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.

Campylobacter jejuni CsrA Regulates Metabolic and Virulence Associated Proteins and Is Necessary for Mouse Colonization

“…AhpC transcription is not significantly affected by CosR knockdown, leading Hwang et al to conclude that AhpC is likely also regulated post-transcriptionally [ 40 ]; our present data suggests that this may be mediated by CsrA. RacR is a transcriptional regulator that controls the expression of a number of genes in response to growth temperature [ 41 – 43 ]. Although some of the RacR targets are also members of the CsrA regulon, including catalase, cytochrome c peroxidase, AnsA, AspA, Tlp6, and GGT [ 41 – 43 ], the majority are not.…”

“…RacR is a transcriptional regulator that controls the expression of a number of genes in response to growth temperature [ 41 – 43 ]. Although some of the RacR targets are also members of the CsrA regulon, including catalase, cytochrome c peroxidase, AnsA, AspA, Tlp6, and GGT [ 41 – 43 ], the majority are not. As with Fur, the lack of overlap among the majority of proteins in the CosR, RacR and CsrA regulons shows that CsrA effects are not manifest solely through CosR or RacR.…”

Catabolite repression in Campylobacter jejuni correlates with intracellular succinate levels

“…4A and data not shown). The two-component system RacRS has been shown to be a positive regulator of both gltB and ggt under oxygen-limiting conditions, especially when nitrate is available (van der Stel et al, 2015b). Because GGT activity is only dependent on RacR and not RacS, RacR might be cross-phosphorylated by otherhistidine kinases, or activated through high-energy phosphodonors like acetylphosphate under microaerobic conditions.…”

“…GGT activity was determined as described before (van der Stel et al, 2015b). GOGAT activity was measured by following the consumption of NADPH (Meers et al, 1970).…”

d-glutamate and Gut Microbiota in Alzheimer’s Disease

“…Moreover, they found that a lower abundance of two Campylobacter jejuni strains (81-176 and ICDCCJ07001) was associated with lower fumaric acid concentration in the guts of children with autism [35]. A previous study has shown that Campylobacter jejuni may activate glutamate synthesis [120]. Thus, lower abundance of Campylobacter jejuni may affect the synthesis of glutamate, which in turn would indirectly impact glutamate metabolism.…”