A "three-pronged" binding mechanism for the SAP/SH2D1A SH2 domain: structural basis and relevance to the XLP syndrome.
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.
Hwang
Peter M
PM
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Li
Chengjun
C
Morra
Massimo
M
Lillywhite
Jennifer
J
Muhandiram
D Ranjith
DR
Gertler
Frank
F
Terhorst
Cox
C
Kay
Lewis E
LE
Pawson
Tony
T
Forman-Kay
Julie D
JD
Li
Shun-Cheng
SC
D015703:Antigens, CD; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D016384:Consensus Sequence / Q000235:genetics; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008232:Lymphoproliferative Disorders / Q000209:etiology / Q000235:genetics*; D009154:Mutation; D010449:Peptide Mapping; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D011956:Receptors, Cell Surface; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains
D015703:Antigens, CD; D002352:Carrier Proteins; D006023:Glycoproteins; D007136:Immunoglobulins; D047908:Intracellular Signaling Peptides and Proteins; D011956:Receptors, Cell Surface; C114953:SH2D1A protein, human; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1; D014443:Tyrosine