Required for Ca(2+) flux in immune cells and plays a role in T-cell proliferation and in T-cell and neutrophil migration (By similarity). 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 (By similarity). Together with ZDHHC6, required for palmitoylation of ITPR1 in immune cells, leading to regulate ITPR1 stability and function. Plays a role in protection of cells from ER stress-induced apoptosis. Protects cells from oxidative stress when overexpressed in cardiomyocytes (By similarity). Interacts with DERL1, DERL2, DERL3 and SELENOS. The SELENOK-SELENOS complex interacts with VCP. Interacts with ZDHHC6. Probably mainly localized in the ER. 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 (By similarity). 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. Belongs to the selenoprotein K family. Truncated C-terminus.