Crystal structure of SAP/FynSH3/SLAM ternary complex
[SH21A_HUMAN] Defects in SH2D1A are a cause of lymphoproliferative syndrome X-linked type 1 (XLP1) [MIM:308240]; also known as X-linked lymphoproliferative disease (XLPD) or Duncan disease. XLP is a rare immunodeficiency characterized by extreme susceptibility to infection with Epstein-Barr virus (EBV). Symptoms include severe or fatal mononucleosis, acquired hypogammaglobulinemia, pancytopenia and malignant lymphoma.         
[SH21A_HUMAN] Inhibitor of the SLAM self-association. Acts by blocking recruitment of the SH2-domain-containing signal-transduction molecule SHP-2 to a docking site in the SLAM cytoplasmic region. Mediates interaction between FYN and SLAMF1. May also regulate the activity of the neurotrophin receptors NTRK1, NTRK2 and NTRK3. [FYN_HUMAN] Non-receptor tyrosine-protein kinase that plays a role in many biological processes including regulation of cell growth and survival, cell adhesion, integrin-mediated signaling, cytoskeletal remodeling, cell motility, immune response and axon guidance. Inactive FYN is phosphorylated on its C-terminal tail within the catalytic domain. Following activation by PKA, the protein subsequently associates with PTK2/FAK1, allowing PTK2/FAK1 phosphorylation, activation and targeting to focal adhesions. Involved in the regulation of cell adhesion and motility through phosphorylation of CTNNB1 (beta-catenin) and CTNND1 (delta-catenin). Regulates cytoskeletal remodeling by phosphorylating several proteins including the actin regulator WAS and the microtubule-associated proteins MAP2 and MAPT. Promotes cell survival by phosphorylating AGAP2/PIKE-A and preventing its apoptotic cleavage. Participates in signal transduction pathways that regulate the integrity of the glomerular slit diaphragm (an essential part of the glomerular filter of the kidney) by phosphorylating several slit diaphragm components including NPHS1, KIRREL and TRPC6. Plays a role in neural processes by phosphorylating DPYSL2, a multifunctional adapter protein within the central nervous system, ARHGAP32, a regulator for Rho family GTPases implicated in various neural functions, and SNCA, a small pre-synaptic protein. Participates in the downstream signaling pathways that lead to T-cell differentiation and proliferation following T-cell receptor (TCR) stimulation. Also participates in negative feedback regulation of TCR signaling through phosphorylation of PAG1, thereby promoting interaction between PAG1 and CSK and recruitment of CSK to lipid rafts. CSK maintains LCK and FYN in an inactive form. Promotes CD28-induced phosphorylation of VAV1.                   [SLAF1_HUMAN] High-affinity self-ligand important in bidirectional T-cell to B-cell stimulation. SLAM-induced signal-transduction events in T-lymphocytes are different from those in B-cells. Two modes of SLAM signaling are likely to exist: one in which the inhibitor SH2D1A acts as a negative regulator and another in which protein-tyrosine phosphatase 2C (PTPN11)-dependent signal transduction operates.
Publication Abstract from PubMed
SAP (SLAM-associated protein) is a small lymphocyte-specific signalling molecule that is defective or absent in patients with X-linked lymphoproliferative syndrome (XLP). Consistent with its single src homology 2 (SH2) domain architecture and unusually high affinity for SLAM (also called CD150), SAP has been suggested to function by blocking binding of SHP-2 or other SH2-containing signalling proteins to SLAM receptors. Additionally, SAP has recently been shown to be required for recruitment and activation of the Src-family kinase FynT after SLAM ligation. This signalling 'adaptor' function has been difficult to conceptualize, because unlike typical SH2-adaptor proteins, SAP contains only a single SH2 domain and lacks other recognized protein interaction domains or motifs. Here, we show that the SAP SH2 domain binds to the SH3 domain of FynT and directly couples FynT to SLAM. The crystal structure of a ternary SLAM-SAP-Fyn-SH3 complex reveals that SAP binds the FynT SH3 domain through a surface-surface interaction that does not involve canonical SH3 or SH2 binding interactions. The observed mode of binding to the Fyn-SH3 domain is expected to preclude the auto-inhibited conformation of Fyn, thereby promoting activation of the kinase after recruitment. These findings broaden our understanding of the functional repertoire of SH3 and SH2 domains.
SAP couples Fyn to SLAM immune receptors.,Chan B, Lanyi A, Song HK, Griesbach J, Simarro-Grande M, Poy F, Howie D, Sumegi J, Terhorst C, Eck MJ Nat Cell Biol. 2003 Feb;5(2):155-60. PMID:12545174
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.