Structural nature of the interaction between T lymphocyte surface molecule CD4 and the intracellular protein tyrosine kinase Ick

The strong non-covalent interactions between T lymphocyte surface CD4 or CD8 molecules and the intracellular membrane-associated protein tyrosine kinase lck are likely to mediate the role of CD4 and CD8 molecules in the immune response. The delineation of the structural nature of the CD4/lck and CD8/lck complexes is important for the understanding of the biochemical and functional significance of the interactions. Complementary charged regions in the C-terminal intracytoplasmic portions of CD4 or CD8, and in the N-terminal region of protein tyrosine kinase lck were noted. Peptides spanning these regions, residues 417 to 429 of CD4 and 10 to 22 of lck, were found to specifically dissociate these two molecules in CD4/lck complexes. A structural model of the interaction that accounts for its high stability is proposed.