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|2ib7, resolution 2.05Å ()|
|Gene:||ACAT1 (Homo sapiens)|
|Related:||2ib8, 2ib9, 2ibu, 2ibw, 2iby|
Crystallographic and kinetic studies of human mitochondrial acetoacetyl-CoA thiolase (T2): the importance of potassium and chloride for its structure and function
Thiolases are CoA-dependent enzymes which catalyze the formation of a carbon-carbon bond in a Claisen condensation step and its reverse reaction via a thiolytic degradation mechanism. Mitochondrial acetoacetyl-coenzyme A (CoA) thiolase (T2) is important in the pathways for the synthesis and degradation of ketone bodies as well as for the degradation of 2-methylacetoacetyl-CoA. Human T2 deficiency has been identified in more than 60 patients. A unique property of T2 is its activation by potassium ions. High-resolution human T2 crystal structures are reported for the apo form and the CoA complex, with and without a bound potassium ion. The potassium ion is bound near the CoA binding site and the catalytic site. Binding of the potassium ion at this low-affinity binding site causes the rigidification of a CoA binding loop and an active site loop. Unexpectedly, a high-affinity binding site for a chloride ion has also been identified. The chloride ion is copurified, and its binding site is at the dimer interface, near two catalytic loops. A unique property of T2 is its ability to use 2-methyl-branched acetoacetyl-CoA as a substrate, whereas the other structurally characterized thiolases cannot utilize the 2-methylated compounds. The kinetic measurements show that T2 can degrade acetoacetyl-CoA and 2-methylacetoacetyl-CoA with similar catalytic efficiencies. For both substrates, the turnover numbers increase approximately 3-fold when the potassium ion concentration is increased from 0 to 40 mM KCl. The structural analysis of the active site of T2 indicates that the Phe325-Pro326 dipeptide near the catalytic cavity is responsible for the exclusive 2-methyl-branched substrate specificity.
Crystallographic and kinetic studies of human mitochondrial acetoacetyl-CoA thiolase: the importance of potassium and chloride ions for its structure and function., Haapalainen AM, Merilainen G, Pirila PL, Kondo N, Fukao T, Wierenga RK, Biochemistry. 2007 Apr 10;46(14):4305-21. Epub 2007 Mar 20. PMID:17371050
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
[THIL_HUMAN] Defects in ACAT1 are a cause of 3-ketothiolase deficiency (3KTD) [MIM:203750]; also known as alpha-methylacetoaceticaciduria. 3KTD is an inborn error of isoleucine catabolism characterized by intermittent ketoacidotic attacks associated with unconsciousness. Some patients die during an attack or are mentally retarded. Urinary excretion of 2-methyl-3-hydroxybutyric acid, 2-methylacetoacetic acid, triglylglycine, butanone is increased. It seems likely that the severity of this disease correlates better with the environmental or acquired factors than with the ACAT1 genotype.
[THIL_HUMAN] Plays a major role in ketone body metabolism.
About this Structure
- Haapalainen AM, Merilainen G, Pirila PL, Kondo N, Fukao T, Wierenga RK. Crystallographic and kinetic studies of human mitochondrial acetoacetyl-CoA thiolase: the importance of potassium and chloride ions for its structure and function. Biochemistry. 2007 Apr 10;46(14):4305-21. Epub 2007 Mar 20. PMID:17371050 doi:10.1021/bi6026192
- ↑ Fukao T, Yamaguchi S, Orii T, Schutgens RB, Osumi T, Hashimoto T. Identification of three mutant alleles of the gene for mitochondrial acetoacetyl-coenzyme A thiolase. A complete analysis of two generations of a family with 3-ketothiolase deficiency. J Clin Invest. 1992 Feb;89(2):474-9. PMID:1346617 doi:http://dx.doi.org/10.1172/JCI115608
- ↑ Fukao T, Yamaguchi S, Tomatsu S, Orii T, Frauendienst-Egger G, Schrod L, Osumi T, Hashimoto T. Evidence for a structural mutation (347Ala to Thr) in a German family with 3-ketothiolase deficiency. Biochem Biophys Res Commun. 1991 Aug 30;179(1):124-9. PMID:1715688
- ↑ Wakazono A, Fukao T, Yamaguchi S, Hori T, Orii T, Lambert M, Mitchell GA, Lee GW, Hashimoto T. Molecular, biochemical, and clinical characterization of mitochondrial acetoacetyl-coenzyme A thiolase deficiency in two further patients. Hum Mutat. 1995;5(1):34-42. PMID:7728148 doi:http://dx.doi.org/10.1002/humu.1380050105
- ↑ Fukao T, Nakamura H, Song XQ, Nakamura K, Orii KE, Kohno Y, Kano M, Yamaguchi S, Hashimoto T, Orii T, Kondo N. Characterization of N93S, I312T, and A333P missense mutations in two Japanese families with mitochondrial acetoacetyl-CoA thiolase deficiency. Hum Mutat. 1998;12(4):245-54. PMID:9744475 doi:<245::AID-HUMU5>3.0.CO;2-E 10.1002/(SICI)1098-1004(1998)12:4<245::AID-HUMU5>3.0.CO;2-E