Signaling by the human C-type lectin-like receptor, natural killer (NK) cell inhibitory receptor NKR-P1, has a critical role in many immune-related diseases and cancer. C-type lectin-like receptors have weak affinities to their ligands; therefore, setting up a comprehensive model of NKR-P1-LLT1 interactions that considers the natural state of the receptor on the cell surface is necessary to understand its functions. Here we report the crystal structures of the NKR-P1 and NKR-P1:LLT1 complexes, which provides evidence that NKR-P1 forms homodimers in an unexpected arrangement to enable LLT1 binding in two modes, bridging two LLT1 molecules. These interaction clusters are suggestive of an inhibitory immune synapse. By observing the formation of these clusters in solution using SEC-SAXS analysis, by dSTORM super-resolution microscopy on the cell surface, and by following their role in receptor signaling with freshly isolated NK cells, we show that only the ligation of both LLT1 binding interfaces leads to effective NKR-P1 inhibitory signaling. In summary, our findings collectively support a model of NKR-P1:LLT1 clustering, which allows the interacting proteins to overcome weak ligand-receptor affinity and to trigger signal transduction upon cellular contact in the immune synapse.

• MeSH
• Antigens, Surface MeSH
• Killer Cells, Natural * MeSH
• X-Ray Diffraction MeSH
• NK Cell Lectin-Like Receptor Subfamily B MeSH
• Lectins, C-Type MeSH
• Humans MeSH
• Ligands MeSH
• Scattering, Small Angle MeSH
• Receptors, Cell Surface * MeSH
• Cluster Analysis MeSH
• Synapses MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens, Surface MeSH
• NK Cell Lectin-Like Receptor Subfamily B MeSH
• Lectins, C-Type MeSH
• Ligands MeSH
• Receptors, Cell Surface * MeSH

Targeted cancer immunotherapy is a promising tool for restoring immune surveillance and eradicating cancer cells. Hydrophilic polymers modified with coiled coil peptide tags can be used as universal carriers designed for cell-specific delivery of such biologically active proteins. Here, we describe the preparation of pHPMA-based copolymer conjugated with immunologically active protein B7-H6 via complementary coiled coil VAALEKE (peptide E) and VAALKEK (peptide K) sequences. Receptor B7-H6 was described as a binding partner of NKp30, and its expression has been proven for various tumor cell lines. The binding of B7-H6 to NKp30 activates NK cells and results in Fas ligand or granzyme-mediated apoptosis of target tumor cells. In this work, we optimized the expression of coiled coil tagged B7-H6, its ability to bind activating receptor NKp30 has been confirmed by isothermal titration calorimetry, and the binding stoichiometry of prepared chimeric biopolymer has been characterized by analytical ultracentrifugation. Furthermore, this coiled coil B7-H6-loaded polymer conjugate activates NK cells in vitro and, in combination with coiled coil scFv, enables their targeting towards a model tumor cell line. Prepared chimeric biopolymer represents a promising precursor for targeted cancer immunotherapy by activating the cytotoxic activity of natural killer cells.

• Keywords
• B7-H6, HPMA polymer, NK cell, NKp30, coiled coil, immunotherapy,
• Publication type
• Journal Article MeSH

Working at the border between innate and adaptive immunity, natural killer (NK) cells play a key role in the immune system by protecting healthy cells and by eliminating malignantly transformed, stressed or virally infected cells. NK cell recognition of a target cell is mediated by a receptor "zipper" consisting of various activating and inhibitory receptors, including C-type lectin-like receptors. Among this major group of receptors, two of the largest rodent receptor families are the NKR-P1 and the Clr receptor families. Although these families have been shown to encode receptor-ligand pairs involved in MHC-independent self-nonself discrimination and are a target for immune evasion by tumour cells and viruses, structural mechanisms of their mutual recognition remain less well characterized. Therefore, we developed a non-viral eukaryotic expression system based on transient transfection of suspension-adapted human embryonic kidney 293 cells to produce soluble native disulphide dimers of NK cell C-type lectin-like receptor ectodomains. The expression system was optimized using green fluorescent protein and secreted alkaline phosphatase, easily quantifiable markers of recombinant protein production. We describe an application of this approach to the recombinant protein production and characterization of native rat NKR-P1B and Clr-11 proteins suitable for further structural and functional studies.

