Molecular Basis for a Direct Interaction between the Syk Protein-tyrosine Kinase and Phosphoinositide 3-Kinase

• Published in: The Journal of biological chemistry 2005-01, Vol.280 (2), p.1543-1551
• Main Authors: Moon, Kyung D., Post, Carol B., Durden, Donald L., Zhou, Qing, De, Pradip, Harrison, Marietta L., Geahlen, Robert L.
• Format: Article
• Language: English
• Subjects: Animals; Antigens, CD - genetics; Antigens, CD - metabolism; Binding Sites; Catalysis; COS Cells; Enzyme Precursors - chemistry; Enzyme Precursors - genetics; Enzyme Precursors - metabolism; Erythrocytes - immunology; Humans; Intracellular Signaling Peptides and Proteins; Mice; Models, Molecular; Molecular Weight; Phagocytosis; Phosphatidylinositol 3-Kinases - chemistry; Phosphatidylinositol 3-Kinases - genetics; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Phosphotyrosine - metabolism; Protein Binding; Protein Structure, Tertiary; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - metabolism; Protein-Tyrosine Kinases - chemistry; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - metabolism; Receptors, IgG - genetics; Receptors, IgG - metabolism; Sheep; src Homology Domains; Syk Kinase; Two-Hybrid System Techniques; ZAP-70 Protein-Tyrosine Kinase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M407805200

After engagement of the B cell receptor for antigen, the Syk protein-tyrosine kinase becomes phosphorylated on multiple tyrosines, some of which serve as docking sites for downstream effectors with SH2 or other phosphotyrosine binding domains. The most frequently identified binding partner for catalytically active Syk identified in a yeast two-hybrid screen was the p85 regulatory subunit of phosphoinositide 3-kinase. The C-terminal SH2 domain of p85 was sufficient for mediating an interaction with tyrosine-phosphorylated Syk. Interestingly, this domain interacted with Syk at phosphotyrosine 317, a site phosphorylated in trans by the Src family kinase, Lyn, and identified previously as a binding site for c-Cbl. This site interacted preferentially with the p85 C-terminal SH2 domain compared with the c-Cbl tyrosine kinase binding domain. Molecular modeling studies showed a good fit between the p85 SH2 domain and a peptide containing phosphotyrosine 317. Tyr-317 was found to be essential for Syk to support phagocytosis mediated by FcγRIIA receptors expressed in a heterologous system. These studies establish a new type of p85 binding site that can exist on proteins that serve as substrates for Src family kinases and provide a molecular explanation for observations on direct interactions between Syk and phosphoinositide 3-kinase.