1FB5: Low Resolution Structure Of Ovine Ornithine Transcarbmoylase In The Unliganded State

Citation:
Abstract
Ornithine transcarbamoylase from ovine liver has been purified to homogeneity. Like all anabolic OTCs, the ovine enzyme is a trimer, constituted by identical subunits of 34 kDa. Sequence analysis of the 54 N-terminal residues of ovine OTC shows a high degree of homology with the human enzyme. The optimum pH and the Michaelis constants for the catalytic reaction were determined. The ovine enzyme is the most thermostable one among mammals OTCs, its critical temperature being 6 degrees C higher than those measured for the other enzymes. The enzyme has been crystallised and the structure determined at 3.5 A resolution. Crystals belong to the cubic P4(3)32 space group, with a = b = c = 184.7 A and a solvent content of about 80%. There is no evidence of any ligand in the active site cavity, indicating that the crystals contain an unliganded or T state of the enzyme. The unliganded OTCase enzyme adopts a trimeric structure which, in the crystal, presents a three-fold axis coincident with the crystallographic one. The conformation of each monomer in the trimer is quite similar to that of the liganded human protein, with the exception of a few loops, directly interacting with the substrate(s), which are able to induce a rearrangement of the quaternary organisation of the trimer, that accounts for the cooperative behaviour of the enzyme following the binding of the substrates.
PDB ID: 1FB5Download
MMDB ID: 23974
PDB Deposition Date: 2000/7/14
Updated in MMDB: 2003/11
Experimental Method:
x-ray diffraction
Resolution: 3.5  Å
Source Organism:
Similar Structures:
Biological Unit for 1FB5: trimeric; determined by author and by software (PISA,PQS)
Molecular Components in 1FB5
Label Count Molecule
Proteins (3 molecules)
3
Ornithine Transcarbamoylase(Gene symbol: OTC)
Molecule annotation
Chemicals (3 molecules)
1
3
* Click molecule labels to explore molecular sequence information.

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