bis(3--5-)-cyclic-diguanylic-acid and cyclic-diadenosine-phosphate

The regulation of multiple bacterial phenotypes was found to depend on different cyclic dinucleotides (CDNs) that constitute intracellular signaling second messenger systems. Most notably, c-di-GMP, along with proteins related to its synthesis, sensing, and degradation, was identified as playing a central role in the switching from biofilm to planktonic modes of growth. Recently, this research topic has been under expansion, with the discoveries of new CDNs, novel classes of CDN receptors, and the numerous functions regulated by these molecules. In this review, we comprehensively describe the three main bacterial enzymes involved in the synthesis of c-di-GMP, c-di-AMP, and cGAMP focusing on description of their three-dimensional structures and their structural similarities with other protein families, as well as the essential residues for catalysis. The diversity of CDN receptors is described in detail along with the residues important for the interaction with the ligand. Interestingly, genomic data strongly suggest that there is a tendency for bacterial cells to use both c-di-AMP and c-di-GMP signaling networks simultaneously, raising the question of whether there is crosstalk between different signaling systems. In summary, the large amount of sequence and structural data available allows a broad view of the complexity and the importance of these CDNs in the regulation of different bacterial behaviors. Nevertheless, how cells coordinate the different CDN signaling networks to ensure adaptation to changing environmental conditions is still open for much further exploration.

Topics: Bacteria; Bacterial Proteins; Binding Sites; Biofilms; Cyclic GMP; Dinucleoside Phosphates; Gene Expression Regulation, Bacterial; Models, Molecular; Nucleotides, Cyclic; Plankton; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Signal Transduction

Since the discovery of cyclic dimeric guanosine 3',5'-monophosphate (c-di-GMP) in 1987, the role of cyclic dinucleotides in signal pathways has been extensively studied. Many receptors and effectors of cyclic dinucleotides have been identified which play important roles in cellular processes. Example of such effectors include cyclic dimeric adenosine 3',5'-monophosphate (c-di-AMP)-binding proteins and endoplasmic reticulum membrane adaptor. Accumulating evidence indicate that cyclic dinucleotides act as second messengers that not only regulate the bacterial physiological processes but also affect host immune responses during infections. Streptococci species, which produce cyclic dinucleotides, are responsible for many human diseases. Numerous studies suggest that the cyclic dinucleotides are vital in signal transduction pathways as second messengers and influence the progression of infectious diseases. Here, we provide an overview of the molecular principles of cyclic dinucleotides synthesis and degradation and discuss recent progress on streptococcal signal transduction pathways by cyclic dinucleotide second messengers and their role in regulating host immune reaction. This review will provide a better understanding of the molecular mechanisms of streptococcal cyclic dinucleotide second messengers thereby revealing novel targets for preventing infections.

Topics: Bacterial Adhesion; Bacterial Proteins; Carrier Proteins; Cyclic AMP Response Element-Binding Protein; Cyclic GMP; Dinucleoside Phosphates; Gene Expression Regulation, Bacterial; Host-Pathogen Interactions; Humans; Intracellular Signaling Peptides and Proteins; Phenotype; Second Messenger Systems; Streptococcal Infections; Streptococcus pneumoniae; Streptococcus pyogenes; Virulence

A biofilm is a complex assemblage of microbial communities adhered to a biotic or an abiotic surface which is embedded within a self-produced matrix of extracellular polymeric substances. Many transcriptional regulators play a role in triggering a motile-sessile switch and in consequently producing the biofilm matrix. This review is aimed at highlighting the role of two nucleotide signaling molecules (c-di-GMP and c-di-AMP), toxin antitoxin modules and a novel transcriptional regulator BolA in biofilm formation in various bacteria. In addition, it highlights the common themes that have appeared in recent research regarding the key regulatory components and signal transduction pathways that help Bacillus subtilis and Pseudomonas aeruginosa to acquire the biofilm mode of life.

