title: Molecular cloning of a novel glucuronokinase/putative pyrophosphorylase from zebrafish acting in an UDP-glucuronic acid salvage pathway.
abstract: In animals, the main precursor for glycosaminoglycan and furthermore proteoglycan biosynthesis, like hyaluronic acid, is UDP-glucuronic acid, which is synthesized via the nucleotide sugar oxidation pathway. Mutations in this pathway cause severe developmental defects (deficiency in the initiation of heart valve formation). In plants, UDP-glucuronic acid is synthesized via two independent pathways. Beside the nucleotide sugar oxidation pathway, a second minor route to UDP-glucuronic acid exist termed the myo-inositol oxygenation pathway. Within this myo-inositol is ring cleaved into glucuronic acid, which is subsequently converted to UDP-glucuronic acid by glucuronokinase and UDP-sugar pyrophosphorylase. Here we report on a similar, but bifunctional enzyme from zebrafish (Danio rerio) which has glucuronokinase/putative pyrophosphorylase activity. The enzyme can convert glucuronic acid into UDP-glucuronic acid, required for completion of the alternative pathway to UDP-glucuronic acid via myo-inositol and thus establishes a so far unknown second route to UDP-glucuronic acid in animals. Glucuronokinase from zebrafish is a member of the GHMP-kinase superfamily having unique substrate specificity for glucuronic acid with a Km of 31 ± 8 µM and accepting ATP as the only phosphate donor (Km: 59 ± 9 µM). UDP-glucuronic acid pyrophosphorylase from zebrafish has homology to bacterial nucleotidyltransferases and requires UTP as nucleosid diphosphate donor. Genes for bifunctional glucuronokinase and putative UDP-glucuronic acid pyrophosphorylase are conserved among some groups of lower animals, including fishes, frogs, tunicates, and polychaeta, but are absent from mammals. The existence of a second pathway for UDP-glucuronic acid biosynthesis in zebrafish likely explains some previous contradictory finding in jekyll/ugdh zebrafish developmental mutants, which showed residual glycosaminoglycans and proteoglycans in knockout mutants of UDP-glucose dehydrogenase.
authors.affiliation: Department of Cell Biology, Division Plant Physiology, University of Salzburg, Salzburg, Austria.
authors.forename: Roman
authors.initials: R
authors.lastname: Gangl
authors.affiliation: Department of Cell Biology, Division Plant Physiology, University of Salzburg, Salzburg, Austria ; Department of Molecular Biology, Division of Chemistry and Bioanalytics, University of Salzburg, Salzburg, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Behmüller
authors.affiliation: Department of Cell Biology, Division Plant Physiology, University of Salzburg, Salzburg, Austria.
authors.forename: Raimund
authors.initials: R
authors.lastname: Tenhaken
mesh_terms: D000818:Animals; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D014533:Uridine Diphosphate Glucose Dehydrogenase / Q000378:metabolism; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000378:metabolism*
chemical_list: D029961:Zebrafish Proteins; D014535:Uridine Diphosphate Glucuronic Acid; D014533:Uridine Diphosphate Glucose Dehydrogenase; D017853:Phosphotransferases (Alcohol Group Acceptor); C020591:glucuronokinase