title: Structural characterization of a novel Cbl phosphotyrosine recognition motif in the APS family of adapter proteins.
abstract: The Cbl adapter proteins typically function to down-regulate activated protein tyrosine kinases and other signaling proteins by coupling them to the ubiquitination machinery for degradation by the proteasome. Cbl proteins bind to specific tyrosine-phosphorylated sequences in target proteins via the tyrosine kinase-binding (TKB) domain, which comprises a four-helix bundle, an EF-hand calcium-binding domain, and a non-conventional Src homology-2 domain. The previously derived consensus sequence for phosphotyrosine recognition by the Cbl TKB domain is NXpY(S/T)XXP (X denotes lesser residue preference), wherein specificity is conferred primarily by residues C-terminal to the phosphotyrosine. Cbl is recruited to and phosphorylated by the insulin receptor in adipose cells through the adapter protein APS. APS is phosphorylated by the insulin receptor on a C-terminal tyrosine residue, which then serves as a binding site for the Cbl TKB domain. Using x-ray crystallography, site-directed mutagenesis, and calorimetric studies, we have characterized the interaction between the Cbl TKB domain and the Cbl recruitment site in APS, which contains a sequence motif, RA(V/I)XNQpY(S/T), that is conserved in the related adapter proteins SH2-B and Lnk. These studies reveal a novel mode of phosphopeptide interaction with the Cbl TKB domain, in which N-terminal residues distal to the phosphotyrosine directly contact residues of the four-helix bundle of the TKB domain.
authors.affiliation: Structural Biology Program, Skirball Institute of Biomolecular Medicine and Department of Pharmacology, New York University School of Medicine, New York, New York 10016, USA.
authors.forename: Junjie
authors.initials: J
authors.lastname: Hu
authors.forename: Stevan R
authors.initials: SR
authors.lastname: Hubbard
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000737:chemistry* / Q000502:physiology; D000273:Adipose Tissue / Q000166:cytology; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002118:Calcium / Q000737:chemistry; D002151:Calorimetry; D006224:Cricetinae; D018360:Crystallography, X-Ray; D004583:Electrons; D015151:Immunoblotting; D047468:Immunoprecipitation; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D013816:Thermodynamics; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; C107249:SH2B2 protein, human; D019000:Phosphotyrosine; D014443:Tyrosine; D002118:Calcium