title: Revealing the functions of the transketolase enzyme isoforms in Rhodopseudomonas palustris using a systems biology approach.
abstract: BACKGROUND
  Rhodopseudomonas palustris (R. palustris) is a purple non-sulfur anoxygenic phototrophic bacterium that belongs to the class of proteobacteria. It is capable of absorbing atmospheric carbon dioxide and converting it to biomass via the process of photosynthesis and the Calvin-Benson-Bassham (CBB) cycle. Transketolase is a key enzyme involved in the CBB cycle. Here, we reveal the functions of transketolase isoforms I and II in R. palustris using a systems biology approach.
  
  
  RESULTS
  By measuring growth ability, we found that transketolase could enhance the autotrophic growth and biomass production of R. palustris. Microarray and real-time quantitative PCR revealed that transketolase isoforms I and II were involved in different carbon metabolic pathways. In addition, immunogold staining demonstrated that the two transketolase isoforms had different spatial localizations: transketolase I was primarily associated with the intracytoplasmic membrane (ICM) but transketolase II was mostly distributed in the cytoplasm. Comparative proteomic analysis and network construction of transketolase over-expression and negative control (NC) strains revealed that protein folding, transcriptional regulation, amino acid transport and CBB cycle-associated carbon metabolism were enriched in the transketolase I over-expressed strain. In contrast, ATP synthesis, carbohydrate transport, glycolysis-associated carbon metabolism and CBB cycle-associated carbon metabolism were enriched in the transketolase II over-expressed strain. Furthermore, ATP synthesis assays showed a significant increase in ATP synthesis in the transketolase II over-expressed strain. A PEPCK activity assay showed that PEPCK activity was higher in transketolase over-expressed strains than in the negative control strain.
  
  
  CONCLUSIONS
  Taken together, our results indicate that the two isoforms of transketolase in R. palustris could affect photoautotrophic growth through both common and divergent metabolic mechanisms.
authors.affiliation: Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.
authors.forename: Chia-Wei
authors.initials: CW
authors.lastname: Hu
authors.forename: Ya-Ling
authors.initials: YL
authors.lastname: Chang
authors.forename: Shiang Jiuun
authors.initials: SJ
authors.lastname: Chen
authors.forename: Ling-Long
authors.initials: LL
authors.lastname: Kuo-Huang
authors.forename: James C
authors.initials: JC
authors.lastname: Liao
authors.forename: Hsuan-Cheng
authors.initials: HC
authors.lastname: Huang
authors.forename: Hsueh-Fen
authors.initials: HF
authors.lastname: Juan
mesh_terms: D052818:Autotrophic Processes / Q000528:radiation effects; D001426:Bacterial Proteins / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D007527:Isoenzymes / Q000378:metabolism; D008027:Light; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000378:metabolism; D011485:Protein Binding / Q000528:radiation effects; D060066:Protein Interaction Maps / Q000528:radiation effects; D021381:Protein Transport / Q000528:radiation effects; D012241:Rhodopseudomonas / Q000201:enzymology* / Q000254:growth & development / Q000528:radiation effects; D013347:Subcellular Fractions / Q000201:enzymology / Q000528:radiation effects; D049490:Systems Biology / Q000379:methods*; D014174:Transketolase / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007527:Isoenzymes; D014174:Transketolase; D019764:Phosphoenolpyruvate Carboxykinase (ATP)