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Catalytic Trimer (catalytic + trimer)
Selected AbstractsRefined structure of Pyrococcus furiosus ornithine carbamoyltransferase at 1.87,AACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2003Jan Massant Using synchrotron radiation, X-ray data have been collected from Pyrococcus furiosus ornithine carbamoyltransferase (Pfu OTCase) to a maximal resolution of 1.87,Å, allowing the refinement of a previous structure at 2.7,Å [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,, interactions. [source] Crystallization and structure determination of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2000Jacqueline Vitali Aspartate transcarbamoylase (ATCase) catalyzes the first step in the pyrimidine biosynthetic pathway, the reaction between carbamoyl phosphate and l -aspartate to form N -carbamoyl- l -aspartate and phosphate. The structural analysis of the ATCase catalytic trimer from Methanococcus jannaschii, a unicellular thermophilic archaeabacterium, has been undertaken in order to gain insight into the structural features that are responsible for the thermostability of the enzyme. As a first step, the catalytic trimer was crystallized in space group R32, with unit-cell parameters a = b = 265.3, c = 195.5,Å and two trimers in the asymmetric unit. Its structure was determined using molecular replacement and Patterson methods. In general, structures containing multiple copies of molecules in the asymmetric unit are difficult to determine. In this case, the two trimers in the asymmetric unit are parallel to each other and use of the Patterson function greatly simplified the structure solution. [source] Structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal formACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2008Jacqueline Vitali Crystals of the catalytic subunit of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form contain four crystallographically independent trimers which associate in pairs to form stable staggered complexes that are similar to each other and to a previously determined monoclinic C2 form. Each subunit has a sulfate in the central channel. The catalytic subunits in these complexes show flexibility, with the elbow angles of the monomers differing by up to 7.4° between crystal forms. Moreover, there is also flexibility in the relative orientation of the trimers around their threefold axis in the complexes, with a difference of 4° between crystal forms. [source] Probing the role of oligomerization in the high thermal stability of Pyrococcus furiosus ornithine carbamoyltransferase by site-specific mutantsFEBS JOURNAL, Issue 14 2001Bernard Clantin The Pyrococcus furiosus ornithine carbamoyltransferase (OTCase) is extremely heat stable and maintains 50% of its catalytic activity after 60 min at 100 °C. The enzyme has an unusual quaternary structure when compared to anabolic OTCases from mesophilic organisms. It is built up of four trimers arranged in a tetrahedral manner, while other anabolic enzymes are single trimers. Residues Trp21, Glu25, Met29 and Trp33 are located in the main interfaces that occur between the catalytic trimers within the dodecamer. They participate in either hydrophobic clusters or ionic interactions. In order to elucidate the role played by the oligomerization in the enzyme stability at very high temperatures, we performed mutagenesis studies of these residues. All the variants show similar catalytic activities and kinetic properties when compared to the wild-type enzyme, allowing the interpretation of the mutations solely on heat stability and quaternary structure. The W21A variant has only a slight decrease in its stability, and is a dodecamer. The variants E25Q, M29A, W33A, W21A/W33A and E25Q/W33A show that altering more drastically the interfaces results in a proportional decrease in heat stability, correlated with a gradual dissociation of dodecamers into trimers. Finally, the E25Q/M29A/W33A variant shows a very large decrease in heat stability and is a trimer. These results suggest that extreme thermal stabilization of this OTCase is achieved in part through oligomerization. [source] Refined structure of Pyrococcus furiosus ornithine carbamoyltransferase at 1.87,AACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2003Jan Massant Using synchrotron radiation, X-ray data have been collected from Pyrococcus furiosus ornithine carbamoyltransferase (Pfu OTCase) to a maximal resolution of 1.87,Å, allowing the refinement of a previous structure at 2.7,Å [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,, interactions. [source] | ||||||||||