Recognition of nectin-2 by the natural killer cell receptor TIGIT [Immunology]

T cell immunoglobulin and ITIM domain (TIGIT) is an inhibitory receptor expressed on the surface of natural killer (NK) cells. TIGIT recognizes nectin and nectin-like adhesion molecules and thus plays a critical role in the innate immune response to malignant transformation. While the TIGIT nectin-like protein-5 (necl-5) interaction is well understood, how TIGIT engages nectin-2, a receptor that is broadly over-expressed in breast and ovarian cancer, remains unknown. Here, we show that TIGIT bound to the immunoglobulin domain of nectin-2 that is most distal from the membrane with an affinity of 6 μM, which was moderately lower than the affinity observed for the TIGIT-necl-5 interaction (3.2 μM). The TIGIT-nectin-2 binding disrupted pre-assembled nectin-2 oligomers, suggesting that receptor-ligand and ligand-ligand associations are mutually exclusive events. Indeed, the crystal structure of TIGIT bound to the first immunoglobulin domain of nectin-2 indicated that the receptor and ligand dock using the same molecular surface and a conserved ″lock and key″ binding motifs previously observed to mediate nectin-nectin homotypic interactions as well as TIGIT-necl-5 recognition. Using a mutagenesis approach, we dissected the energetic basis for the TIGIT-nectin-2 interaction and revealed that an ″aromatic key″ of nectin-2 is critical for this interaction, while variations in the lock were tolerated. Moreover, we found that the C-C′ loop of the ligand dictates the TIGIT binding hierarchy. Altogether, these findings broaden our understanding of nectin-nectin receptor interactions and have implications for better understanding the molecular basis for autoimmune disease and cancer.

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