1WL5: Human Cytosolic Acetoacetyl-Coa Thiolase

Citation:
Abstract
Thiolases belong to a superfamily of condensing enzymes that includes also beta-ketoacyl acyl carrier protein synthases (KAS enzymes), involved in fatty acid synthesis. Here, we describe the high resolution structure of human cytosolic acetoacetyl-CoA thiolase (CT), both unliganded (at 2.3 angstroms resolution) and in complex with CoA (at 1.6 angstroms resolution). CT catalyses the condensation of two molecules of acetyl-CoA to acetoacetyl-CoA, which is the first reaction of the metabolic pathway leading to the synthesis of cholesterol. CT is a homotetramer of exact 222 symmetry. There is an excess of positively charged residues at the interdimer surface leading towards the CoA-binding pocket, possibly important for the efficient capture of substrates. The geometry of the catalytic site, including the three catalytic residues Cys92, His 353, Cys383, and the two oxyanion holes, is highly conserved between the human and bacterial Zoogloea ramigera thiolase. In human CT, the first oxyanion hole is formed by Wat38 (stabilised by Asn321) and NE2(His353), and the second by N(Cys92) and N(Gly385). The active site of this superfamily is constructed on top of four active site loops, near Cys92, Asn321, His353, and Cys383, respectively. These loops were used for the superpositioning of CT on the bacterial thiolase and on the Escherichia coli KAS I. This comparison indicates that the two thiolase oxyanion holes also exist in KAS I at topologically equivalent positions. Interestingly, the hydrogen bonding interactions at the first oxyanion hole are different in thiolase and KAS I. In KAS I, the hydrogen bonding partners are two histidine NE2 atoms, instead of a water and a NE2 side-chain atom in thiolase. The second oxyanion hole is in both structures shaped by corresponding main chain peptide NH-groups. The possible importance of bound water molecules at the catalytic site of thiolase for the reaction mechanism is discussed.
PDB ID: 1WL5Download
MMDB ID: 31913
PDB Deposition Date: 2004/6/20
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 2.26  Å
Source Organism:
Similar Structures:
Biological Unit for 1WL5: tetrameric; determined by author and by software (PISA,PQS)
Molecular Components in 1WL5
Label Count Molecule
Proteins (4 molecules)
4
Acetyl-coenzyme a Acetyltransferase 2(Gene symbol: ACAT2)
Molecule annotation
Chemicals (20 molecules)
1
12
2
8
* Click molecule labels to explore molecular sequence information.

Citing MMDB
.