Efficient leukocyte Ig-like receptor signaling and crystal structure of disulfide-linked HLA-G dimer.
HLA-G is a nonclassical major histocompatibility complex class I (MHCI) molecule, which is expressed in trophoblasts and confers immunological tolerance in the maternal-fetal interface by binding to leukocyte Ig-like receptors (LILRs, also called as LIR/ILT/CD85) and CD8. HLA-G is expressed in disulfide-linked dimer form both in solution and at the cell surface. Interestingly, MHCI dimer formations have been involved in pathogenesis and T cell activation. The structure and receptor binding characteristics of MHCI dimers have never been evaluated. Here we performed binding studies showing that the HLA-G dimer exhibited higher overall affinity to LILRB1/2 than the monomer by significant avidity effects. Furthermore, the cell reporter assay demonstrated that the dimer formation remarkably enhanced the LILRB1-mediated signaling at the cellular level. We further determined the crystal structure of the wild-type dimer of HLA-G with the intermolecular Cys(42)-Cys(42) disulfide bond. This dimer structure showed the oblique configuration to expose two LILR/CD8-binding sites upward from the membrane easily accessible for receptors, providing plausible 1:2 (HLA-G dimer:receptors) complex models. These results indicated that the HLA-G dimer conferred increased avidity in a proper structural orientation to induce efficient LILR signaling, resulting in the dominant immunosuppressive effects. Moreover, structural and functional implications for other MHCI dimers observed in activated T cells and the pathogenic allele, HLA-B27, are discussed.
Shiroishi
Mitsunori
M
Division of Structural Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Kuroki
Kimiko
K
Ose
Toyoyuki
T
Rasubala
Linda
L
Shiratori
Ikuo
I
Arase
Hisashi
H
Tsumoto
Kouhei
K
Kumagai
Izumi
I
Kohda
Daisuke
D
Maenaka
Katsumi
K
D000483:Alleles; D000818:Animals; D001665:Binding Sites; D016827:CD8 Antigens / Q000737:chemistry; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D049452:Green Fluorescent Proteins / Q000737:chemistry; D006680:HLA Antigens / Q000737:chemistry*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000737:chemistry*; D007166:Immunosuppressive Agents / Q000737:chemistry; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D015398:Signal Transduction; D020349:Surface Plasmon Resonance; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors
D016827:CD8 Antigens; D004220:Disulfides; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D007166:Immunosuppressive Agents; C476771:LMIR1 protein, mouse; D010455:Peptides; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D003545:Cysteine