CDB20:0002853 NECTIN2 — TIGIT

ABSTRACT: 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. Although 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, whereas 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.

ABSTRACT: TIGIT (T cell immunoglobulin and ITIM domain) is an inhibitory receptor expressed on T and NK cells that interact with cell surface glycoprotein belonging to the nectin and nectin-like family of cell adhesion molecules, particularly nectin-2 and nectin-like 5 (PVR). Nectin-4 has been recently identified as a novel ligand for TIGIT and the interaction among them inhibits NK cell cytotoxicity. In this study, biophysical experiments were conducted to decipher the mechanism of this novel interaction, followed by structure-guided mutagenesis studies to map the nectin-4 binding interface on TIGIT. Using surface plasmon resonance, we deduced that TIGIT recognizes the membrane distal ectodomain of nectin-4 and the interaction is weaker than the well-characterized TIGIT: nectin-2 interaction. Deciphering the molecular basis of this newly identified interaction between TIGIT and nectin-4 will provide us important insight into the manipulation of this inhibitory signaling pathway, especially targeting cancer cells overexpressing nectin-4 that evade the immune surveillance of the body.