NMR structure of phospho-tyrosine signaling complexes

A structural basis for activation and substrate specificity of src tyrosine kinases, and regulation of protein-protein association by tyrosine phospho rylation is described. Lyn, a src-family tyrosine kinase, recognizes and ph osphorylates the immunoreceptor tyrosine-based activation motif, ITAM, a cr itical component in transmembrane signal transduction in hemopoietic cells. The structure of an ITAM peptide substrate bound to an active form of Lyn tyrosine kinase was determined by high-resolution NMR, and a model of the c omplex was generated using the crystallographic structure of Lck, a closely related Src-family kinase. The results provide a rationale for the conserv ed ITAM residues and specificity of Lyn, and suggest that substrate plays a role in stabilizing the kinase conformation optimal for catalysis. It is o ur hope that the Lck-ITAM peptide model complex will be useful in aiding st ructure-based drug design efforts that target substrate binding determinant s in the design. Concerning the regulation of protein-protein association, we report on a complex between erythrocyte band 3 and two glycolytic enzyme s, aldolase and glyceraldehyde-3-phosphate dehydrogenase. The formation of this complex is negatively regulated by tyrosine phosphorylation of band 3 by p72syk tyrosine kinase. In red blood cells, this association results in a decrease in glycolysis due to competitive inhibition of the glycolytic en zymes. The structure of band 3 recognized by the glycolytic enzymes was det ermined by solution NMR, and found to be a loop structure with tyrosine cen trally positioned and excluded from intermolecular contact. This phosphoryl ation sensitive interaction, or PSI, loop may be the basis of a general mec hanism for negative regulation through tyrosine phosphorylation. (C) 1999 J ohn Wiley & Sons, Inc.