Replacement of oxygen with sulfur on the furanose ring of cyclic dinucleotides enhances the immunostimulatory effect via STING activation

The cyclic dinucleotides cyclic 3′,5′-diguanylate (c-di-GMP) and cyclic 3′,5′-diadenylate (c-di-AMP) have emerged as key components of bacterial signal transduction networks. These closely related second messengers follow the classical general principles of nucleotide signaling by integrating diverse signals into regulatory pathways that control cellular responses to changing environments. They impact distinct cellular processes, with c-di-GMP having an established role in promoting bacterial adhesion and inhibiting motility and c-di-AMP being involved in cell wall metabolism, potassium homeostasis, and DNA repair. The involvement of c-dinucleotides in the physiology of the filamentous, nonmotile streptomycetes remained obscure until recent discoveries showed that c-di-GMP controls the activity of the developmental master regulator BldD and that c-di-AMP determines the level of the resuscitation-promoting factor A(RpfA) cell wall-remodelling enzyme. Here, I summarize our current knowledge of c-dinucleotide signaling inStreptomycesspecies and highlight the important roles of c-di-GMP and c-di-AMP in the biology of these antibiotic-producing, multicellular bacteria.

Download Full-text

Progress in Understanding the Molecular Basis Underlying Functional Diversification of Cyclic Dinucleotide Turnover Proteins

Journal of Bacteriology ◽

10.1128/jb.00790-16 ◽

2016 ◽

Vol 199 (5) ◽

Cited By ~ 22

Author(s):

Ute Römling ◽

Zhao-Xun Liang ◽

J. Maxwell Dow

Keyword(s):

Molecular Basis ◽

Current Knowledge ◽

Second Messenger ◽

Diguanylate Cyclase ◽

Structural Variations ◽

Functional Diversification ◽

Cyclic Dinucleotides ◽

Signaling Domains ◽

Synthesis And Degradation ◽

Cyclic Dinucleotide

ABSTRACT Cyclic di-GMP was the first cyclic dinucleotide second messenger described, presaging the discovery of additional cyclic dinucleotide messengers in bacteria and eukaryotes. The GGDEF diguanylate cyclase (DGC) and EAL and HD-GYP phosphodiesterase (PDE) domains conduct the turnover of cyclic di-GMP. These three unrelated domains belong to superfamilies that exhibit significant variations in function, and they include both enzymatically active and inactive members, with a subset involved in synthesis and degradation of other cyclic dinucleotides. Here, we summarize current knowledge of sequence and structural variations that underpin the functional diversification of cyclic di-GMP turnover proteins. Moreover, we highlight that superfamily diversification is not restricted to cyclic di-GMP signaling domains, as particular DHH/DHHA1 domain and HD domain proteins have been shown to act as cyclic di-AMP phosphodiesterases. We conclude with a consideration of the current limitations that such diversity of action places on bioinformatic prediction of the roles of GGDEF, EAL, and HD-GYP domain proteins.

Download Full-text

STING mediates immune responses in the closest living relatives of animals

eLife ◽

10.7554/elife.70436 ◽

2021 ◽

Vol 10 ◽

Author(s):

Arielle Woznica ◽

Ashwani Kumar ◽

Carolyn R Sturge ◽

Chao Xing ◽

Nicole King ◽

...

Keyword(s):

Immune Responses ◽

Model System ◽

Innate Immune ◽

Dependent Manner ◽

First Line ◽

Immune Genes ◽

Cyclic Dinucleotides ◽

Immune Pathways ◽

Innate Immune Genes ◽

Cyclic Dinucleotide

Animals have evolved unique repertoires of innate immune genes and pathways that provide their first line of defense against pathogens. To reconstruct the ancestry of animal innate immunity, we have developed the choanoflagellate Monosiga brevicollis, one of the closest living relatives of animals, as a model for studying mechanisms underlying pathogen recognition and immune response. We found that M. brevicollis is killed by exposure to Pseudomonas aeruginosa bacteria. Moreover, M. brevicollis expresses STING, which, in animals, activates innate immune pathways in response to cyclic dinucleotides during pathogen sensing. M. brevicollis STING increases the susceptibility of M. brevicollis to P. aeruginosa-induced cell death and is required for responding to the cyclic dinucleotide 2'3' cGAMP. Furthermore, similar to animals, autophagic signaling in M. brevicollis is induced by 2'3' cGAMP in a STING-dependent manner. This study provides evidence for a pre-animal role for STING in antibacterial immunity and establishes M. brevicollis as a model system for the study of immune responses.

