ABSTRACT
Transforming growth factor-beta (TGF-beta)-activated kinase 1 (TAK1) is a member of the MAPKKK family of protein kinases, and is involved in intracellular signalling pathways stimulated by transforming growth factor beta, interleukin-1 and tumour necrosis factor-alpha. TAK1 is known to rely upon an additional protein, TAK1-binding protein 1 (TAB1), for complete activation. However, the molecular basis for this activation has yet to be elucidated. We have solved the crystal structure of a novel TAK1 chimeric protein and these data give insight into how TAK1 is activated by TAB1. Our results reveal a novel binding pocket on the TAK1 kinase domain whose shape complements that of a unique alpha-helix in the TAK1 binding domain of TAB1, providing the basis for an intimate hydrophobic association between the protein activator and its target.
Subject(s)
Adaptor Proteins, Signal Transducing/chemistry , Adaptor Proteins, Signal Transducing/metabolism , MAP Kinase Kinase Kinases/chemistry , MAP Kinase Kinase Kinases/metabolism , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/isolation & purification , Adenosine/metabolism , Amino Acid Sequence , Baculoviridae/genetics , Binding Sites , Crystallography, X-Ray , Enzyme Activation , Humans , Hydrophobic and Hydrophilic Interactions , Kinetics , Mass Spectrometry , Models, Molecular , Molecular Sequence Data , Protein Binding , Protein Structure, Secondary , Protein Structure, Tertiary , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , Sequence Homology, Amino Acid , Substrate SpecificityABSTRACT
Interleukin-2 tyrosine kinase, Itk, is an important member of the Tec family of non-receptor tyrosine kinases that play a central role in signaling through antigen receptors such as the T-cell receptor, B-cell receptor, and Fcepsilon. Selective inhibition of Itk may be an important way of modulating many diseases involving heightened or inappropriate activation of the immune system. In addition to an unliganded nonphophorylated Itk catalytic kinase domain, we determined the crystal structures of the phosphorylated and nonphosphorylated kinase domain bound to staurosporine, a potent broad-spectrum kinase inhibitor. These structures are useful for the design of novel, highly potent and selective Itk inhibitors and provide insight into the influence of inhibitor binding and phosphorylation on the conformation of Itk.
