Recruits the lipid transfer protein VPS13A from lipid droplets to the endoplasmic reticulum (ER) membrane. Heterodimer with Kell; disulfide-linked (PubMed:9593744). Interacts with VPS13A (PubMed:32845802, PubMed:31086825). High levels in skeletal muscle, heart, brain, and pancreas; low levels in placenta, lung, liver, and kidney. Not glycosylated. XK is responsible for the Kx blood group system. The disease is caused by variants affecting the gene represented in this entry. Belongs to the XK family.