title: Biosynthesis of phosphoserine in the Methanococcales.
abstract: Methanococcus maripaludis and Methanocaldococcus jannaschii produce cysteine for protein synthesis using a tRNA-dependent pathway. These methanogens charge tRNA(Cys) with l-phosphoserine, which is also an intermediate in the predicted pathways for serine and cystathionine biosynthesis. To establish the mode of phosphoserine production in Methanococcales, cell extracts of M. maripaludis were shown to have phosphoglycerate dehydrogenase and phosphoserine aminotransferase activities. The heterologously expressed and purified phosphoglycerate dehydrogenase from M. maripaludis had enzymological properties similar to those of its bacterial homologs but was poorly inhibited by serine. While bacterial enzymes are inhibited by micromolar concentrations of serine bound to an allosteric site, the low sensitivity of the archaeal protein to serine is consistent with phosphoserine's position as a branch point in several pathways. A broad-specificity class V aspartate aminotransferase from M. jannaschii converted the phosphohydroxypyruvate product to phosphoserine. This enzyme catalyzed the transamination of aspartate, glutamate, phosphoserine, alanine, and cysteate. The M. maripaludis homolog complemented a serC mutation in the Escherichia coli phosphoserine aminotransferase. All methanogenic archaea apparently share this pathway, providing sufficient phosphoserine for the tRNA-dependent cysteine biosynthetic pathway.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Sunna
authors.initials: S
authors.lastname: Helgadóttir
authors.forename: Guillermina
authors.initials: G
authors.lastname: Rosas-Sandoval
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
authors.forename: David E
authors.initials: DE
authors.lastname: Graham
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D002846:Chromatography, Affinity; D003545:Cysteine / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D005816:Genetic Complementation Test; D017015:Methanococcales / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D050543:Phosphoglycerate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010768:Phosphoserine / Q000378:metabolism*; D010802:Phylogeny; D011773:Pyruvates / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D000637:Transaminases / Q000235:genetics / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D011773:Pyruvates; D010768:Phosphoserine; D001224:Aspartic Acid; C012488:phosphohydroxypyruvic acid; D012694:Serine; D050543:Phosphoglycerate Dehydrogenase; D000637:Transaminases; C022393:phosphoserine aminotransferase; D003545:Cysteine