Download Full-text

NrnA is a linear dinucleotide phosphodiesterase with limited function in cyclic dinucleotide metabolism in Listeria monocytogenes

Journal of Bacteriology ◽

10.1128/jb.00206-21 ◽

2021 ◽

Author(s):

Aaron R. Gall ◽

Brian Y. Hsueh ◽

Cheta Siletti ◽

Christopher M. Waters ◽

TuAnh N. Huynh

Keyword(s):

Listeria Monocytogenes ◽

Mammalian Cells ◽

Cell Infection ◽

Cellular Processes ◽

Hydrolytic Activities ◽

Limited Function ◽

Cyclic Dinucleotides ◽

Virulence Regulator ◽

Cyclic Dinucleotide

Listeria monocytogenes produces both c-di-AMP and c-di-GMP to mediate many important cellular processes, but the levels of both nucleotides must be regulated. C-di-AMP accumulation attenuates virulence and diminishes stress response, and c-di-GMP accumulation impairs bacterial motility. An important regulatory mechanism to maintain c-di-AMP and c-di-GMP homeostasis is to hydrolyze them to the linear dinucleotides pApA and pGpG, respectively, but the fates of these hydrolytic products have not been examined in L. monocytogenes . We found that NrnA, a stand-alone DHH-DHHA1 phosphodiesterase, has a broad substrate range, but with a strong preference for linear dinucleotides over cyclic dinucleotides. Although NrnA exhibited detectable cyclic dinucleotide hydrolytic activities in vitro, NrnA had negligible effects on their levels in the bacterial cell, even in the absence of the c-di-AMP phosphodiesterases PdeA and PgpH. The Δ nrnA mutant had a mammalian cell infection defect that was fully restored by E. coli Orn. Together, our data indicate that L. monocytogenes NrnA is functionally orthologous to Orn, and its preferred physiological substrates are most likely linear dinucleotides. Furthermore, our findings revealed that, unlike some other c-di-AMP and c-di-GMP-producing bacteria, L. monocytogenes does not employ their hydrolytic products to regulate their phosphodiesterases, at least at the pApA and pGpG levels in the Δ nrnA mutant. Finally, the Δ nrnA infection defect was overcome by constitutive activation of PrfA, the master virulence regulator, suggesting that accumulated linear dinucleotides might inhibit the expression, stability, or function of PrfA-regulated virulence factors. IMPORTANCE Listeria monocytogenes produces both c-di-AMP and c-di-GMP, and encodes specific phosphodiesterases that degrade them into pApA and pGpG, respectively, but the metabolism of these products has not been characterized in this bacterium. We found that L. monocytogenes NrnA degrades a broad range of nucleotides. Among the tested cyclic and linear substrates, it exhibits a strong biochemical and physiological preference the linear dinucleotides pApA, pGpG, and pApG. Unlike in some other bacteria, these oligoribonucleotides do not appear to interfere with cyclic dinucleotide hydrolysis. The absence of NrnA is well tolerated by L. monocytogenes in broth cultures but impairs its ability to infect mammalian cells. These findings indicate a separation of cyclic dinucleotide signaling and oligoribonucleotide metabolism in L. monocytogenes .

