Acyl-CoA-binding protein, ACBP <p>Acyl-CoA-binding protein (ACBP) is a small (10 Kd) protein that binds medium- and long-chain acyl-CoA esters with very high affinity and may function as an intracellular carrier of acyl-CoA esters [<cite idref="PUB00004768"/>]. ACBP is also known as diazepam binding inhibitor (DBI) or endozepine (EP) because of its ability to displace diazepam from the benzodiazepine (BZD) recognition site located on the GABA type A receptor. It is therefore possible that this protein also acts as a neuropeptide to modulate the action of the GABA receptor [<cite idref="PUB00003552"/>].</p><p>ACBP is a highly conserved protein of about 90 residues that is found in all four eukaryotic kingdoms, Animalia, Plantae, Fungi and Protista, and in some eubacterial species [<cite idref="PUB00035335"/>].</p><p>Although ACBP occurs as a completely independent protein, intact ACB domains have been identified in a number of large, multifunctional proteins in a variety of eukaryotic species. These include large membrane-associated proteins with N-terminal ACB domains, multifunctional enzymes with both ACB and peroxisomal enoyl-CoA Delta(3), Delta(2)-enoyl-CoA isomerase domains, and proteins with both an ACB domain and ankyrin repeats (<db_xref db="INTERPRO" dbkey="IPR002110"/>) [<cite idref="PUB00035335"/>].</p><p>The ACB domain consists of four alpha-helices arranged in a bowl shape with ahighly exposed acyl-CoA-binding site. The ligand is boundthrough specific interactions with residues on the protein, most notablyseveral conserved positive charges that interact with the phosphate group onthe adenosine-3'phosphate moiety, and the acyl chain is sandwiched between thehydrophobic surfaces of CoA and the protein [<cite idref="PUB00021736"/>].</p><p>Other proteins containing an ACB domain include:<ul><li> Endozepine-like peptide (ELP) (gene DBIL5) from mouse [<cite idref="PUB00003711"/>]. ELP is a testis-specific ACBP homologue that may be involved in the energy metabolism of the mature sperm.</li><li>MA-DBI, a transmembrane protein of unknown function which has been found in mammals. MA-DBI contains a N-terminal ACB domain.</li><li>DRS-1 [<cite idref="PUB00000679"/>], a human protein of unknown function that contains a N-terminal ACB domain and a C-terminal enoyl-CoA isomerase/hydratase domain.</li></ul></p>