PALMITYLATION OF AN AMINO-TERMINAL CYSTEINE MOTIF OF PROTEIN-TYROSINEKINASES P56LCK AND P59FYN MEDIATES INTERACTION WITH GLYCOSYL-PHOSPHATIDYLINOSITOL-ANCHORED PROTEINS

Cross-linking of glycosyl-phosphatidylinositol (GPI)-anchored membrane proteins on T cells can trigger cell activation. We and others have s hown an association between GPI-anchored proteins and the protein tyro sine kinases (PTKs) p56lck and p59fyn, suggesting a pathway for signal ing through GPI-anchored proteins. Studies of decay-accelerating facto r (DAF) or CD59 in either the C32 cell line or the HeLa cell line tran sfected with PTK cDNA demonstrated that the GPI-anchored proteins asso ciated noncovalently with p56lck and p59fyn but not with p60src. Nonmy ristylated versions of p56lck and p59fyn also failed to associate with the GPI-anchored proteins. Mutational analysis of the PTK demonstrate d that the association with the GPI-anchored proteins mapped to the un ique amino-terminal domains of the PTK. A chimeric PTK consisting of t he 10 amino-terminal residues of p56lck or p59fyn replacing the corres ponding amino acids in p60scr was sufficient for association with DAF, but the converse constructs containing the first 10 amino acids of p6 0scr plus the remainder of p56lck or p59fyn did not associate with DAF . Mutation of cysteine to serine at positions 3 and 6 in p59fyn or pos itions 3 and 5 in p56lck abolished the association of these kinases wi th DAF. Mutation of serine to cysteine at positions 3 and 6 in p60scr conferred on p60scr the ability to associate with DAF. Direct labeling with [H-3]palmitate demonstrated palmitylation of this amino-terminal cysteine motif in p56lck. Thus, palmitylation of the amino-terminal c ysteine residue(s) together with myristylation of the amino-terminal g lycine residue defines important motifs for the association of PTKs wi th GPI-anchored proteins.