Download Full-text

The Age of Cyclic Dinucleotide Vaccine Adjuvants

Vaccines ◽

10.3390/vaccines8030453 ◽

2020 ◽

Vol 8 (3) ◽

pp. 453

Author(s):

Himanshu Gogoi ◽

Samira Mansouri ◽

Lei Jin

Keyword(s):

Vaccine Development ◽

Cytotoxic T Cells ◽

Prophylactic Vaccine ◽

Vaccine Adjuvants ◽

Therapeutic Cancer Vaccine ◽

Durable Regression ◽

The Status ◽

Cyclic Dinucleotides ◽

Cyclic Dinucleotide

As prophylactic vaccine adjuvants for infectious diseases, cyclic dinucleotides (CDNs) induce safe, potent, long-lasting humoral and cellular memory responses in the systemic and mucosal compartments. As therapeutic cancer vaccine adjuvants, CDNs induce potent anti-tumor immunity, including cytotoxic T cells and NK cells activation that achieve durable regression in multiple mouse models of tumors. Clinical trials are ongoing to fulfill the promise of CDNs (ClinicalTrials.gov: NCT02675439, NCT03010176, NCT03172936, and NCT03937141). However, in October 2018, the first clinical data with Merck’s CDN MK-1454 showed zero activity as a monotherapy in patients with solid tumors or lymphomas (NCT03010176). Lately, the clinical trial from Aduro’s CDN ADU-S100 monotherapy was also disappointing (NCT03172936). The emerging hurdle in CDN vaccine development calls for a timely re-evaluation of our understanding on CDN vaccine adjuvants. Here, we review the status of CDN vaccine adjuvant research, including their superior adjuvant activities, in vivo mode of action, and confounding factors that affect their efficacy in humans. Lastly, we discuss the strategies to overcome the hurdle and advance promising CDN adjuvants in humans.

Download Full-text

STING mediates immune responses in a unicellular choanoflagellate

10.1101/2021.05.13.443778 ◽

2021 ◽

Author(s):

Arielle Woznica ◽

Ashwani Kumar ◽

Carolyn R Sturge ◽

Chao Xing ◽

Nicole King ◽

...

Keyword(s):

Immune Responses ◽

Model System ◽

Innate Immune ◽

Dependent Manner ◽

First Line ◽

Immune Genes ◽

Cyclic Dinucleotides ◽

Immune Pathways ◽

Innate Immune Genes ◽

Cyclic Dinucleotide

Animals have evolved unique repertoires of innate immune genes and pathways that provide their first line of defense against pathogens. To reconstruct the ancestry of animal innate immunity, we have developed the choanoflagellate Monosiga brevicollis, one of the closest living relatives of animals, as a model for studying mechanisms underlying pathogen recognition and immune response. We found that M. brevicollis is killed by exposure to Pseudomonas aeruginosa bacteria and selectively avoids ingesting them. Moreover, M. brevicollis expresses STING, which, in animals, activates innate immune pathways in response to cyclic dinucleotides during pathogen sensing. M. brevicollis STING increases the susceptibility of M. brevicollis to P. aeruginosa-induced cell death and is required for responding to the cyclic dinucleotide 2'3' cGAMP. Furthermore, similar to animals, autophagic signaling in M. brevicollis is induced by 2'3' cGAMP in a STING-dependent manner. This study provides evidence for a pre-animal role for STING in antibacterial immunity and establishes M. brevicollis as a model system for the study of immune responses.

Download Full-text

Hybrid promiscuous (Hypr) GGDEF enzymes produce cyclic AMP-GMP (3′, 3′-cGAMP)

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1515287113 ◽

2016 ◽

Vol 113 (7) ◽

pp. 1790-1795 ◽

Cited By ~ 45

Author(s):

Zachary F. Hallberg ◽

Xin C. Wang ◽

Todd A. Wright ◽

Beiyan Nan ◽

Omer Ad ◽

...

