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  • The EMBO Journal (2002) 21, 314 - 323
  • doi:10.1093/emboj/21.3.314

A 'three-pronged' binding mechanism for the SAP/SH2D1A SH2 domain: structural basis and relevance to the XLP syndrome

Peter M. Hwang1, Chengjun Li2, Massimo Morra3, Jennifer Lillywhite2, D.Ranjith Muhandiram1,4, Frank Gertler5, Cox Terhorst3, Lewis E. Kay1,4,6, Tony Pawson4,7, Julie D. Forman-Kay1,8 and Shun-Cheng Li2

  1. Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
  2. Department of Biochemistry, Faculty of Medicine and Dentistry, University of Western Ontario, London, Ontario N6A 5C1, Canada
  3. Division of Immunology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215 USA
  4. Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
  5. Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
  6. Department of Chemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
  7. Samuel Lunenfeld Research Institute, Mt Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
  8. Program in Structural Biology and Biochemistry, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada

Correspondence to:

Shun-Cheng Li, E-mail: sli@uwo.ca

Received 3 September 2001; Accepted 5 December 2001; Revised 14 November 2001

The SH2 domain protein SAP/SH2D1A, encoded by the X-linked lymphoproliferative (XLP) syndrome gene, associates with the hematopoietic cell surface receptor SLAM in a phosphorylation-independent manner. By screening a repertoire of synthetic peptides, the specificity of SAP/SH2D1A has been mapped and a consensus sequence motif for binding identified, T/S-x-x-x-x-V/I, where x represents any amino acid. Remarkably, this motif contains neither a Tyr nor a pTyr residue, a hallmark of conventional SH2 domain–ligand interactions. The structures of the protein, determined by NMR, in complex with two distinct peptides provide direct evidence in support of a 'three-pronged' binding mechanism for the SAP/SH2D1A SH2 domain in contrast to the 'two-pronged' binding for conventional SH2 domains. Differences in the structures of the two complexes suggest considerable flexibility in the SH2 domain, as further confirmed and characterized by hydrogen exchange studies. The structures also explain binding defects observed in disease-causing SAP/SH2D1A mutants and suggest that phosphorylation-independent interactions mediated by SAP/SH2D1A likely play an important role in the pathogenesis of XLP.

  • Keywords:

    • immunodeficiency,
    • SAP,
    • SH2 domain,
    • SH2D1A,
    • XLP