title: Novel mode of ligand binding by the SH2 domain of the human XLP disease gene product SAP/SH2D1A.
abstract: BACKGROUND
  The Src homology 2 (SH2) domains of cytoplasmic signaling proteins generally bind phosphotyrosine (pTyr) sites in the context of carboxy-terminal residues. SAP (also known as SH2D1A or DSHP), the product of the gene that is mutated in human X-linked lymphoproliferative (XLP) disease, comprises almost exclusively a single SH2 domain, which may modulate T-cell signaling by engaging T-cell co-activators such as SLAM, thereby blocking binding of other signaling proteins that contain SH2 domains. The SAP-SLAM interaction can occur in a phosphorylation-independent manner.
  
  
  RESULTS
  To characterize the interaction between SAP and SLAM, we synthesized peptides corresponding to the SAP-binding site at residue Y281 in SLAM. Both phosphorylated and non-phosphorylated versions of an 11-residue SLAM peptide bound SAP, with dissociation constants of 150 nM and 330 nM, respectively. SLAM phosphopeptides that were truncated either at the amino or carboxyl terminus bound with high affinity to SAP, suggesting that the SAP SH2 domain recognizes both amino-terminal and carboxy-terminal sequences relative to the pTyr residue. These results were confirmed by nuclear magnetic resonance (NMR) studies on (15)N- and (13)C-labeled SAP complexed with three SLAM peptides: an amino-terminally truncated phosphopeptide, a carboxy-terminally truncated phosphopeptide and a non-phosphorylated Tyr-containing full-length peptide.
  
  
  CONCLUSIONS
  The SAP SH2 domain has a unique specificity. Not only does it bind peptides in a phosphorylation-independent manner, it also recognizes a pTyr residue either preceded by amino-terminal residues or followed by carboxy-terminal residues. We propose that the three 'prongs' of a peptide ligand (the amino and carboxyl termini and the pTyr) can engage the SAP SH2 domain, accounting for its unusual properties. These data point to the flexibility of modular protein-interaction domains.
authors.affiliation: Program in Molecular Biology and Cancer, Department of Molecular and Medical Genetics, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Canada.
authors.forename: S C
authors.initials: SC
authors.lastname: Li
authors.forename: G
authors.initials: G
authors.lastname: Gish
authors.forename: D
authors.initials: D
authors.lastname: Yang
authors.forename: A J
authors.initials: AJ
authors.lastname: Coffey
authors.forename: J D
authors.initials: JD
authors.lastname: Forman-Kay
authors.forename: I
authors.initials: I
authors.lastname: Ernberg
authors.forename: L E
authors.initials: LE
authors.lastname: Kay
authors.forename: T
authors.initials: T
authors.lastname: Pawson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000345:Affinity Labels / Q000032:analysis; D000595:Amino Acid Sequence / Q000235:genetics; D015703:Antigens, CD; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008232:Lymphoproliferative Disorders / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D019000:Phosphotyrosine / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D011956:Receptors, Cell Surface; D055765:Shc Signaling Adaptor Proteins; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000345:Affinity Labels; D015703:Antigens, CD; D002352:Carrier Proteins; D006023:Glycoproteins; D007136:Immunoglobulins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D011506:Proteins; D011956:Receptors, Cell Surface; C114953:SH2D1A protein, human; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1; D019000:Phosphotyrosine; D014443:Tyrosine