This 19 kDa glycoprotein binds the major histocompatibility (MHC) class I antigens in the endoplasmic reticulum (ER). The ER retention signal at the C-terminus of GP19K causes retention of the complex in the ER, preventing lysis of the cell by cytotoxic T lymphocytes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",