title: CD45 specifically modulates binding of Lck to a phosphopeptide encompassing the negative regulatory tyrosine of Lck.
abstract: CD45 is a tyrosine phosphatase expressed in all hematopoietic cells which is important for signal transduction through the T cell antigen receptor (TCR). Studies using CD45-deficient cells have revealed that Lck, a tyrosine kinase thought to be essential for TCR signaling, is hyperphosphorylated on Y505 in the absence of CD45. This site of tyrosine phosphorylation negatively regulates the function of the Src family of kinases. Here we provide evidence that CD45 can modulate the binding of the Lck to an 11 amino acid tyrosine phosphorylated peptide containing the carboxy-terminus of Lck (lckP). Significantly, CD45 did not influence the binding of Fyn, PLC gamma 1, GAP and Vav to the same phosphopeptide. Lck protein which bound the peptide was dephosphorylated on Y505 and consisted of only 5-10% of the total cellular Lck. Interestingly, there was a marked increase in binding 15-30 min after CD4 or TCR cross-linking. Taken together, our data suggest that CD45 specifically modulates the conformation of Lck in a manner consistent with the intramolecular model of regulation of Src-like kinases.
authors.affiliation: Howard Hughes Medical Institute, Department of Medicine, University of California, San Francisco 94143.
authors.forename: M
authors.initials: M
authors.lastname: Sieh
authors.forename: J B
authors.initials: JB
authors.lastname: Bolen
authors.forename: A
authors.initials: A
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000502:physiology*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010748:Phosphopeptides / Q000378:metabolism; D011485:Protein Binding; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000302:isolation & purification / Q000378:metabolism; D014443:Tyrosine
chemical_list: D010455:Peptides; D010748:Phosphopeptides; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases; D010738:Type C Phospholipases