title: A specialized aspartokinase enhances the biosynthesis of the osmoprotectants ectoine and hydroxyectoine in Pseudomonas stutzeri A1501.
abstract: The compatible solutes ectoine and hydroxyectoine are widely produced by bacteria as protectants against osmotic and temperature stress. l-Aspartate-beta-semialdehyde is used as the precursor molecule for ectoine/hydroxyectoine biosynthesis that is catalyzed by the EctABCD enzymes. l-Aspartate-beta-semialdehyde is a central intermediate in different biosynthetic pathways and is produced from l-aspartate by aspartokinase (Ask) and aspartate-semialdehyde-dehydrogenase (Asd). Ask activity is typically stringently regulated by allosteric control to avoid gratuitous synthesis of aspartylphosphate. Many organisms have evolved multiple forms of aspartokinase, and feedback regulation of these specialized Ask enzymes is often adapted to the cognate biochemical pathways. The ectoine/hydroxyectoine biosynthetic genes (ectABCD) are followed in a considerable number of microorganisms by an askgene (ask_ect), suggesting that Ask_Ect is a specialized enzyme for this osmoadaptive biosynthetic pathway. However, none of these Ask_Ect enzymes have been functionally characterized. Pseudomonas stutzeri A1501 synthesizes both ectoine and hydroxyectoine in response to increased salinity, and it possesses two Ask enzymes: Ask_Lys and Ask_Ect. We purified both Ask enzymes and found significant differences with regard to their allosteric control: Ask_LysC was inhibited by threonine and in a concerted fashion by threonine and lysine, whereas Ask_Ect showed inhibition only by threonine. The ectABCD_askgenes from P. stutzeri A1501 were cloned and functionally expressed in Escherichia coli, and this led to osmostress protection. An E. colistrain carrying the plasmid-based ectABCD_askgene cluster produced significantly more ectoine/hydroxyectoine than a strain expressing the ectABCDgene cluster alone. This finding suggests a specialized role for Ask_Ect in ectoine/hydroxyectoine biosynthesis.
authors: Philipps-University Marburg, Department of Biology, Laboratory for Microbiology, Karl-von-Frisch Str. 8, D-35032 Marburg, Germany.
authors: Nadine
authors: N
authors: Stöveken
authors: Marco
authors: M
authors: Pittelkow
authors: Tatjana
authors: T
authors: Sinner
authors: Roy A
authors: RA
authors: Jensen
authors: Johann
authors: J
authors: Heider
authors: Erhard
authors: E
authors: Bremer
mesh_terms: D000599:Amino Acids, Diamino / Q000096:biosynthesis*; D001222:Aspartate Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001223:Aspartate-Semialdehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D008239:Lysine / Q000378:metabolism; D005810:Multigene Family; D010957:Plasmids; D044223:Pseudomonas stutzeri / Q000201:enzymology / Q000235:genetics*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013312:Stress, Physiological; D013912:Threonine / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D000599:Amino Acids, Diamino; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011994:Recombinant Proteins; C121557:hydroxyectoine; D013912:Threonine; D001224:Aspartic Acid; C006644:aspartic semialdehyde; C045628:ectoine; D001223:Aspartate-Semialdehyde Dehydrogenase; C116188:lysC aspartokinase; D001222:Aspartate Kinase; D008239:Lysine