About ULBP / UL16 binding protein:
UL16 binding protein (ULBP) is a glycoprotein found on the cell surface encoded by a gene in chromosome 6. ULBP is one of the MHC classes I molecules through its gene maps from the outside locus on the MHC. The UL16 binding protein is an unusual member of the MHC class I molecules without the alpha-3 and transmembrane domains. The ULBP binds and activates the KLRK1 receptor to mediate cell cytotoxicity.
The structure of ULBP is slightly different from those of the MHC class I molecules. The ULBP structure lacks the alpha-3 domain and the transmembrane segment. Therefore, its general structure is made up of the alpha-1 and alpha-2 domains connected to the cell membrane through the GPI anchor.
UL16 binding protein Interaction
The UL16 binding protein interacts with KLRK1/NKG2D. However, it is not linked to any beta-2-microglobulin. Additionally, it interacts with viral glycoprotein (UL16) to offer CMV an immune evasion mechanism. This interaction leads to the retention of ULBP1 in the endoplasmic reticulum.
NK cells are among the vital constituents of the innate immune system responsible for recognizing neoplastic cells. Various studies show that UL16 binding proteins are essential in activating NK cells and binding human NK cells to stimulate NK cytotoxicity.
Additionally, UL16 binding proteins also enhance the production of cytokines and chemokines macrophage-inflammatory proteins. The costimulation further aids the process with IL-12, which has a superadditive effect in producing various protein forms.
UL16 binding proteins alone can activate various signaling pathways and enhance the production of modest cytokines. However, they can also link with interleukin-12 to induce interferon-gamma production in the NK cells.