Required for Ca(2+) flux in immune cells and plays a role in T-cell proliferation and in T-cell and neutrophil migration (PubMed:21220695). Involved in endoplasmic reticulum-associated degradation (ERAD) of soluble glycosylated proteins (By similarity). Required for palmitoylation and cell surface expression of CD36 and involved in macrophage uptake of low-density lipoprotein and in foam cell formation (PubMed:23444136). Together with ZDHHC6, required for palmitoylation of ITPR1 in immune cells, leading to regulate ITPR1 stability and function (PubMed:25368151). Plays a role in protection of cells from ER stress-induced apoptosis (By similarity). Protects cells from oxidative stress when overexpressed in cardiomyocytes (By similarity). Interacts with DERL1, DERL2, DERL3 and SELENOS (PubMed:22016385). The SELENOK-SELENOS complex interacts with VCP (By similarity). Interacts with ZDHHC6 (PubMed:25368151). Probably mainly localized in the ER. High expression in spleen and intestine (at protein level). Expressed in a range of immune cells including T and B-cells and also in myeloid cells including macrophages, neutrophils and dendritic cells (at protein level). By increased dietary selenium. Expression is significantly decreased by a low selenium diet. Cleaved by CAPN2/m-calpain in resting macrophages but not in activated macrophages. Macrophage activation up-regulates expression of the calpain inhibitor CAST/calpastatin, resulting in inhibition of CAPN2 activity. Truncated SELENOK proteins produced by failed UGA/Sec decoding are ubiquitinated by the CRL2(KLHDC2) complex, which recognizes the diglycine (Gly-Gly) at the C-terminus of truncated SELENOK proteins. Normal growth, fertility and immune system development. Reduced receptor-mediated Ca(2+) flux in T-cells, neutrophils and macrophages. Reduced T-cell proliferation and reduced T-cell and neutrophil migration. Decreased viral clearance and increased mortality following infection with West Nile virus. Bone marrow-derived macrophages from knockout mice display decreased uptake of acetylated or oxidized low-density lipoprotein, reduced foam cell formation and decreased palmitoylation and cell surface expression of CD36. Belongs to the selenoprotein K family. Truncated C-terminus.