The constant domain of CRTAM is essential for high-affinity interaction with Nectin-like 2

CRTAM (Class-I MHC-restricted T cell-associated molecule) is a member of the Nectin-like family, composed of two extracellular domains, one constant domain (IgC), and another variable domain (IgV), expressed in activated CD8 T cells, epithelial cells, NK cells and in a subpopulation CD4 T cell. CRTAM recognizes the ligand Nectin-like 2 (Necl2) through the variable domain. However, the role of the constant domain during this ligand recognition has yet to be understood. In this study, we show the purification of soluble-folded Ig-domains of CRTAM, and we demonstrated that the constant domain forms a homodimer in solution via hydrophobic interactions. By SRP analysis, we also demonstrate that the full CRTAM binds to Necl2 with a 2.16 nM affinity. Additionally, transfected cells expressing the full length of CRTAM on the surface establish a better interaction with Necl2 than with the CRTAM-IgC domain expressed on the cell surface. In conclusion, the constant domain of CRTAM is essential for high-affinity interaction with Necl-2.