The mapping of the Lyn kinase binding site of the common beta subunit of IL-3/granulocyte-macrophage colony-stimulating factor/IL-5 receptor

It has been shown that a membrane-proximal region within common beta (beta c) receptor of IL-3/granulocyte-macrophage CSF/IL-5 (amino acids 450-517) i s important for Lyn binding. We have shown previously that Lyn kinase is ph ysically associated with the IL-5R beta c submit in unstimulated cells. The result suggests that this association involves binding modules that are no t activation or phosphorylation dependent, The objective of this study was to map the exact Lyn binding site on beta c. Using overlapping and/or seque ntial peptides derived from beta c 350-517, we narrowed down the Lyn bindin g site to nine amino acid residues, beta c 457-465, The P-->A mutation in t his region abrogated the binding to Lyn, indicating a critical role of prol ine residues. We created a cell-permeable Lyn-binding peptide by N-stearati on, This cell-permeable peptide blocked the association of Lyn, but not Jak 2 with beta c in situ. We also investigated the beta c binding site of Lyn kinase, Our results suggest that the N-terminal unique domain of Lyn kinase is important for binding to pc receptor. To our knowledge, this is the fir st molecular identification of the Lyn binding site of beta c receptor. Thi s finding may help develop specific inhibitors of Lyn-coupled signaling pat hways.