Unique Features of Alarmone Metabolism in Clostridioides difficile

Unique Features of Alarmone Metabolism in Clostridioides difficile

The "magic spot" alarmones (pp)pGpp, previously implicated in Clostridioides difficile antibiotic survival, are synthesized by the RelA-SpoT homolog (RSH) of C. difficile (RSH ) and RelQ . These enzymes are transcriptionally activated by diverse environmental stresses. RSH has previously b...

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Bibliographic Details
Published in:Journal of bacteriology Vol. 204; no. 4; p. e0057521
Main Authors: Poudel, Asia, Pokhrel, Astha, Oludiran, Adenrele, Coronado, Estevan J, Alleyne, Kwincy, Gilfus, Marrett M, Gurung, Raj K, Adhikari, Surya B, Purcell, Erin B
Format: Journal Article
Language:English
Published: United States American Society for Microbiology 19-04-2022
Subjects:
Anti-Bacterial Agents - pharmacology
Antibiotics
Bacterial Proteins - genetics
Bacterial Proteins - metabolism
Bacteriology
Cadmium
Clostridioides
Clostridioides difficile
Clostridium Infections
Editor's Pick
Environmental stress
Enzymes
Guanosine Pentaphosphate - metabolism
Homology
Humans
Hydrolysis
Ligases - metabolism
Metal ions
Metals
Phosphates
Research Article
Substrates
Synthesis
Transcription
Clostridioides difficile
(p)ppGpp
(pp)pGpp
alarmone
small alarm synthetase
stringent response
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Summary:The "magic spot" alarmones (pp)pGpp, previously implicated in Clostridioides difficile antibiotic survival, are synthesized by the RelA-SpoT homolog (RSH) of C. difficile (RSH ) and RelQ . These enzymes are transcriptionally activated by diverse environmental stresses. RSH has previously been reported to synthesize ppGpp, but in this study, we found that both clostridial enzymes exclusively synthesize pGpp. While direct synthesis of pGpp from a GMP substrate, and (p)ppGpp hydrolysis into pGpp by NUDIX hydrolases, have previously been reported, there is no precedent for a bacterium synthesizing pGpp exclusively. Hydrolysis of the 5' phosphate or pyrophosphate from GDP or GTP substrates is necessary for activity by the clostridial enzymes, neither of which can utilize GMP as a substrate. Both enzymes are remarkably insensitive to the size of their metal ion cofactor, tolerating a broad array of metals that do not allow activity in (pp)pGpp synthetases from other organisms. It is clear that while C. difficile utilizes alarmone signaling, its mechanisms of alarmone synthesis are not directly homologous to those in more completely characterized organisms. Despite the role of the stringent response in antibiotic survival and recurrent infections, it has been a challenging target for antibacterial therapies because it is so ubiquitous. This is an especially relevant consideration for the treatment of Clostridioides difficile infection (CDI), as exposure to broad-spectrum antibiotics that harm commensal microbes is a major risk factor for CDI. Here, we report that both of the alarmone synthetase enzymes that mediate the stringent response in this organism employ a unique mechanism that requires the hydrolysis of two phosphate bonds and synthesize the triphosphate alarmone pGpp exclusively. Inhibitors targeted against these noncanonical synthetases have the potential to be highly specific and minimize detrimental effects to stringent response pathways in commensal microbes.
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The authors declare no conflict of interest.
ISSN:0021-9193
1098-5530
DOI:10.1128/jb.00575-21