title: The crystal structure of murine CMP-5-N-acetylneuraminic acid synthetase.
abstract: Sialic acids are activated by CMP-5-N-acetylneuraminic acid synthetase prior to their transfer onto oligo- or polysaccharides. Here, we present the crystal structure of the N-terminal catalytically active domain of the murine 5-N-acetylneuraminic acid synthetase in complex with the reaction product. In contrast to the previously solved structure of 5-N-acetylneuraminic acid synthetase from Neisseria meningitidis and the related CMP-KDO-synthetase of Escherichia coli, the murine enzyme is a tetramer, which was observed with the active sites closed. In this conformation a loop is shifted by 6A towards the active site and thus an essential arginine residue can participate in catalysis. Furthermore, a network of intermolecular salt-bridges and hydrogen bonds in the dimer as well as hydrophobic interfaces between two dimers indicate a cooperative behaviour of the enzyme. In addition, a complex regulation of the enzyme activity is proposed that includes phosphorylation and dephosphorylation.
authors.affiliation: Max-Planck-Institut für Biochemie, Abteilung für Strukturforschung, Am Klopferspitz 18a, 82152, Martinsried, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Krapp
authors.forename: Anja K
authors.initials: AK
authors.lastname: Münster-Kühnel
authors.forename: Jens T
authors.initials: JT
authors.lastname: Kaiser
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Joe
authors.initials: J
authors.lastname: Tiralongo
authors.forename: Rita
authors.initials: R
authors.lastname: Gerardy-Schahn
authors.forename: Uwe
authors.initials: U
authors.lastname: Jacob
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D000216:N-Acylneuraminate Cytidylyltransferase / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D000216:N-Acylneuraminate Cytidylyltransferase