title: Identification of the light-independent phosphoserine pathway as an additional source of serine in the cyanobacterium Synechocystis sp. PCC 6803.
abstract: L-serine is one of the proteinogenic amino acids and participates in several essential processes in all organisms. In plants, the light-dependent photorespiratory and the light-independent phosphoserine pathways contribute to serine biosynthesis. In cyanobacteria, the light-dependent photorespiratory pathway for serine synthesis is well characterized, but the phosphoserine pathway has not been identified. Here, we investigated three candidate genes for enzymes of the phosphoserine pathway in Synechocystis sp. PCC 6803. Only the gene for the D-3-phosphoglycerate dehydrogenase is correctly annotated in the genome database, whereas the 3-phosphoserine transaminase and 3-phosphoserine phosphatase (PSP) proteins are incorrectly annotated and were identified here. All enzymes were obtained as recombinant proteins and showed the activities necessary to catalyse the three-step phosphoserine pathway. The genes coding for the phosphoserine pathway were found in most cyanobacterial genomes listed in CyanoBase. The pathway seems to be essential for cyanobacteria, because it was impossible to mutate the gene coding for PSP in Synechocystis sp. PCC 6803 or in Synechococcus elongatus PCC 7942. A model approach indicates a 30-60% contribution of the phosphoserine pathway to the overall serine pool. Hence, this study verified that cyanobacteria, similar to plants, use the phosphoserine pathway in addition to photorespiration for serine biosynthesis.
authors.affiliation: Plant Biochemistry, Humboldt University Berlin, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Klemke
authors.affiliation: Plant Biochemistry, Humboldt University Berlin, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Baier
authors.affiliation: Institute of Theoretical Biology, Humboldt University Berlin, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Knoop
authors.affiliation: Department of Plant Physiology, University of Rostock, Germany.
authors.forename: Ramona
authors.initials: R
authors.lastname: Kern
authors.affiliation: Laboratory of Experimental Complex Systems, FFPW, University of South Bohemia, Czech Republic.
authors.forename: Jiri
authors.initials: J
authors.lastname: Jablonsky
authors.affiliation: Plant Biochemistry, Humboldt University Berlin, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Beyer
authors.affiliation: Plant Biochemistry, Humboldt University Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Volkmer
authors.affiliation: Institute of Theoretical Biology, Humboldt University Berlin, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Steuer
authors.affiliation: Plant Biochemistry, Humboldt University Berlin, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lockau
authors.affiliation: Department of Plant Physiology, University of Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Hagemann
mesh_terms: D000595:Amino Acid Sequence; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D008027:Light; D053858:Metabolic Networks and Pathways; D008969:Molecular Sequence Data; D050543:Phosphoglycerate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010768:Phosphoserine / Q000378:metabolism*; D016415:Sequence Alignment; D012694:Serine / Q000378:metabolism*; D013379:Substrate Specificity; D046939:Synechocystis / Q000502:physiology*
chemical_list: D010768:Phosphoserine; D012694:Serine; D050543:Phosphoglycerate Dehydrogenase