title: Crystal structure of threonine synthase from Arabidopsis thaliana.
abstract: Threonine synthase (TS) is a PLP-dependent enzyme that catalyzes the last reaction in the synthesis of threonine from aspartate. In plants, the methionine pathway shares the same substrate, O-phospho-L-homoserine (OPH), and TS is activated by S-adenosyl-methionine (SAM), a downstream product of methionine synthesis. This positive allosteric effect triggered by the product of another pathway is specific to plants. The crystal structure of Arabidopsis thaliana apo threonine synthase was solved at 2.25 A resolution from triclinic crystals using MAD data from the selenomethionated protein. The structure reveals a four-domain dimer with a two-stranded beta-sheet arm protruding from one monomer onto the other. This domain swap could form a lever through which the allosteric effect is transmitted. The N-terminal domain (domain 1) has a unique fold and is partially disordered, whereas the structural core (domains 2 and 3) shares the functional domain of PLP enzymes of the same family. It also has similarities with SAM-dependent methyltransferases. Structure comparisons allowed us to propose potential sites for pyridoxal-phosphate and SAM binding on TS; they are close to regions that are disordered in the absence of these molecules.
authors.affiliation: Institut de Biologie Structurale Jean-Pierre Ebel, Unité Mixte de Recherche 5075 Centre National de la Recherche Scientifique-Centre d'Etudes Nucléaires-Université Joseph Fourier, F-38027 Grenoble, France.
authors.forename: K
authors.initials: K
authors.lastname: Thomazeau
authors.forename: G
authors.initials: G
authors.lastname: Curien
authors.forename: R
authors.initials: R
authors.lastname: Dumas
authors.forename: V
authors.initials: V
authors.lastname: Biou
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology; D001665:Binding Sites; D019757:Carbon-Oxygen Lyases / Q000737:chemistry* / Q000378:metabolism*; D017124:Conserved Sequence; D003461:Crystallography; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011732:Pyridoxal Phosphate / Q000737:chemistry* / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D011732:Pyridoxal Phosphate; D012436:S-Adenosylmethionine; D019757:Carbon-Oxygen Lyases; C023160:threonine synthase