A network of acetyl phosphate-dependent modification modulates c-di-AMP homeostasis in Actinobacteria.

Cyclic purine nucleotides are important signal transduction molecules across all domains of life. 3',5'-cyclic di-adenosine monophosphate (c-di-AMP) has roles in both prokaryotes and eukaryotes, while the signals that adjust intracellular c-di-AMP and the molecular machinery enabling a network-wide homeostatic response remain largely unknown. Here, we present evidence for an acetyl phosphate (AcP)-governed network responsible for c-di-AMP homeostasis through two distinct substrates, the diadenylate cyclase DNA integrity scanning protein (DisA) and its newly identified transcriptional repressor, DasR. Correspondingly, we found that AcP-induced acetylation exerts these regulatory actions by disrupting protein multimerization, thus impairing c-di-AMP synthesis via K66 acetylation of DisA. Conversely, the transcriptional inhibition of disA was relieved during DasR acetylation at K78. These findings establish a pivotal physiological role for AcP as a mediator to balance c-di-AMP homeostasis. Further studies revealed that acetylated DisA and DasR undergo conformational changes that play crucial roles in differentiation. Considering the broad distribution of AcP-induced acetylation in response to environmental stress, as well as the high conservation of the identified key sites, we propose that this unique regulation of c-di-AMP homeostasis may constitute a fundamental property of central circuits in Actinobacteria and thus the global control of cellular physiology.IMPORTANCESince the identification of c-di-AMP is required for bacterial growth and cellular physiology, a major challenge is the cell signals and stimuli that feed into the decision-making process of c-di-AMP concentration and how that information is integrated into the regulatory pathways. Using the bacterium Saccharopolyspora erythraea as a model, we established that AcP-dependent acetylation of the diadenylate cyclase DisA and its newly identified transcriptional repressor DasR is involved in coordinating environmental and intracellular signals, which are crucial for c-di-AMP homeostasis. Specifically, DisA acetylated at K66 directly inactivates its diadenylate cyclase activity, hence the production of c-di-AMP, whereas DasR acetylation at K78 leads to increased disA expression and c-di-AMP levels. Thus, AcP represents an essential molecular switch in c-di-AMP maintenance, responding to environmental changes and possibly hampering efficient development. Therefore, AcP-mediated posttranslational processes constitute a network beyond the usual and well-characterized synthetase/hydrolase governing c-di-AMP homeostasis.

A meet-up of acetyl phosphate and c-di-GMP modulates BldD activity for development and antibiotic production.

Actinobacteria are ubiquitous bacteria undergoing complex developmental transitions coinciding with antibiotic production in response to stress or nutrient starvation. This transition is mainly controlled by the interaction between the second messenger c-di-GMP and the master repressor BldD. To date, the upstream factors and the global signal networks that regulate these intriguing cell biological processes remain unknown. In Saccharopolyspora erythraea, we found that acetyl phosphate (AcP) accumulation resulting from environmental nitrogen stress participated in the regulation of BldD activity through cooperation with c-di-GMP. AcP-induced acetylation of BldD at K11 caused the BldD dimer to fall apart and dissociate from the target DNA and disrupted the signal transduction of c-di-GMP, thus governing both developmental transition and antibiotic production. Additionally, practical mutation of BldDK11R bypassing acetylation regulation could enhance the positive effect of BldD on antibiotic production. The study of AcP-dependent acetylation is usually confined to the control of enzyme activity. Our finding represents an entirely different role of the covalent modification caused by AcP, which integrated with c-di-GMP signal in modulating the activity of BldD for development and antibiotic production, coping with environmental stress. This coherent regulatory network might be widespread across actinobacteria, thus has broad implications.