Refined structure of Pyrococcus furiosus ornithine carbamoyltransferase at 1.87 A.
Using synchrotron radiation, X-ray data have been collected from Pyrococcus furiosus ornithine carbamoyltransferase (Pfu OTCase) to a maximal resolution of 1.87 A, allowing the refinement of a previous structure at 2.7 A [Villeret et al. (1998), Proc. Natl Acad. Sci. USA, 95, 2801-2806]. Thanks to the high resolution of this refined structure, two sulfate ions and 191 water molecules could be localized directly from the electron-density maps. The identification of these molecules allowed a more rigorous description of the active site and the identification of residues involved in binding carbamoyl phosphate. The improved quality of the model resulted in a better definition of several loops and the various interfaces. The dodecameric protein is composed of four catalytic trimers disposed in a tetrahedral manner. The extreme thermal stability of Pfu OTCase is mainly the result of the strengthening of the intersubunit interactions in a trimer and oligomerization of the trimers into a dodecamer. Interfaces between monomers in a catalytic trimer are characterized by an increase in ion-pair networks compared with mesophilic OTCases. However, the interfaces between catalytic trimers in the dodecameric oligomer are mainly hydrophobic and also involve aromatic-aromatic and cation-pi interactions.
Massant
Jan
J
Department of Microbiology, Vrije Universiteit Brussel, B-1070 Brussels, Belgium. jan.massant@vub.ac.be
Wouters
Johan
J
Glansdorff
Nicolas
N
D000596:Amino Acids / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D009954:Ornithine Carbamoyltransferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D020027:Pyrococcus furiosus / Q000201:enzymology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D012997:Solvents / Q000737:chemistry; D055672:Static Electricity; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D017356:Synchrotrons
D000596:Amino Acids; D011994:Recombinant Proteins; D012997:Solvents; D013431:Sulfates; D009954:Ornithine Carbamoyltransferase