title: Crystallization and preliminary crystallographic characterization of glutamine synthetase from Medicago truncatula.
abstract: The condensation of ammonium and glutamate into glutamine catalyzed by glutamine synthetase (GS) is a fundamental step in nitrogen metabolism in all kingdoms of life. In plants, this is preceded by the reduction of inorganic nitrogen to an ammonium ion and therefore effectively articulates nitrogen fixation and metabolism. Although the three-dimensional structure of the dodecameric bacterial GS was determined quite some time ago, the quaternary architecture of the plant enzyme has long been assumed to be octameric, mostly on the basis of low-resolution electron-microscopy studies. Recently, the crystallographic structure of a monocotyledonous plant GS was reported that revealed a homodecameric organization. In order to unambiguously establish the quaternary architecture of GS from dicotyledonous plants, GS1a from the model legume Medicago truncatula was overexpressed, purified and crystallized. The collection of synchrotron diffraction data to 2.35 A resolution allowed the determination of the three-dimensional structure of this enzyme by molecular replacement.
authors.affiliation: IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal.
authors.forename: Ana Rita
authors.initials: AR
authors.lastname: Seabra
authors.forename: Helena
authors.initials: H
authors.lastname: Carvalho
authors.forename: Pedro José Barbosa
authors.initials: PJ
authors.lastname: Pereira
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D018360:Crystallography, X-Ray; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry* / Q000235:genetics; D046913:Medicago truncatula / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D011993:Recombinant Fusion Proteins; D005974:Glutamate-Ammonia Ligase