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The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

ABSTRACT: Bacteria synthesize guanosine tetra- and penta phosphate (commonly referred to as (p)ppGpp) in response to environmental stresses. (p)ppGpp reprograms cell physiology and is essential for stress survival, virulence and antibiotic tolerance. Proteins of the RSH superfamily (RelA/SpoT Homologues) are ubiquitously distributed and hydrolyze or synthesize (p)ppGpp. Structural studies have suggested that the shift between hydrolysis and synthesis is governed by conformational antagonism between the two active sites in RSHs. RelA proteins of γ-proteobacteria exclusively synthesize (p)ppGpp and encode an inactive pseudo-hydrolase domain. Escherichia coli RelA synthesizes (p)ppGpp in response to amino acid starvation with cognate uncharged tRNA at the ribosomal A-site, however, mechanistic details to the regulation of the enzymatic activity on the ribosome remain elusive. Here, we show a novel role of the enzymatically inactive hydrolase domain in modulating the activity of the synthetase domain of RelA. Using random mutagenesis screening and functional studies, we identify a loop region (residues 114-130) in the hydrolase domain, which controls the synthetase activity. We show that a synthetase-inactive loop mutant of RelA is not affected for tRNA binding, but binds the ribosome less efficiently than wildtype RelA. Our data provide strong evidence to support the model that the hydrolase domain acts as a molecular switch to regulate the synthetase activity.

ORGANISM(S): Escherichia coli

PROVIDER: GSE150416 | GEO | 2021/03/31

REPOSITORIES: GEO

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Activation of the stringent response by loading of tRNA-RelA complexes at the ribosomal A-site

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The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

Project description:The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

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Regulation of the stringent response is the essential function of the conserved bacterial G protein CgtA in V. cholerae

Project description:The gene encoding the conserved bacterial G protein CgtA (Obg) is essential for viability in every organism in which it has been studied. CgtA has been reported to be involved in several diverse bacterial functions, including ribosome assembly, DNA repair, sporulation and morphological development. However, none of these functions have been identified as essential. Here we show that depletion of CgtA in Vibrio cholerae causes global changes in gene expression that are consistent with induction of a classical low nutrient stress response or “stringent” response. We show that depletion of CgtA leads to increased ppGpp levels which correlates with induction of the global stress response and cessation of growth. The enzyme RelA is responsible for synthesis of the alarmone ppGpp during the stringent response. We show that CgtA is no longer essential in a relA deletion mutant and thus conclude that the essentiality of CgtA is directly linked to its ability to affect ppGpp levels. The enzyme SpoT degrades ppGpp and here we show that SpoT is essential in a RelA+ CgtA+ background but not in a relA deletion mutant. We also confirmed that CgtA interacts with SpoT in a two-hybrid assay. We suggest that the essential function of CgtA is a repressor of the stringent response, and acts by regulating SpoT activity to maintain low ppGpp levels when bacteria are growing in a nutrient rich environment. This SuperSeries is composed of the SubSeries listed below.

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