Structural insight into the specific interaction between murine SHPS-1/SIRP alpha and its ligand CD47Nakaishi, A., Hirose, M., Yoshimura, M., Oneyama, C., Saito, K., Kuki, N., Matsuda, M., Honma, N., Ohnishi, H., Matozaki, T., Okada, M., Nakagawa, A.
(2008) J.Mol.Biol. 375: 650-660
- PubMed: 18045614
- DOI: 10.1016/j.jmb.2007.10.085
- PubMed Abstract:
SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1 (SHPS-1 or SIRP alpha/BIT) is an immunoglobulin (Ig) superfamily transmembrane receptor and a member of the signal regulatory protein (SIRP) family involved in cell-cell intera ...
SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1 (SHPS-1 or SIRP alpha/BIT) is an immunoglobulin (Ig) superfamily transmembrane receptor and a member of the signal regulatory protein (SIRP) family involved in cell-cell interaction. SHPS-1 binds to its ligand CD47 to relay an inhibitory signal for cellular responses, whereas SIRPbeta, an activating member of the same family, does not bind to CD47 despite sharing a highly homologous ligand-binding domain with SHPS-1. To address the molecular basis for specific CD47 recognition by SHPS-1, we present the crystal structure of the ligand-binding domain of murine SHPS-1 (mSHPS-1). Folding topology revealed that mSHPS-1 adopts an I2-set Ig fold, but its overall structure resembles IgV domains of antigen receptors, although it has an extended loop structure (C'E loop), which forms a dimer interface in the crystal. Site-directed mutagenesis studies of mSHPS-1 identified critical residues for CD47 binding including sites in the C'E loop and regions corresponding to complementarity-determining regions of antigen receptors. The structural and functional features of mSHPS-1 are consistent with the human SHPS-1 structure except that human SHPS-1 has an additional beta-strand D. These results suggest that the variable complementarity-determining region-like loop structures in the binding surface of SHPS-1 are generally required for ligand recognition in a manner similar to that of antigen receptors, which may explain the diverse ligand-binding specificities of SIRP family receptors.
Laboratory of Supramolecular Crystallography, Research Center for Structural and Functional Proteomics, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan.