title: Thioesterase superfamily member 2 (Them2)/acyl-CoA thioesterase 13 (Acot13): a homotetrameric hotdog fold thioesterase with selectivity for long-chain fatty acyl-CoAs.
abstract: Them2 (thioesterase superfamily member 2) is a 140-amino-acid protein of unknown biological function that comprises a single hotdog fold thioesterase domain. On the basis of its putative association with mitochondria, accentuated expression in oxidative tissues and interaction with StarD2 (also known as phosphatidylcholine-transfer protein, PC-TP), a regulator of fatty acid metabolism, we explored whether Them2 functions as a physiologically relevant fatty acyl-CoA thioesterase. In solution, Them2 formed a stable homotetramer, which denatured in a single transition at 59.3 degrees C. Them2 exhibited thioesterase activity for medium- and long-chain acyl-CoAs, with Km values that decreased exponentially as a function of increasing acyl chain length. Steady-state kinetic parameters for Them2 were characteristic of long-chain mammalian acyl-CoA thioesterases, with minimal values of Km and maximal values of kcat/Km observed for myristoyl-CoA and palmitoyl-CoA. For these acyl-CoAs, substrate inhibition was observed when concentrations approached their critical micellar concentrations. The acyl-CoA thioesterase activity of Them2 was optimized at physiological temperature, ionic strength and pH. For both myristoyl-CoA and palmitoyl-CoA, the addition of StarD2 increased the kcat of Them2. Enzymatic activity was decreased by the addition of phosphatidic acid/phosphatidylcholine small unilamellar vesicles. Them2 expression, which was most pronounced in mouse heart, was associated with mitochondria and was induced by activation of PPARalpha (peroxisome-proliferator-activated receptor alpha). We conclude that, under biological conditions, Them2 probably functions as a homotetrameric long-chain acyl-CoA thioesterase. Accordingly, Them2 has been designated as the 13th member of the mammalian acyl-CoA thioesterase family, Acot13.
authors.affiliation: Department of Medicine, Division of Gastroenterology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Wei
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Kang
authors.forename: David E
authors.initials: DE
authors.lastname: Cohen
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D050356:Lipid Metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009994:Osmolar Concentration; D017510:Protein Folding; D013379:Substrate Specificity; D013696:Temperature; D013869:Thiolester Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; C040349:S-tetradecanoyl-coenzyme A; C514740:ACOT13 protein, human; C544602:Acot13 protein, mouse; D013869:Thiolester Hydrolases