Anti-ERVK-21 antibodies are used in the immunodetection of the protein endogenous retrovirus group K member 21, envelope. In humans, the canonical protein has a reported length of 698 amino acid residues and a mass of 79.2 kDa. Its subcellular localization is in the cell membrane. It is a member of the Beta type-B retroviral envelope protein family. Post-translational modifications have been described, including protein cleavage and glycosylation.