PDBsum entry 2ib9

Transferase

PDB id: 2ib9

Contents

Protein chains

391 a.a. *

Ligands

MES ×4

GOL ×5

Metals

_CL ×4

__K ×4

Waters ×938

* Residue conservation analysis

PDB id:

2ib9

Name:

Transferase

Title:

Crystallographic and kinetic studies of human mitochondrial acetoacetyl-coa thiolase (t2): the importance of potassium and chloride for its structure and function

Structure:

Acetyl-coa acetyltransferase. Chain: a, b, c, d. Synonym: acetoacetyl-coa thiolase, t2. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Tissue: liver. Gene: acat1. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

2.05Å R-factor: 0.158 R-free: 0.199

Authors:

A.M.Haapalainen,R.K.Wierenga

Key ref:

A.M.Haapalainen et al. (2007). Crystallographic and kinetic studies of human mitochondrial acetoacetyl-CoA thiolase: the importance of potassium and chloride ions for its structure and function. Biochemistry, 46, 4305-4321. PubMed id: 17371050

Date:

11-Sep-06 Release date: 03-Apr-07

Protein chains

P24752  (THIL_HUMAN) -  Acetyl-CoA acetyltransferase, mitochondrial from Homo sapiens

Seq: 427 a.a.

Struc: 391 a.a.

Enzyme reactions

• Enzyme class: E.C.2.3.1.9 - acetyl-CoA C-acetyltransferase.
• Pathway: Mevalonate Biosynthesis
• Reaction: 2 acetyl-CoA = acetoacetyl-CoA + CoA

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

Biochemistry 46:4305-4321 (2007)

PubMed id: 17371050

Crystallographic and kinetic studies of human mitochondrial acetoacetyl-CoA thiolase: the importance of potassium and chloride ions for its structure and function.

A.M.Haapalainen, G.Meriläinen, P.L.Pirilä, N.Kondo, T.Fukao, R.K.Wierenga.

ABSTRACT

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.