Keyword(s):

Cyclic Amp ◽

Predictive Power ◽

Geobacter Sulfurreducens ◽

Bacterial Genomes ◽

Diguanylate Cyclases ◽

Genes Encoding ◽

Cyclic Dinucleotides ◽

Ggdef Domain ◽

Cyclic Dinucleotide

Over 30 years ago, GGDEF domain-containing enzymes were shown to be diguanylate cyclases that produce cyclic di-GMP (cdiG), a second messenger that modulates the key bacterial lifestyle transition from a motile to sessile biofilm-forming state. Since then, the ubiquity of genes encoding GGDEF proteins in bacterial genomes has established the dominance of cdiG signaling in bacteria. However, the observation that proteobacteria encode a large number of GGDEF proteins, nearing 1% of coding sequences in some cases, raises the question of why bacteria need so many GGDEF enzymes. In this study, we reveal that a subfamily of GGDEF enzymes synthesizes the asymmetric signaling molecule cyclic AMP-GMP (cAG or 3′, 3′-cGAMP). This discovery is unexpected because GGDEF enzymes function as symmetric homodimers, with each monomer binding to one substrate NTP. Detailed analysis of the enzyme from Geobacter sulfurreducens showed it is a dinucleotide cyclase capable of switching the major cyclic dinucleotide (CDN) produced based on ATP-to-GTP ratios. We then establish through bioinformatics and activity assays that hybrid CDN-producing and promiscuous substrate-binding (Hypr) GGDEF enzymes are found in other deltaproteobacteria. Finally, we validated the predictive power of our analysis by showing that cAG is present in surface-grown Myxococcus xanthus. This study reveals that GGDEF enzymes make alternative cyclic dinucleotides to cdiG and expands the role of this widely distributed enzyme family to include regulation of cAG signaling.

Download Full-text

NrnA is a linear dinucleotide phosphodiesterase with limited function in cyclic dinucleotide metabolism in Listeria monocytogenes

10.1101/2021.04.21.440870 ◽

2021 ◽

Author(s):

Aaron R. Gall ◽

Cheta Siletti ◽

TuAnh N. Huynh

Keyword(s):

Listeria Monocytogenes ◽

Mammalian Cells ◽

Cell Infection ◽

Cellular Processes ◽

Hydrolytic Activities ◽

Limited Function ◽

Cyclic Dinucleotides ◽

Virulence Regulator ◽

Cyclic Dinucleotide

ABSTRACTListeria monocytogenes produces both c-di-AMP and c-di-GMP to mediate many important cellular processes, but the levels of both nucleotides must be regulated. C-di-AMP accumulation attenuates virulence and diminishes stress response, and c-di-GMP accumulation impairs bacterial motility. An important regulatory mechanism to maintain c-di-AMP and c-di-GMP homeostasis is to hydrolyze them to the linear dinucleotides pApA and pGpG, respectively, but the fates of these hydrolytic products have not been examined in L. monocytogenes. We found that NrnA, a stand-alone DHH-DHHA1 phosphodiesterase, has a broad substrate range, but with a strong preference for linear dinucleotides over cyclic dinucleotides. Although NrnA exhibited detectable cyclic dinucleotide hydrolytic activities in vitro, NrnA had negligible effects on their levels in the bacterial cell, even in the absence of the c-di-AMP phosphodiesterases PdeA and PgpH. The ΔnrnA mutant had a mammalian cell infection defect that was fully restored by E. coli Orn. Together, our data indicate that L. monocytogenes NrnA is functionally orthologous to Orn, and its preferred physiological substrates are most likely linear dinucleotides. Furthermore, our findings revealed that, unlike some other c-di-AMP and c-di-GMP-producing bacteria, L. monocytogenes does not employ their hydrolytic products to regulate their phosphodiesterases, at least at the pApA and pGpG levels in the ΔnrnA mutant. Finally, the ΔnrnA infection defect was overcome by constitutive activation of PrfA, the master virulence regulator, suggesting that accumulated linear dinucleotides might inhibit the expression, stability, or function of PrfA-regulated virulence factors.IMPORTANCEListeria monocytogenes produces both c-di-AMP and c-di-GMP, and encodes specific phosphodiesterases that degrade them into pApA and pGpG, respectively, but the metabolism of these products has not been characterized in this bacterium. We found that L. monocytogenes harbors an NrnA homolog that degrades a broad range of nucleotides, but exhibits a strong biochemical and physiological preference for linear dinucleotides, including pApA and pGpG. Unlike in some other bacteria, these oligoribonucleotides do not appear to interfere with cyclic dinucleotide hydrolysis. The absence of NrnA is well tolerated by L. monocytogenes in broth cultures but impairs its ability to infect mammalian cells. These findings indicate a separation of cyclic dinucleotide signaling and oligoribonucleotide metabolism in L. monocytogenes.

