ZAG (zinc-a2-glycoprotein; also ZA2G) is a 40kD, secreted member of the MHC class I family of proteins. It is produced by adipocytes and various epithelial cells that generate exocrine-type secretions. ZAG is reported to stimulate lipid breakdown and thus may play a role in lipid homeostasis. Mature human ZAG is 278 amino acids (aa) in length. It contains one MHC class I antigen region (aa 26-201) and a C2-type Ig-like domain (aa 207-292). Two alternate splice forms exist; one shows a 66 aa substitution for the C-terminal 30 aa, and a second shows a nine Lys substitution for aa 151-298. Mature human ZAG is 60% aa identical to mouse ZAG.