Structural insight into the specific interaction between murine SHPS-1/SIRP alpha and its ligand CD47.
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.
Aki
A
Nakaishi
Mayumi
M
Hirose
Masato
M
Yoshimura
Chitose
C
Oneyama
Kazunobu
K
Saito
Nobuharu
N
Kuki
Makoto
M
Matsuda
Nakayuki
N
Honma
Hiroshi
H
Ohnishi
Takashi
T
Matozaki
Masato
M
Okada
Atsushi
A
Nakagawa
D000409:Alanine / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D051928:CD47 Antigen / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D002448:Cell Adhesion; D006224:Cricetinae; D003412:Cricetulus; D018360:Crystallography, X-Ray; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D005822:Genetic Vectors; D006860:Hydrogen Bonding; D008024:Ligands; D008239:Lysine / Q000378:metabolism; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D008979:Moloney murine leukemia virus / Q000502:physiology; D010649:Phenylalanine / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000378:metabolism; D011971:Receptors, Immunologic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance; D014162:Transfection
D051928:CD47 Antigen; D004220:Disulfides; D008024:Ligands; C501922:Sirpa protein, mouse; D011948:Receptors, Antigen, T-Cell; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; C510031:SHPS-1-Fc fusion protein; D010649:Phenylalanine; D008239:Lysine; D000409:Alanine