Mouse Clr-g, a Ligand for NK Cell Activation Receptor NKR-P1F: Crystal Structure and Biophysical Properties

Abstract

Interactions between C-type lectin-like NK cell receptors and their protein ligands form one of the key recognition mechanisms of the innate immune system that is involved in the elimination of cells that have been malignantly transformed, virally infected, or stressed by chemotherapy or other factors. We determined an x-ray structure for the extracellular domain of mouse C-type lectin related (Clr) protein g, a ligand for the activation receptor NKR-P1F. Clr-g forms dimers in the crystal structure resembling those of human CD69. This newly reported structure, together with the previously determined structure of mouse receptor NKR-P1A, allowed the modeling and calculations of electrostatic profiles for other closely related receptors and ligands. Despite the high similarity among Clr-g, Clr-b, and human CD69, these molecules have fundamentally different electrostatics, with distinct polarization of Clr-g. The electrostatic profile of NKR-P1F is complementary to that of Clr-g, which suggests a plausible interaction mechanism based on contacts between surface sites of opposite potential.

Structure of NKp65 bound to its keratinocyte ligand reveals basis for genetically linked recognition in natural killer gene complex

“…S5A). The mode of KACL dimerization resembles that of CD69 (34), Clrg (29), and certain Ly49s (22,23,37): Following superposition of the KACL and CD69 dimers through one of their subunits, the orientation of the other subunits differed by only an 8°rotation (23°for KACL superposed onto Clrg; 20°for KACL superposed onto Ly49L). As in the case of CD69 and other C-type lectin family dimers, the N termini of the KACL CTLDs point in the same direction (i.e., toward the cell membrane) (Fig.…”

“…In addition, we determined the structure of killer cell lectin-like receptor G1 (KLRG1) bound to E-cadherin, a non-MHC ligand that is down-regulated in metastatic tumors (27). By contrast, no structural information is available for any of the NKC-encoded receptor-ligand pairs identified to date (Nkrp1f-Clrg and Nkrp1d-Clrb in rodents and NKRP1A-LLT1, NKp80-AICL, and NKp65-KACL in humans), except for the structures of mouse Nkrp1a and Clrg in unbound form (28,29). To understand genetically linked recognition by C-type lectin-like receptors in the NKC at the atomic level, we determined the structure of NKp65 in complex with its keratinocyte ligand KACL.…”

Crystal structure of extracellular domain of human lectin‐like transcript 1 (LLT1), the ligand for natural killer receptor‐P1A

“…The structures of NKRP1 members were reported for human CD69, the mouse Clr-G proteins ([Protein Data Bank] PDB ID: 3RS1) [24] and mouse Nkrp1a (PDB IDs: 3M9Z and 3T3A) [25,26]. Their ectodomains adopt the C-type lectin fold, composed of two α-helices and two antiparallel β-sheets [27].…”

“…LLT1 and AICL bind their ligands, NKRP1A and NKp80, respectively, with low affinity (LLT1-NKRP1A: Kdß50 μM [23], AICL-NKp80: Kdß4 μM [14]), whereas NKp65 binds to KACL with significantly higher affinity (Kdß0.01 μM) [15]. Since these differences are strongly correlated with the recognition mechanisms, further structural studies at atomic resolution will be required for their clarification.The structures of NKRP1 members were reported for human CD69, the mouse Clr-G proteins ([Protein Data Bank] PDB ID: 3RS1) [24] and mouse Nkrp1a (PDB IDs: 3M9Z and 3T3A) [25,26]. Their ectodomains adopt the C-type lectin fold, composed of two α-helices and two antiparallel β-sheets [27].…”

Re-evaluation of the involvement of NK cells and C-type lectin-like NK receptors in modulation of immune responses by multivalent GlcNAc-terminated oligosaccharides

“…However, these results were not confirmed upon independent re-examination [7]. Moreover, it was demonstrated that NKR-P1 receptor family possess structural motifs optimized for the protein-protein, but not saccharide-protein interactions and protein ligands for some of them were identified [8][9][10][11][12][13][14][15].…”