• More than just a metabolic regulator--elucidation and validation of new targets of PdhR in Escherichia coli.

      Göhler, Anna-Katharina; Kökpinar, Öznur; Schmidt-Heck, Wolfgang; Geffers, Robert; Guthke, Reinhard; Rinas, Ursula; Schuster, Stefan; Jahreis, Knut; Kaleta, Christoph; Department of Genetics, University of Osnabrück, Osnabrück, Germany. (2011)
      The pyruvate dehydrogenase regulator protein (PdhR) of Escherichia coli acts as a transcriptional regulator in a pyruvate dependent manner to control central metabolic fluxes. However, the complete PdhR regulon has not yet been uncovered. To achieve an extended understanding of its gene regulatory network, we combined large-scale network inference and experimental verification of results obtained by a systems biology approach.
    • Mutation in a "tesB-like" hydroxyacyl-coenzyme A-specific thioesterase gene causes hyperproduction of extracellular polyhydroxyalkanoates by Alcanivorax borkumensis SK2.

      Sabirova, Julia S; Ferrer, Manuel; Lünsdorf, Heinrich; Wray, Victor; Kalscheuer, Rainer; Steinbüchel, Alexander; Timmis, Kenneth N; Golyshin, Peter N; Department of Environmental Microbiology, HZI-Helmholtz Center fro Infection Research, Braunschweig, Germany. jsa05@helmholtz-hzi.de (2006-12)
      A novel mutant of the marine oil-degrading bacterium Alcanivorax borkumensis SK2, containing a mini-Tn5 transposon disrupting a "tesB-like" acyl-coenzyme A (CoA) thioesterase gene, was found to hyperproduce polyhydroxyalkanoates (PHA), resulting in the extracellular deposition of this biotechnologically important polymer when grown on alkanes. The tesB-like gene encodes a distinct novel enzyme activity, which acts exclusively on hydroxylated acyl-CoAs and thus represents a hydroxyacyl-CoA-specific thioesterase. Inactivation of this enzyme results in the rechanneling of CoA-activated hydroxylated fatty acids, the cellular intermediates of alkane degradation, towards PHA production. These findings may open up new avenues for the development of simplified biotechnological processes for the production of PHA as a raw material for the production of bioplastics.
    • The 'pH optimum anomaly' of intracellular enzymes of Ferroplasma acidiphilum.

      Golyshina, Olga V; Golyshin, Peter N; Timmis, Kenneth N; Ferrer, Manuel; Division of Microbiology, GBF--German Research Centre for Biotechnology, Braunschweig, Germany. (2006-03)
      A wide range of microorganisms, the so-called acidophiles, inhabit acidic environments and grow optimally at pH values between 0 and 3. The intracellular pH of these organisms is, however, close to neutrality or slightly acidic. It is to be expected that enzymatic activities dedicated to extracellular functions would be adapted to the prevailing low pH of the environment (0-3), whereas intracellular enzymes would be optimally active at the near-neutral pH of the cytoplasm (4.6-7.0). The genes of several intracellular or cell-bound enzymes, a carboxylesterase and three alpha-glucosidases, from Ferroplasma acidiphilum, a cell wall-lacking acidophilic archaeon with a growth optimum at pH 1.7, were cloned and expressed in Escherichia coli, and their products purified and characterized. The Ferroplasmaalpha-glucosidases exhibited no sequence similarity to known glycosyl hydrolases. All enzymes functioned and were stable in vitro in the pH range 1.7-4.0, and had pH optima much lower than the mean intracellular pH of 5.6. This 'pH optimum anomaly' suggests the existence of yet-undetected cellular compartmentalization providing cytoplasmic pH patchiness and low pH environments for the enzymes we have analysed.
    • Recombinant protein production associated growth inhibition results mainly from transcription and not from translation.

      Li, Zhaopeng; Rinas, Ursula; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (BMC (part of Springer), 2020-04-06)
      Background: Recombinant protein production can be stressful to the host organism. The extent of stress is determined by the specific properties of the recombinant transcript and protein, by the rates of transcription and translation, and by the environmental conditions encountered during the production process. Results: The impact of the transcription of the T7-promoter controlled genes encoding human basic fibroblast growth factor (hFGF-2) and green fluorescent protein (GFP) as well as the translation into the recombinant protein on the growth properties of the production host E. coli BL21(DE3) were investigated. This was done by using expression vectors where the promoter region or the ribosome binding site(s) or both were removed. It is shown that already transcription without protein translation imposes a metabolic burden on the host cell. Translation of the transcript into large amounts of a properly folded protein does not show any effect on cell growth in the best case, e.g. high-level production of GFP in Luria-Bertani medium. However, translation appears to contribute to the metabolic burden if it is connected to protein folding associated problems, e.g. inclusion body formation. Conclusion: The so-called metabolic burden of recombinant protein production is mainly attributed to transcription but can be enhanced through translation and those processes following translation (e.g. protein folding and degradation, heat-shock responses).
    • Recombinant protein production-associated metabolic burden reflects anabolic constraints and reveals similarities to a carbon overfeeding response.

      Li, Zhaopeng; Rinas, Ursula; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (Wiley, 2020-09-03)
      A comparison of the metabolic response of Escherichia coli BL21 (DE3) towards the production of human basic fibroblast growth factor (hFGF-2) or towards carbon overfeeding revealed similarities which point to constraints in anabolic pathways. Contrary to expectations, neither energy generation (e.g., ATP) nor provision of precursor molecules for nucleotides (e.g., uracil) and amino acids (e.g., pyruvate, glutamate) limit host cell and plasmid-encoded functions. Growth inhibition is assumed to occur when hampered anabolic capacities do not match with the ongoing and overwhelming carbon catabolism. Excessive carbon uptake leads to by-product secretion, for example, pyruvate, acetate, glutamate, and energy spillage, for example, accumulation and degradation of adenine nucleotides with concomitant accumulation of extracellular hypoxanthine. The cellular response towards compromised anabolic capacities involves downregulation of cAMP formation, presumably responsible for subsequently better-controlled glucose uptake and resultant accumulation of glucose in the culture medium. Growth inhibition is neglectable under conditions of reduced carbon availability when hampered anabolic capacities also match with catabolic carbon processing. The growth inhibitory effect with accompanying energy spillage, respectively, hypoxanthine secretion and cessation of cAMP formation is not unique to the production of hFGF-2 but observed during the production of other proteins and also during overexpression of genes without transcript translation.