Regulatory Themes and Variations by the Stress-Signaling Nucleotide Alarmones (p)ppGpp in Bacteria

Annu Rev Genet. 2021 Aug 20. doi: 10.1146/annurev-genet-021821-025827. Online ahead of print.

Abstract

Bacterial stress-signaling alarmones are important components of a protective network against diverse stresses such as nutrient starvation and antibiotic assault. pppGpp and ppGpp, collectively (p)ppGpp, have well-documented regulatory roles in gene expression and protein translation. Recent work has highlighted another key function of (p)ppGpp: inducing rapid and coordinated changes in cellular metabolism by regulating enzymatic activities, especially those involved in purine nucleotide synthesis. Failure of metabolic regulation by (p)ppGpp results in the loss of coordination between metabolic and macromolecular processes, leading to cellular toxicity. In this review, we document how (p)ppGpp and newly characterized nucleotides pGpp and (p)ppApp directly regulate these enzymatic targets for metabolic remodeling. We examine targets' common determinants for alarmone interaction as well as their evolutionary diversification. We highlight classical and emerging themes in nucleotide signaling, including oligomerization and allostery along with metabolic interconversion and crosstalk, illustrating how they allow optimized bacterial adaptation to their environmental niches. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.