Lipid-binding START domain of mammalian STARDT14, -15, and related proteins
This subfamily includes the steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains of mammalian brown fat-inducible STARD14 (also known as Acyl-Coenzyme A Thioesterase 11 or ACOT11, BFIT, THEA, THEM1, KIAA0707, and MGC25974), STARD15/ACOT12 (also known as cytoplasmic acetyl-CoA hydrolase/CACH, THEAL, and MGC105114), and related domains. The START domain family belongs to the SRPBCC (START/RHO_alpha_C/PITP/Bet_v1/CoxG/CalC) domain superfamily of proteins that bind hydrophobic ligands. SRPBCC domains have a deep hydrophobic ligand-binding pocket. STARD14/ACOT11 and STARD15/ACOT12 are type II acetyl-CoA thioesterases; they catalyze the hydrolysis of acyl-CoAs to free fatty acid and CoASH. Human STARD14 displays acetyl-CoA thioesterase activity towards medium(C12)- and long(C16)-chain fatty acyl-CoA substrates. Rat CACH hydrolyzes acetyl-CoA to acetate and CoA. In addition to having a START domain, STARD14 and STARD15 each have two tandem copies of the hotdog domain. There are two splice variants of human STARD14, named BFIT1 and BFIT2, which differ in their C-termini. Human BFIT2 is equivalent to mouse mBFIT/Acot11, whose transcription is increased two fold in obesity-resistant mice compared with obesity-prone mice. Human STARD15 may have roles in cholesterol metabolism and in beta-oxidation.