Download Full-text

Structures of c-di-GMP/cGAMP degrading phosphodiesterase VcEAL: identification of a novel conformational switch and its implication

Biochemical Journal ◽

10.1042/bcj20190399 ◽

2019 ◽

Vol 476 (21) ◽

pp. 3333-3353 ◽

Cited By ~ 3

Author(s):

Malti Yadav ◽

Kamalendu Pal ◽

Udayaditya Sen

Keyword(s):

Active Site ◽

Metal Binding ◽

Metal Ion ◽

Triosephosphate Isomerase ◽

Catalytic Mechanism ◽

Degradation Mechanism ◽

Structural Basis ◽

Conserved Residues ◽

Phosphodiester Bond ◽

Cyclic Dinucleotides

Cyclic dinucleotides (CDNs) have emerged as the central molecules that aid bacteria to adapt and thrive in changing environmental conditions. Therefore, tight regulation of intracellular CDN concentration by counteracting the action of dinucleotide cyclases and phosphodiesterases (PDEs) is critical. Here, we demonstrate that a putative stand-alone EAL domain PDE from Vibrio cholerae (VcEAL) is capable to degrade both the second messenger c-di-GMP and hybrid 3′3′-cyclic GMP–AMP (cGAMP). To unveil their degradation mechanism, we have determined high-resolution crystal structures of VcEAL with Ca2+, c-di-GMP-Ca2+, 5′-pGpG-Ca2+ and cGAMP-Ca2+, the latter provides the first structural basis of cGAMP hydrolysis. Structural studies reveal a typical triosephosphate isomerase barrel-fold with substrate c-di-GMP/cGAMP bound in an extended conformation. Highly conserved residues specifically bind the guanine base of c-di-GMP/cGAMP in the G2 site while the semi-conserved nature of residues at the G1 site could act as a specificity determinant. Two metal ions, co-ordinated with six stubbornly conserved residues and two non-bridging scissile phosphate oxygens of c-di-GMP/cGAMP, activate a water molecule for an in-line attack on the phosphodiester bond, supporting two-metal ion-based catalytic mechanism. PDE activity and biofilm assays of several prudently designed mutants collectively demonstrate that VcEAL active site is charge and size optimized. Intriguingly, in VcEAL-5′-pGpG-Ca2+ structure, β5–α5 loop adopts a novel conformation that along with conserved E131 creates a new metal-binding site. This novel conformation along with several subtle changes in the active site designate VcEAL-5′-pGpG-Ca2+ structure quite different from other 5′-pGpG bound structures reported earlier.

Download Full-text

Unraveling cGAS catalytic mechanism upon DNA activation through molecular dynamics simulations

Physical Chemistry Chemical Physics ◽

10.1039/d1cp00378j ◽

2021 ◽

Author(s):

Jordi Soler ◽

Pedro Paiva ◽

Maria Joao Joao Ramos ◽

Pedro Alexandrino Fernandes ◽

Marie Brut

Keyword(s):

Molecular Dynamics ◽

Dna Binding ◽

Molecular Dynamics Simulations ◽

Cyclic Gmp ◽

Catalytic Mechanism ◽

System P ◽

Dynamics Simulations ◽

Cyclic Dinucleotide

Cyclic GMP-AMP Synthase (cGAS) is activated upon DNA binding and catalyzes the synthesis of 2’,3’-cGAMP from GTP and ATP. This cyclic dinucleotide is a messenger that triggers the autoimmune system...

Download Full-text