Topics: Bacillus subtilis; Biofilms; Cyclic GMP; Dinucleoside Phosphates; Extracellular Matrix; Gene Expression Regulation, Bacterial; Pseudomonas aeruginosa; Signal Transduction

Cyclic dinucleotides (CDNs) are highly versatile signalling molecules that control various important biological processes in bacteria. The best-studied example is cyclic di-GMP (c-di-GMP). Known since the late 1980s, it is now recognized as a near-ubiquitous second messenger that coordinates diverse aspects of bacterial growth and behaviour, including motility, virulence, biofilm formation and cell cycle progression. In this Review, we discuss important new insights that have been gained into the molecular principles of c-di-GMP synthesis and degradation, which are mediated by diguanylate cyclases and c-di-GMP-specific phosphodiesterases, respectively, and the cellular functions that are exerted by c-di-GMP-binding effectors and their diverse targets. Finally, we provide a short overview of the signalling versatility of other CDNs, including c-di-AMP and cGMP-AMP (cGAMP).

Topics: Bacteria; Biofilms; Cyclic GMP; Dinucleoside Phosphates; Gene Expression Regulation, Bacterial; Nucleotides, Cyclic; Second Messenger Systems; Signal Transduction

Signal sensing in bacteria has traditionally been attributed to protein-based factors. It is however becoming increasingly clear that bacteria also exploit RNAs to serve this role. This review discusses how key developmental processes in bacteria, such as community formation, choice of a sessile versus motile lifestyle, or vegetative growth versus dormant spore formation may be governed by signal sensing RNAs. The signaling molecules that affect these processes, the RNAs that sense these molecules and the underlying molecular basis for specific signal-response are discussed here.

Topics: Bacteria; Binding Sites; Cyclic GMP; Dinucleoside Phosphates; Molecular Structure; Nucleic Acid Conformation; Riboswitch; RNA, Bacterial; Second Messenger Systems; Signal Transduction

Cyclic (c-di-GMP) is the prevalent intracellular signaling intermediate in bacteria. It triggers a spectrum of responses that cause bacteria to shift from a swarming motile phase to sessile biofilm formation. However, additional functions for c-di-GMP and roles for related molecules, such as c-di-AMP and c-AMP-GMP continue to be uncovered. The first usage of cyclic-di-nucleotide (c-di-NMP) signaling in the eukaryote domain emerged only recently. In dictyostelid social amoebas, c-di-GMP is a secreted signal that induces motile amoebas to differentiate into sessile stalk cells. In humans, c-di-NMPs, which are either produced endogenously in response to foreign DNA or by invading bacterial pathogens, trigger the innate immune system by activating the expression of interferon genes. STING, the human c-di-NMP receptor, is conserved throughout metazoa and their closest unicellular relatives, suggesting protist origins for human c-di-NMP signaling. Compared to the limited number of conserved protein domains that detect the second messengers cAMP and cGMP, the domains that detect the c-di-NMPs are surprisingly varied.

Topics: Bacterial Proteins; Biofilms; Cyclic GMP; Dictyostelium; Dinucleoside Phosphates; Humans; Immunity, Innate; Membrane Proteins; Nucleotides, Cyclic; Nucleotidyltransferases; Phylogeny; Protein Structure, Tertiary; Second Messenger Systems; Signal Transduction

Cyclic dinucleotides (CDNs) are key secondary messenger molecules produced by cyclic dinucleotide synthases that trigger various cellular signaling cascades from bacteria to vertebrates. In mammals, cyclic GMP-AMP synthase (cGAS) has been shown to bind to intracellular DNA and catalyze the production of the dinucleotide 2'3' cGAMP, which signals downstream effectors to regulate immune function, interferon signaling, and the antiviral response. Despite the importance of CDNs, sensitive and accurate methods to measure their levels in vivo are lacking. Here, we report a novel LC-MS/MS method to quantify CDNs in vivo. We characterized the mass spectrometric behavior of four different biologically relevant CDNs (c-di-AMP, c-di-GMP, 3'3' cGAMP, 2'3' cGAMP) and provided a means of visually representing fragmentation resulting from collision-induced dissociation at different energies using collision energy breakdown graphs. We then validated the method and quantified CDNs in two in vivo systems, the bacteria Escherichia coli OP50 and the killifish Nothobranchius furzeri. We found that optimization of LC-MS/MS parameters is crucial to sensitivity and accuracy. These technical advances should help illuminate physiological and pathological roles of these CDNs in in vivo settings. Graphical abstract.

