title: Distinct transcriptional regulation of the two Escherichia coli transhydrogenases PntAB and UdhA.
abstract: Transhydrogenases catalyse interconversion of the redox cofactors NADH and NADPH, thereby conveying metabolic flexibility to balance catabolic NADPH formation with anabolic or stress-based consumption of NADPH. Escherichia coli is one of the very few microbes that possesses two isoforms: the membrane-bound, proton-translocating transhydrogenase PntAB and the cytosolic, energy-independent transhydrogenase UdhA. Despite their physiological relevance, we have only fragmented information on their regulation and the signals coordinating their counteracting activities. Here we investigated PntAB and UdhA regulation by studying transcriptional responses to environmental and genetic perturbations. By testing pntAB and udhA GFP reporter constructs in the background of WT E. coli and 62 transcription factor mutants during growth on different carbon sources, we show distinct transcriptional regulation of the two transhydrogenase promoters. Surprisingly, transhydrogenase regulation was independent of the actual catabolic overproduction or underproduction of NADPH but responded to nutrient levels and growth rate in a fashion that matches the cellular need for the redox cofactors NADPH and/or NADH. Specifically, the identified transcription factors Lrp, ArgP and Crp link transhydrogenase expression to particular amino acids and intracellular concentrations of cAMP. The overall identified set of regulators establishes a primarily biosynthetic role for PntAB and link UdhA to respiration.
authors.affiliation: Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland.|Molecular Life Science Graduate School, Zurich, Switzerland.
authors.forename: Bart R B
authors.initials: BRB
authors.lastname: Haverkorn van Rijsewijk
authors.affiliation: Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland.|Systems Biology Graduate School, Zurich, Switzerland.
authors.forename: Karl
authors.initials: K
authors.lastname: Kochanowski
authors.affiliation: Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland.|Molecular Systems Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
authors.forename: Matthias
authors.initials: M
authors.lastname: Heinemann
authors.affiliation: Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland.
authors.forename: Uwe
authors.initials: U
authors.lastname: Sauer
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D009250:NADP Transhydrogenases / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; D014157:Transcription Factors; D009250:NADP Transhydrogenases; C556049:pntA protein, E coli; C556051:pntB protein, E coli