Nitrotyrosine mimics phosphotyrosine binding to the SH2 domain of the src family tyrosine kinase lyn

The nitration of tyrosine residues in protein occurs through the action of reactive oxygen and nitrogen species and is considered a marker of oxidativ e stress under pathological conditions. The most active nitrating species s o far identified is peroxynitrite, the product of the reaction between nitr ic oxide and superoxide anion. Previously, we have reported that in erythro cytes peroxynitrite irreversibly upregulates lyn, a tyrosine kinase of the src family. In this study we investigated the possible role of tyrosine nit ration in the mechanism of lyn activation. We found that tyrosine containin g peptides modelled either on the C-terminal tail of src kinases or corresp onding to the first 15 amino acids of human erythrocyte band 3 were able to activate lyn when the tyrosine was substituted with 3-nitrotyrosine. The a ctivity of nitrated peptides was shared with phosphorylated but not with un phosphorylated, chlorinated or scrambled peptides. Recombinant lyn sm homol ogy 2 (SH2) domain blocked the capacity of the band 3-derived nitrotyrosine peptide to activate lyn and we demonstrated that this peptide specifically binds the SH2 domain of lyn. We propose that nitropeptides may activate sr c kinases through the displacement of the phosphotyrosine in the tail from its binding site in the SH2 domain. These observations suggest a new mechan ism of peroxynitrite-mediated signalling that may be correlated with the up regulation of tyrosine phosphorylation observed in several pathological con ditions. (C) 2001 Published by Elsevier Science B.V. on behalf of the Feder ation of European Biochemical Societies.