title: The Campylobacter jejuni RacRS two-component system activates the glutamate synthesis by directly upregulating γ-glutamyltranspeptidase (GGT).
abstract: The highly conserved enzyme γ-glutamyltranspeptidase (GGT) plays an important role in metabolism of glutathione and glutamine. Yet, the regulation of ggt transcription in prokaryotes is poorly understood. In the human pathogen Campylobacter jejuni, GGT is important as it contributes to persistent colonization of the gut. Here we show that the GGT activity in C. jejuni is dependent on a functional RacRS (reduced ability to colonize) two-component system. Electrophoretic mobility shift and luciferase reporter assays indicate that the response regulator RacR binds to a promoter region ~80 bp upstream of the ggt transcriptional start site, which contains a recently identified RacR DNA binding consensus sequence. RacR needs to be phosphorylated to activate the transcription of the ggt gene, which is the case under low oxygen conditions in presence of alternative electron acceptors. A functional GGT and RacR are needed to allow C. jejuni to grow optimally on glutamine as sole carbon source under RacR inducing conditions. However, when additional carbon sources are present C. jejuni is capable of utilizing glutamine independently of GGT. RacR is the first prokaryotic transcription factor known to directly up-regulate both the cytoplasmic [glutamine-2-oxoglutarate aminotransferase (GOGAT)] as well as the periplasmic (GGT) production of glutamate.
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Utrecht Netherlands.
authors.forename: Anne-Xander
authors.initials: AX
authors.lastname: van der Stel
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Utrecht Netherlands.
authors.forename: Andries
authors.initials: A
authors.lastname: van Mourik
authors.affiliation: Department of Bacterial Genetics, Institute of Microbiology, Faculty of Biology, University of Warsaw, Warsaw Poland.
authors.forename: Paweł
authors.initials: P
authors.lastname: Łaniewski
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Utrecht Netherlands.
authors.forename: Jos P M
authors.initials: JP
authors.lastname: van Putten
authors.affiliation: Department of Bacterial Genetics, Institute of Microbiology, Faculty of Biology, University of Warsaw, Warsaw Poland.
authors.forename: Elżbieta K
authors.initials: EK
authors.lastname: Jagusztyn-Krynicka
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Utrecht Netherlands.
authors.forename: Marc M S M
authors.initials: MM
authors.lastname: Wösten
keywords: Campylobacter jejuni; GGT; GOGAT; RacRS; gene regulation; glutamine-2-oxoglutarate aminotransferase; two-component system; γ-glutamyltranspeptidase