Topics: Animals; Chromatography, Liquid; Cyclic GMP; Dinucleoside Phosphates; Escherichia coli; Fundulidae; Nucleotides, Cyclic; Tandem Mass Spectrometry

Many pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS) and lipoteichoic acid, are potent immunostimulatory molecules and promote the expression of cyclooxygenase 2 (COX-2). While the production of COX-2, and ultimately prostaglandin E

Topics: Animals; Beclin-1; Cell Line; Cyclic GMP; Cyclooxygenase 2; Dinucleoside Phosphates; Gene Expression Regulation; Guanine; Immunity, Innate; Interferon Regulatory Factor-3; Interferon Type I; Macrophages; Mice; NF-kappa B; Oligonucleotides; Phosphorylation; Prostaglandins; Signal Transduction

The Asp-His-His and Asp-His-His-associated (DHH/DHHA1) domain-containing phosphodiesterases (PDEs) that catalyze degradation of cyclic di-adenosine monophosphate (c-di-AMP) could be subdivided into two subfamilies based on the final product [5'-phosphadenylyl-adenosine (5'-pApA) or AMP]. In a previous study, we revealed that Rv2837c, a stand-alone DHH/DHHA1 PDE, employs a 5'-pApA internal flipping mechanism to produce AMPs. However, why the membrane-bound DHH/DHHA1 PDE can only degrade c-di-AMP to 5'-pApA remains obscure. Here, we report the crystal structure of the DHH/DHHA1 domain of GdpP (GdpP-C), and structures in complex with c-di-AMP, cyclic di-guanosine monophosphate (c-di-GMP), and 5'-pApA. Structural analysis reveals that GdpP-C binds nucleotide substrates quite differently from how Rv2837c does in terms of substrate-binding position. Accordingly, the nucleotide-binding site of the DHH/DHHA1 PDEs is organized into three (C, G, and R) subsites. For GdpP-C, in the C and G sites c-di-AMP binds and degrades into 5'-pApA, and its G site determines nucleotide specificity. To further degrade into AMPs, 5'-pApA must slide into the C and R sites for flipping and hydrolysis as in Rv2837c. Subsequent mutagenesis and enzymatic studies of GdpP-C and Rv2837c uncover the complete flipping process and reveal a unified catalytic mechanism for members of both DHH/DHHA1 PDE subfamilies.

Topics: Amino Acid Motifs; Bacterial Proteins; Binding Sites; Cloning, Molecular; Crystallography, X-Ray; Cyclic GMP; Dinucleoside Phosphates; Escherichia coli; Gene Expression; Genetic Vectors; Kinetics; Manganese; Models, Molecular; Mycobacterium tuberculosis; Phosphoric Diester Hydrolases; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Recombinant Proteins; Staphylococcus aureus; Substrate Specificity

Cyclic dinucleotides are second messenger molecules produced by both prokaryotes and eukaryotes in response to external stimuli. In bacteria, these molecules bind to RNA riboswitches and several protein receptors ultimately leading to phenotypic changes such as biofilm formation, ion transport and secretion of virulence factors. Some cyclic dinucleotide analogs bind differentially to biological receptors and can therefore be used to better understand cyclic dinucleotide mechanisms in vitro and in vivo. However, production of some of these analogs involves lengthy, multistep syntheses. Here, we describe a new, simple method for enzymatic synthesis of several 3', 5' linked cyclic dinucleotide analogs of c-di-GMP, c-di-AMP and c-AMP-GMP using the cyclic-AMP-GMP synthetase, DncV. The enzymatic reaction efficiently produced most cyclic dinucleotide analogs, such as 2'-amino sugar substitutions and phosphorothioate backbone modifications, for all three types of cyclic dinucleotides without the use of protecting groups or organic solvents. We used these novel analogs to explore differences in phosphate backbone and 2'-hydroxyl recognition between GEMM-I and GEMM-Ib riboswitches.

