Mechanisms of Transcription Activation Exerted by GadX and GadW at the gadA and gadBC Gene Promoters of the Glutamate-Based Acid Resistance System in Escherichia coli

Abstract

In Escherichia coli the gad system protects the cell from the extreme acid stress encountered during transit through the host stomach. The structural genes gadA, gadB, and gadC encode two glutamate decarboxylase isoforms and a glutamate/␥-aminobutyrate (GABA) antiporter, respectively. Glutamate decarboxylation involves both proton consumption and production of GABA, a neutral compound which is finally exported via the GadC antiporter. Regulation of gadA and gadBC transcription is very complex, involving several circuits controlling expression under different growth phase, medium, and pH conditions. In this study we found that the AraC-like activators GadX and GadW share the same 44-bp binding sites in the gadA and gadBC regulatory regions. The common binding sites are centered at 110.5 bp and 220.5 bp upstream of the transcriptional start points of the gadA and gadBC genes, respectively. At the gadA promoter this regulatory element overlaps one of the binding sites of the repressor H-NS. The DNA of the gadBC promoter has an intrinsic bend which is centered at position ؊121. These findings, combined with transcriptional regulation studies, may account for the two different mechanisms of transcriptional activation by GadX and GadW at the two promoters studied. We speculate that while at the gadA promoter GadX and GadW activate transcription by displacing H-NS via an antirepressor mechanism, at the gadBC promoter the mechanism of activation involves looping of the DNA sequence between the promoter and the activator binding site.

Tricarboxylic Acid Cycle-Dependent Regulation of Staphylococcus epidermidis Polysaccharide Intercellular Adhesin Synthesis

“…Metabolic regulation was one of the first bacterial regulatory modalities identified, resulting in thousands of studies addressing all aspects of regulation. This long history of research into metabolic regulation has identified a large number of regulatory proteins capable of responding to changes in the intracellular concentrations of molecules associated with TCA cycle activity, such as NADH (e.g., Rex [4], NmrA [39], and CcpA [21]), citric acid (CcpC [30,33]), glutamate (GadX and GadW [75]), branched-chain amino acids (CodY [61]), and ATP (KinA [69]). These observations lead us to hypothesize that a regulatory protein or proteins respond to TCA cycle-associated metabolites and regulate icaADBC transcription and PIA synthesis.…”

New insights into transcriptional regulation by H-NS

“…Many examples of counter-silencing by DNA-binding proteins have been recently described. The AraC-like activators GadX and GadW promote gadA (glutamate decarboxylase) expression, important for acid stress resistance, by antagonizing H-NS [48]. Interestingly, the RNAP-associated protein SspA has been proposed to enhance cell survival at acid pH by reducing hns expression during stationary phase [49].…”

OmpR positively regulates urease expression to enhance acid survival of Yersinia pseudotuberculosis

“…In addition, many other genes which express metabolic enzymes, periplasmic proteins and regulators involved in AR in E. coli have also been examined by microarray and proteomic 2D-gel analyses (Blankenhorn et al, 1999;Tucker et al, 2002). Recently, the Lon protease, endoRNase RNase E and chaperone Hsp31 have been shown to be important in controlling AR systems in E. coli (Heuveling et al, 2008;Mujacic & Baneyx, 2007;Takada et al, 2007), and the roles of AraC-family regulators GadX and GadW and the multidrug resistance regulator MarA in AR systems have also been investigated (Ruiz et al, 2008;Sayed et al, 2007;Tramonti et al, 2006). Nevertheless, despite advances in unravelling some of the regulatory networks involved in AR systems (Foster, 2004;Masuda & Church, 2003), it remains unclear how these factors function together to promote cell survival in low pH conditions.…”