Structural Insights into the Inhibitory Mechanism of an Antibody against B7-H6, a Stress-Induced Cellular Ligand for the Natural Killer Cell Receptor NKp30.
Antibodies have been shown to block signaling through cell surface receptors using several mechanisms. The two most common are binding to the ligand-binding site of the receptor and, conversely, binding to the receptor-binding site of the ligand. Here, we investigated the inhibitory mechanism of an antibody (17B1.3) against human B7-H6, a stress-induced cellular ligand for the natural killer (NK) cell receptor NKp30. Binding of this antibody to B7-H6, a transmembrane protein expressed on tumor and other stressed cells, but not on normal cells, prevents NK cell activation via NKp30. We determined the crystal structure of antibody 17B1.3 in complex with the ectodomain of B7-H6 to 2.5Å resolution. Surprisingly, 17B1.3 binds to a site on B7-H6 that is completely distinct from the binding site for NKp30, such that 17B1.3 does not block the NKp30-B7-H6 interaction. We then asked whether 17B1.3 prevents signaling by binding to a putative site for B7-H6 dimerization. However, structure-based mutations designed to disrupt potential B7-H6 dimerization through this site did not diminish NKp30-mediated cell activation. We conclude that the bulky 17B1.3 antibody most likely acts by sterically interfering with close cell-cell contacts at the NK cell-target cell interface that are required for NK cell activation. A similar inhibitory mechanism may apply to other antibodies, including therapeutic antibodies that block signaling through cell surface receptors whose ligands are also cell surface proteins.
University of Maryland Institute for Bioscience and Biotechnology Research, W.M. Keck Laboratory for Structural Biology, Rockville, MD 20850, USA; State Key Laboratory of Oral Diseases, West China School of Stomatology, Sichuan University, Sichuan 610041, People's Republic of China.
Xiaoping
X
Xu
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille University UM2, Inserm, U1104, CNRS UMR7280, Marseille 13288, France.
Emilie
E
Narni-Mancinelli
Dipartimento di Medicina Sperimentale, Università degli Studi di Genova, Genova 16132, Italy; Centro di Eccellenza per le Ricerche Biomediche, Università degli Studi di Genova, Genova 16132, Italy; Istituto Giannina Gaslini, Genova 16147, Italy.
Claudia
C
Cantoni
University of Maryland Institute for Bioscience and Biotechnology Research, W.M. Keck Laboratory for Structural Biology, Rockville, MD 20850, USA; Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
Yili
Y
Li
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille University UM2, Inserm, U1104, CNRS UMR7280, Marseille 13288, France.
Sophie
S
Guia
Innate Pharma S.A., Marseille 13009, France.
Laurent
L
Gauthier
State Key Laboratory of Oral Diseases, West China School of Stomatology, Sichuan University, Sichuan 610041, People's Republic of China.
Qianming
Q
Chen
Dipartimento di Medicina Sperimentale, Università degli Studi di Genova, Genova 16132, Italy; Centro di Eccellenza per le Ricerche Biomediche, Università degli Studi di Genova, Genova 16132, Italy.
Alessandro
A
Moretta
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille University UM2, Inserm, U1104, CNRS UMR7280, Marseille 13288, France; Immunologie, Hôpital de la Conception, Assistance Publique - Hôpitaux de Marseille, Aix-Marseille Université, Marseille 13005, France.
Frédéric
F
Vély
University of Maryland Institute for Bioscience and Biotechnology Research, W.M. Keck Laboratory for Structural Biology, Rockville, MD 20850, USA; Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA.
Edward
E
Eisenstein
University of Maryland Institute for Bioscience and Biotechnology Research, W.M. Keck Laboratory for Structural Biology, Rockville, MD 20850, USA; Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
Sneha
S
Rangarajan
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille University UM2, Inserm, U1104, CNRS UMR7280, Marseille 13288, France. Electronic address: vivier@ciml.univ-mrs.fr.
Eric
E
Vivier
University of Maryland Institute for Bioscience and Biotechnology Research, W.M. Keck Laboratory for Structural Biology, Rockville, MD 20850, USA; Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA. Electronic address: rmariuzz@umd.edu.
Roy A
RA
Mariuzza
D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism*; D060887:B7 Antigens / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D006801:Humans; D008958:Models, Molecular; D055628:Natural Cytotoxicity Triggering Receptor 3 / Q000378:metabolism*; D011487:Protein Conformation
D000911:Antibodies, Monoclonal; D060887:B7 Antigens; C431710:NCR3 protein, human; C542363:NCR3LG1 protein, human; D055628:Natural Cytotoxicity Triggering Receptor 3
NK cell activation; NK cell receptor; antibody; antibody–ligand complex; crystal structure