Topics: Algorithms; Bacterial Proteins; Cyclic GMP; Dinucleoside Phosphates; Kinetics; Ligases; Magnesium; Molecular Structure; Nucleotides, Cyclic; Protein Binding; Vibrio cholerae

Microneedle-based skin allergen-specific immunotherapy (AIT) can benefit from adjuvants that can stimulate a stronger Th1 response against the allergen. We evaluated two stimulator of interferon genes (STING) agonists, namely, cyclic diguanylate monophosphate (c-di-GMP) and cyclic diadenylate monophosphate (c-di-AMP), as skin adjuvants using coated microneedles (MNs). For comparison, the approved subcutaneous (SC) hypodermic injection containing alum was used. Ovalbumin (Ova) was used as a model allergen. Ova-specific IgG2a antibody in serum, which is a surrogate marker for Th1 type immune response was significantly higher when STING agonists were used with coated MNs as compared to SC injection of Ova+alum in mice. In contrast, IgG1 antibody, a surrogate marker for Th2 type immune response, was at comparable levels in the MN and SC groups. Restimulation of splenocytes with Ova produced higher levels of Th1 cytokines (IFN-γ and IL-2) in the STING agonists MN groups as compared to the SC group. In conclusion, delivery of STING agonists into the skin using coated MNs activated the Th1 pathway better than SC- and MN-based delivery of alum. Thus, STING agonists could fulfill the role of adjuvants for skin AIT and even for infectious disease vaccines, where stimulation of the Th1 pathway is of interest.

Topics: Adjuvants, Immunologic; Administration, Cutaneous; Allergens; Alum Compounds; Animals; Cyclic GMP; Desensitization, Immunologic; Dinucleoside Phosphates; Female; Membrane Proteins; Mice; Mice, Inbred BALB C; Models, Animal; Needles; Ovalbumin; Th1 Cells; Th2 Cells

Oral cavity acts as a reservoir of bacterial pathogens for systemic infections and several oral microorganisms have been linked to systemic diseases. Quorum sensing and cyclic dinucleotides, two "decision-making" signaling systems, communicate to regulate physiological process in bacteria. Discovery of cyclic dinucleotides has a long history, but the progress in our understanding of how cyclic dinucleotides regulate bacterial lifestyle is relatively new. Oral microorganisms form some of the most intricate biofilms, yet c-di-GMP, and c-di-AMP signaling have been rarely studied in oral biofilms. Recent studies demonstrated that, with the aid of bacterial messenger molecules and their analogs, it is possible to activate host innate and adaptive immune responses and epithelial integrity with a dose that is relevant to inhibit bacterial virulence mechanisms, such as fimbriae and exopolysaccharide production, biofilm formation, and host cell invasion. The aim of this perspective article is to present available information on cyclic dinucleotides in oral bacteria and in oral biofilms. Moreover, technologies that can be used to detect cyclic dinucleotides in oral biofilms are described. Finally, directions for future research are highlighted.

Topics: Adaptive Immunity; Bacteria; Bacterial Physiological Phenomena; Biofilms; Cyclic GMP; Dinucleoside Phosphates; Immunity, Innate; Mouth; Porphyromonas gingivalis; Quorum Sensing; Signal Transduction; Streptococcus mutans; Treponema denticola; Virulence

