Effects of Halogenation on Tyrosine Phosphorylation and Peptide Binding to the Src Homology 2 Domain of Lymphocyte-Specific Protein Tyrosine Kinase

Phosphorylation of tyrosine residues by protein tyrosine kinases (PTK) andphosphotyrosine/Src homology 2 (SH2) domain interactions are crucial not only for signal transduction but also for regulation of PTK activity. Tyrosine residues alsoreceive nitration and halogenation under oxidative conditions. It has been reported that nitration of tyrosine residue caused peptides to be a poor substrate for PTK and that nitrotyrosine residues could bind to SH2 domains as a phosphotyrosine mimic to activate Src family kinase. However, the effect of halogenation on tyrosinephosphorylation or SH2 domain binding is not well understood. We examined thephosphorylation of model peptides containing 3-halotyrosine or 3-nitrotyrosine usingtypical receptor and nonreceptor tyrosine kinase (EGFR and Lck, respectively). TheEGFR- and Lck-mediated phosphorylation was markedly inhibited by tyrosinehalogenation. Iodination showed the strongest inhibition of the phosphorylation among four types of halogenation, and its inhibitory effect was stronger than that of nitration. We also examined the effect of iodination and nitration of tyrosine residues on binding to the SH2 domain of Lck, using a model peptide containing thephosphoTyr-Glu-Glu-Ile motif, which has a high affinity for the SH2 domain. Therelative affinities of the modified peptides whose phosphotyrosine was substituted with unphosphorylated tyrosine, 3-nitrotyrosine, and 3-iodotyrosine, and of the model peptide were 0.024, 0.26, 1, and 16, respectively. These results suggest that tyrosine iodination may have an effect on the phosphorylation or binding to the SH2 domain similar to nitration. Tyrosine iodination possibly modulates signal transduction, with the potential impairment of cell function