title: Glycerate kinase of the hyperthermophilic archaeon Thermoproteus tenax: new insights into the phylogenetic distribution and physiological role of members of the three different glycerate kinase classes.
abstract: BACKGROUND
  The presence of the branched Entner-Doudoroff (ED) pathway in two hyperthermophilic Crenarchaea, the anaerobe Thermoproteus tenax and the aerobe Sulfolobus solfataricus, was suggested. However, so far no enzymatic information of the non-phosphorylative ED branch and especially its key enzyme - glycerate kinase - was available. In the T. tenax genome, a gene homolog with similarity to putative hydroxypyruvate reductase/glycerate dehydrogenase and glycerate kinase was identified.
  
  
  RESULTS
  The encoding gene was expressed in E. coli in a recombinant form, the gene product purified and the glycerate kinase activity was confirmed by enzymatic studies. The enzyme was active as a monomer and catalyzed the ATP-dependent phosphorylation of D-glycerate forming exclusively 2-phosphoglycerate. The enzyme was specific for glycerate and highest activity was observed with ATP as phosphoryl donor and Mg2+ as divalent cation. ATP could be partially replaced by GTP, CTP, TTP and UTP. The enzyme showed high affinity for D-glycerate (Km 0.02 +/- 0.01 mM, Vmax of 5.05 +/- 0.52 U/mg protein) as well as ATP (Km of 0.03 +/- 0.01 mM, Vmax of 4.41 +/- 0.04 U/mg protein), although at higher glycerate concentrations, substrate inhibition was observed. Furthermore, the enzyme was inhibited by its product ADP via competitive inhibition. Data bank searches revealed that archaeal glycerate kinases are members of the MOFRL (multi-organism fragment with rich leucine) family, and homologs are found in all three domains of life.
  
  
  CONCLUSIONS
  A re-evaluation of available genome sequence information as well as biochemical and phylogenetic studies revealed the presence of the branched ED pathway as common route for sugar degradation in Archaea that utilize the ED pathway. Detailed analyses including phylogenetic studies demonstrate the presence of three distinct glycerate kinase classes in extant organisms that share no common origin. The affiliation of characterized glycerate kinases with the different enzyme classes as well as their physiological/cellular function reveals no association with particular pathways but a separate phylogenetic distribution. This work highlights the diversity and complexity of the central carbohydrate metabolism. The data also support a key function of the conversion of glycerate to 2- or 3-phosphoglycerate via glycerate kinase in funneling various substrates into the common EMP pathway for catabolic and anabolic purposes.
authors.affiliation: Department of Biology and Geography, Institute of Biology, Microbiology I, Universität Duisburg-Essen, Universitätsstr, 5, 45117 Essen, Germany. daniel.kehrer@stud.uni-due.de
authors.forename: Daniel
authors.initials: D
authors.lastname: Kehrer
authors.forename: Hatim
authors.initials: H
authors.lastname: Ahmed
authors.forename: Henner
authors.initials: H
authors.lastname: Brinkmann
authors.forename: Bettina
authors.initials: B
authors.lastname: Siebers
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D002384:Catalysis; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000145:classification / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D041542:Thermoproteus / Q000201:enzymology*
chemical_list: D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020670:glycerate kinase