The cyclic dinucleotides (CDNs) c-di-GMP, c-di-AMP, and c-AMP-GMP are widely utilized as second messengers in bacteria, where they signal lifestyle changes such as motility and biofilm formation, cell wall and membrane homeostasis, virulence, and exo-electrogenesis. For all known bacterial CDNs, specific riboswitches have been identified that alter gene expression in response to the second messengers. In addition, bacterial CDNs trigger potent immune responses, making them attractive as adjuvants in immune therapies. Besides the three naturally occurring CDNs, seven further CDNs containing canonical 3'-5'-linkages are possible by combining the four natural ribonucleotides. Herein, we have synthesized all ten possible combinations of 3'-5'-linked CDNs. The binding affinity of novel CDNs and GEMM riboswitch variants was assessed utilizing a spinach aptamer fluorescence assay and in-line probing assays. The immune-stimulatory effect of CDNs was evaluated by induction of type I interferons (IFNs), and a novel CDN c-AMP-CMP was identified as a new immune-stimulatory agent.

Topics: Cyclic GMP; Dinucleoside Phosphates; Geobacter; Molecular Conformation

The intracellular infections of Mycobacterium tuberculosis, which is the causative agent of tuberculosis, are regulated by many cyclic dinucleotide signaling. Rv2837c from M. tuberculosis is a soluble, stand-alone DHH-DHHA1 domain phosphodiesterase that down-regulates c-di-AMP through catalytic degradation and plays an important role in M. tuberculosis infections. Here, we report the crystal structure of Rv2837c (2.0 Å), and its complex with hydrolysis intermediate 5'-pApA (2.35 Å). Our structures indicate that both DHH and DHHA1 domains are essential for c-di-AMP degradation. Further structural analysis shows that Rv2837c does not distinguish adenine from guanine, which explains why Rv2837c hydrolyzes all linear dinucleotides with almost the same efficiency. We observed that Rv2837c degraded other c-di-NMPs at a lower rate than it did on c-di-AMP. Nevertheless, our data also showed that Rv2837c significantly decreases concentrations of both c-di-AMP and c-di-GMP in vivo. Our results suggest that beside its major role in c-di-AMP degradation Rv2837c could also regulate c-di-GMP signaling pathways in bacterial cell.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; 3',5'-Cyclic-GMP Phosphodiesterases; Amino Acid Sequence; Bacterial Proteins; Biocatalysis; Catalytic Domain; Conserved Sequence; Cyclic AMP; Cyclic GMP; Dinucleoside Phosphates; Exoribonucleases; Models, Molecular; Molecular Sequence Data; Mutation; Mycobacterium tuberculosis; Peptide Fragments; Protein Conformation; Recombinant Fusion Proteins; Recombinant Proteins; Sequence Alignment; Substrate Specificity

cAMP mediates autonomic regulation of heart rate by means of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which underlie the pacemaker current If. cAMP binding to the C-terminal cyclic nucleotide binding domain enhances HCN open probability through a conformational change that reaches the pore via the C-linker. Using structural and functional analysis, we identified a binding pocket in the C-linker of HCN4. Cyclic dinucleotides, an emerging class of second messengers in mammals, bind the C-linker pocket (CLP) and antagonize cAMP regulation of the channel. Accordingly, cyclic dinucleotides prevent cAMP regulation of If in sinoatrial node myocytes, reducing heart rate by 30%. Occupancy of the CLP hence constitutes an efficient mechanism to hinder β-adrenergic stimulation on If. Our results highlight the regulative role of the C-linker and identify a potential drug target in HCN4. Furthermore, these data extend the signaling scope of cyclic dinucleotides in mammals beyond their first reported role in innate immune system.

Topics: Animals; Binding Sites; Blotting, Western; Crystallography, X-Ray; Cyclic AMP; Cyclic GMP; Dinucleoside Phosphates; HEK293 Cells; High-Throughput Screening Assays; Humans; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Ion Channel Gating; Ligands; Mice; Mice, Inbred C57BL; Molecular Docking Simulation; Molecular Structure; Muscle Proteins; Myocytes, Cardiac; Patch-Clamp Techniques; Potassium Channels; Sinoatrial Node; Small Molecule Libraries; Transfection

Deciphering the molecular basis of HCN channel regulation by cGMP leads to the serendipitous discovery of cyclic dinucleotides as potent inhibitors of I(f) current in the heart.

