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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, natural killer (NK) cells, and in a subpopulation of CD4 T cells. CRTAM recognizes the ligand Nectin-like 2 (Necl2) through the IgV domain. However, the role of the IgC 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 demonstrate that the IgC domain forms a homodimer in solution via hydrophobic interactions. By surface plasmon resonance (SPR) analysis, we also demonstrate that CRTAM binds to Necl2 with an affinity of 2.16 nM. In conclusion, CRTAM's IgC is essential for a high-affinity interaction with Necl-2.

Class-I restricted T cell-associated molecule (CRTAM) is a member of the immunoglobulin superfamily, and it is closely related to nectin-like protein. CRTAM is expressed in activated CD8 T cells, NKT cells, NK cells and in a subpopulation CD4 T cells. In this study, we produce as recombinant proteins, the Ig-domains of CRTAM (IgV–IgC), the IgV, and the IgC. These proteins were successfully purified in the soluble fraction only if the stalk region was included. The recombinant CRTAM recognizes its ligand nectin-like 2 in a cell-free system. We also demonstrate that the IgC domain of CRTAM is recognized by the anti-hCRTAM monoclonal antibody C8 with a 0.62 nM affinity. In conclusion, the stalk region of CRTAM provides solubility for the expression of its Ig-domains as recombinant proteins. [ABSTRACT FROM AUTHOR]