Ghrelin O-acyltransferase also known as membrane bound O-acyltransferase domain containing 4 is an enzyme that in humans is encoded by the MBOAT4 gene. It is homologous to other membrane-bound O-acyltransferases. It is a polytopic membrane protein what takes part in lipid signaling reactions. It is the only known enzyme that catalyzes the acylation of ghrelin through the transfer of n-octanoic acid to ghrelin Ser3. Ghrelin O-acyltransferase function is essential in regulation of appetite and the release of growth hormone. Ghrelin O-acyltransferase is a target for scientific research due to promising applications in the treatment of diabetes, eating disorders, and metabolic diseases. Consistent with its function relative to ghrelin, ghrelin O-acyltransferase can be found in all vertebrates, including mammals, birds, and fish species. The enzyme is primarily expressed in the stomach and the gastrointestinal system. Other sites where ghrelin O-acyltransferase can be found include tissue from the brain, the pancreas, the pituitary gland, and certain forms of cancer. Structure The structure of ghrelin o-acyltransferase has not been fully elucidated or tested experimentally. Using biochemical mapping tools, researchers showed that the ghrelin O-acyltransferase enzyme consists of eleven transmembrane helical domains and one reentrant loop. The C-terminus of ghrelin O-acyltransferase is located on the cytosolic side of the endoplasmic reticulum (ER) while the N-terminus resides in the lumen of the membrane. The topology models of ghrelin O-acyltransferase are similar to those of acetyl-coenzyme A acetyltransferase 1 and glycerol uptake protein 1. This is consistent with ghrelin O-acyltransferase being a member of the membrane bound O-acyl transferase family. Ghrelin O-acyltransferase contains conserved asparagine (Asn307) and histidine (His338) residues that are found across the membrane bound O-acyl transferase family. These amino acids are positioned on opposite side of the endoplasmic reticulum membrane. His338 resides in the lumen and is necessary for the observed catalytic activity of the enzyme. History The first reported discovery of ghrelin O-acyl transferase was in February 2008 by two separate research groups at Eli Lilly and the University of Texas at Austin (UT). The UT group identified orphan acyltransferase enzymes through the genome database and expressed both the enzymes in ghrelin in cells.[7] They found that membrane bound O-acyltransferase domain 4 specifically acylated ghrelin. The Eli Lilly team confirmed that enzyme is necessary to modify the ghrelin peptide by performing GOAT knock down experiments to prevent expression on the gene. Currently, the major pharmaceutical companies with patents related to ghrelin O-acyl