Topics: Animals; Cyclic AMP; Cyclic GMP; Dinucleoside Phosphates; Humans; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Ion Channel Gating; Muscle Proteins; Potassium Channels

The cyclic dinucleotides 3'-5'diadenylate (c-diAMP) and 3'-5' diguanylate (c-diGMP) are important bacterial second messengers that have recently been shown to stimulate the secretion of type I Interferons (IFN-Is) through the c-diGMP-binding protein MPYS/STING. Here, we show that physiologically relevant levels of cyclic dinucleotides also stimulate a robust secretion of IL-1β through the NLRP3 inflammasome. Intriguingly, this response is independent of MPYS/STING. Consistent with most NLRP3 inflammasome activators, the response to c-diGMP is dependent on the mobilization of potassium and calcium ions. However, in contrast to other NLRP3 inflammasome activators, this response is not associated with significant changes in mitochondrial potential or the generation of mitochondrial reactive oxygen species. Thus, cyclic dinucleotides activate the NLRP3 inflammasome through a unique pathway that could have evolved to detect pervasive bacterial pathogen-associated molecular patterns associated with intracellular infections.

Topics: Animals; Calcium; Carrier Proteins; Cell Line, Tumor; Cyclic GMP; Dinucleoside Phosphates; Humans; Inflammasomes; Interleukin-1beta; Macrophages; Membrane Potential, Mitochondrial; Membrane Proteins; Mice; Mice, Inbred C57BL; NLR Family, Pyrin Domain-Containing 3 Protein; Potassium; Reactive Oxygen Species

The biotinylated c-di-GMP and c-di-AMP conjugates 10a/b were synthesized by a straightforward set of procedures from standard, commercially available phosphoramidites. Their availability should allow isolation and characterization of new protein and RNA receptors for these key bacterial signaling molecules.

Topics: Biotinylation; Chemical Precipitation; Click Chemistry; Crystallization; Cyclic GMP; Dinucleoside Phosphates; Organophosphorus Compounds

Macrophages respond to infection with Legionella pneumophila by the induction of inflammatory mediators, including type I Interferons (IFN-Is). To explore whether the bacterial second messenger cyclic 3'-5' diguanylate (c-diGMP) activates some of these mediators, macrophages were infected with L. pneumophila strains in which the levels of bacterial c-diGMP had been altered. Intriguingly, there was a positive correlation between c-diGMP levels and IFN-I expression. Subsequent studies with synthetic derivatives of c-diGMP, and newly described cyclic 3'-5' diadenylate (c-diAMP), determined that these molecules activate overlapping inflammatory responses in human and murine macrophages. Moreover, UV crosslinking studies determined that both dinucleotides physically associate with a shared set of host proteins. Fractionation of macrophage extracts on a biotin-c-diGMP affinity matrix led to the identification of a set of candidate host binding proteins. These studies suggest that mammalian macrophages can sense and mount a specific inflammatory response to bacterial dinucleotides.

Topics: Animals; Bacterial Proteins; Cell Line; Cyclic GMP; Dinucleoside Phosphates; Gene Expression Regulation, Bacterial; Host-Pathogen Interactions; Humans; Interferon Type I; Interferon-beta; Legionella pneumophila; Macrophages; Mice; Mice, Inbred C57BL; Mice, Knockout; Signal Transduction

The induction of type I interferons by the bacterial secondary messengers cyclic di-GMP (c-di-GMP) or cyclic di-AMP (c-di-AMP) is dependent on a signaling axis that involves the adaptor STING, the kinase TBK1 and the transcription factor IRF3. Here we identified the heliase DDX41 as a pattern-recognition receptor (PRR) that sensed both c-di-GMP and c-di-AMP. DDX41 specifically and directly interacted with c-di-GMP. Knockdown of DDX41 via short hairpin RNA in mouse or human cells inhibited the induction of genes encoding molecules involved in the innate immune response and resulted in defective activation of STING, TBK1 and IRF3 in response to c-di-GMP or c-di-AMP. Our results suggest a mechanism whereby c-di-GMP and c-di-AMP are detected by DDX41, which forms a complex with STING to signal to TBK1-IRF3 and activate the interferon response.

