Journal
BIOCHEMICAL JOURNAL
Volume 421, Issue -, Pages 311-322Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20090039
Keywords
fatty acid; fatty acyl-CoA; homotetramer; hotdog fold thioesterase; phospholipid; StarD2
Categories
Funding
- National Institutes of Health [DK-56626, DK-48873]
- American Heart Association
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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 K-m values that decreased exponentially its 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 K-m and maximal values of k(cat)/K-m 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 k(cat) 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 PPAR alpha (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, Acot 13.
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