• MeSH
• HEK293 Cells MeSH
• Rats MeSH
• NK Cell Lectin-Like Receptor Subfamily B chemistry   genetics   metabolism   MeSH
• Humans MeSH
• Protein Multimerization MeSH
• Calcitonin Receptor-Like Protein chemistry   genetics   metabolism   MeSH
• Protein Domains MeSH
• Protein Engineering methods   MeSH
• Recombinant Proteins chemistry   genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Calcrl protein, rat MeSH Browser
• NK Cell Lectin-Like Receptor Subfamily B MeSH
• Calcitonin Receptor-Like Protein MeSH
• Recombinant Proteins MeSH

Human LLT1 is a C-type lectin-like ligand of NKR-P1 (CD161, gene KLRB1), a C-type lectin-like receptor of natural killer cells. Using X-ray diffraction, the first experimental structures of human LLT1 were determined. Four structures of LLT1 under various conditions were determined: monomeric, dimeric deglycosylated after the first N-acetylglucosamine unit in two forms and hexameric with homogeneous GlcNAc2Man5 glycosylation. The dimeric form follows the classical dimerization mode of human CD69. The monomeric form keeps the same fold with the exception of the position of an outer part of the long loop region. The hexamer of glycosylated LLT1 consists of three classical dimers. The hexameric packing may indicate a possible mode of interaction of C-type lectin-like proteins in the glycosylated form.

• Keywords
• C-type lectin-like ligand, LLT1,
• MeSH
• Glycosylation MeSH
• Protein Structure, Quaternary MeSH
• NK Cell Lectin-Like Receptor Subfamily B chemistry   genetics   metabolism   MeSH
• Lectins, C-Type chemistry   genetics   metabolism   MeSH
• Humans MeSH
• Protein Multimerization * MeSH
• Receptors, Cell Surface chemistry   genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• CLEC2D protein, human MeSH Browser
• KLRB1 protein, human MeSH Browser
• NK Cell Lectin-Like Receptor Subfamily B MeSH
• Lectins, C-Type MeSH
• Receptors, Cell Surface MeSH

The binding of monosaccharides and short peptides to lymphocyte receptors (human CD69 and rat NKR-P1A) was first reported in 1994 and then in a number of subsequent publications. Based on this observation, numerous potentially high-affinity saccharide ligands have been synthesized over the last two decades in order to utilize their potential in antitumor therapy. Due to significant inconsistencies in their reported binding properties, we decided to re-examine the interaction between multiple ligands and CD69 or NKR-P1A. Using NMR titration and isothermal titration calorimetry we were unable to detect the binding of the tested ligands such as N-acetyl-D-hexosamines and oligopeptides to both receptors, which contradicts the previous observations published in more than twenty papers over the last fifteen years.

• MeSH
• Antigens, CD metabolism   MeSH
• Antigens, Differentiation, T-Lymphocyte metabolism   MeSH
• Rats MeSH
• Lectins, C-Type metabolism   MeSH
• Humans MeSH
• Oligopeptides chemical synthesis   pharmacology   MeSH
• Polysaccharides chemical synthesis   pharmacology   MeSH
• Receptors, Immunologic metabolism   MeSH
• Recombinant Proteins metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens, CD MeSH
• CD69 antigen MeSH Browser
• Antigens, Differentiation, T-Lymphocyte MeSH
• Klrb1a protein, rat MeSH Browser
• Lectins, C-Type MeSH
• Oligopeptides MeSH
• Polysaccharides MeSH
• Receptors, Immunologic MeSH
• Recombinant Proteins MeSH

The structure of the extracellular domain of human CD69 has been determined by single-crystal X-ray diffraction. The structure refined to 1.37 A resolution provides further details of the overall structure and the asymmetric interface between the monomers in the native dimer. The protein was crystallized using di[poly(ethylene glycol)] adipate, which also served as a cryoprotectant. This is the first report of a crystal structure determined using crystals grown with this polymer.

• MeSH
• Antigens, CD chemistry   MeSH
• Antigens, Differentiation, T-Lymphocyte chemistry   MeSH
• Protein Conformation MeSH
• Crystallography, X-Ray MeSH
• Lectins, C-Type chemistry   MeSH
• Humans MeSH
• Models, Molecular MeSH
• Polymers chemistry   MeSH
• Recombinant Proteins chemistry   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens, CD MeSH
• CD69 antigen MeSH Browser
• Antigens, Differentiation, T-Lymphocyte MeSH
• Lectins, C-Type MeSH
• Polymers MeSH
• Recombinant Proteins MeSH