Topics: Animals; Cell Line; Cyclic GMP; DEAD-box RNA Helicases; Dinucleoside Phosphates; Humans; Immunity, Innate; Interferon Regulatory Factor-3; Interferon Type I; Listeria monocytogenes; Macrophages; Membrane Proteins; Mice; Protein Serine-Threonine Kinases; Receptors, Pattern Recognition; RNA Interference; RNA, Small Interfering; Second Messenger Systems; Signal Transduction

Topics: Animals; Cyclic GMP; DEAD-box RNA Helicases; Dinucleoside Phosphates; Humans; Interferon Type I; Listeria monocytogenes; Receptors, Pattern Recognition

Type I interferons (IFNs) are central regulators of the innate and adaptive immune responses to viral and bacterial infections. Type I IFNs are induced upon cytosolic detection of microbial nucleic acids, including DNA, RNA, and the bacterial second messenger cyclic-di-GMP (c-di-GMP). In addition, a recent study demonstrated that the intracellular bacterial pathogen Listeria monocytogenes stimulates a type I IFN response due to cytosolic detection of bacterially secreted c-di-AMP. The transmembrane signaling adaptor Sting (Tmem173, Mita, Mpys, Eris) has recently been implicated in the induction of type I IFNs in response to cytosolic DNA and/or RNA. However, the role of Sting in response to purified cyclic dinucleotides or during in vivo L. monocytogenes infection has not been addressed. In order to identify genes important in the innate immune response, we have been conducting a forward genetic mutagenesis screen in C57BL/6 mice using the mutagen N-ethyl-N-nitrosourea (ENU). Here we describe a novel mutant mouse strain, Goldenticket (Gt), that fails to produce type I IFNs upon L. monocytogenes infection. By genetic mapping and complementation experiments, we found that Gt mice harbor a single nucleotide variant (T596A) of Sting that functions as a null allele and fails to produce detectable protein. Analysis of macrophages isolated from Gt mice revealed that Sting is absolutely required for the type I interferon response to both c-di-GMP and c-di-AMP. Additionally, Sting is required for the response to c-di-GMP and L. monocytogenes in vivo. Our results provide new functions for Sting in the innate interferon response to pathogens.

Topics: Alleles; Animals; Cell Line; Cyclic GMP; Dinucleoside Phosphates; Ethylnitrosourea; Female; Gene Expression Regulation; Genetic Complementation Test; Humans; Interferon Type I; Listeria monocytogenes; Listeriosis; Macrophages; Male; Membrane Proteins; Mice; Mice, Mutant Strains; Mutation; Polymorphism, Single Nucleotide

The second messenger signaling molecule bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) regulates many processes in bacteria, including motility, pathogenesis and biofilm formation. c-di-GMP-binding riboswitches are important downstream targets in this signaling pathway. Here we report the crystal structure, at 2.7 A resolution, of a c-di-GMP riboswitch aptamer from Vibrio cholerae bound to c-di-GMP, showing that the ligand binds within a three-helix junction that involves base-pairing and extensive base-stacking. The symmetric c-di-GMP is recognized asymmetrically with respect to both the bases and the backbone. A mutant aptamer was engineered that preferentially binds the candidate signaling molecule c-di-AMP over c-di-GMP. Kinetic and structural data suggest that genetic regulation by the c-di-GMP riboswitch is kinetically controlled and that gene expression is modulated through the stabilization of a previously unidentified P1 helix, illustrating a direct mechanism for c-di-GMP signaling.

Topics: Base Pairing; Crystallography, X-Ray; Cyclic GMP; Dinucleoside Phosphates; Gene Expression Regulation, Bacterial; Intercalating Agents; Kinetics; Models, Molecular; Nucleic Acid Conformation; RNA, Bacterial; Scattering, Small Angle; Second Messenger Systems; