyrosine phosphorylation of alpha -Syn has not been established (1, 2). A comparison of the protein sequence between Synuclein family members revealed that all four tyrosine residues of alpha -Syn are conserved in all orthologs and beta -Syn paralogs described to date, suggesting that these residues may be of functional importance (3). For this reason, experiments were performed to determine whether alpha -Syn could be phosphorylated on tyrosine residue(s) in human cells. Indeed, alpha -Syn is phosphorylated within 2 min of pervanadate treatment in alpha -Syn-transfected cells. Tyrosine phosphorylation occurs primarily on tyrosine 125 and was inhibited by PP2, a selective inhibitor of Src protein-tyrosine kinase (PTK) family members at concentrations consistent with inhibition of Src function (4). Finally, we demonstrate that alpha -Syn can be phosphorylated directly both in cotransfection experiments using c-Src and Fyn expression vectors and in in vitro kinase assays with purified kinases. These data suggest that alpha -Syn can be a target for phosphorylation by the Src family of PTKs.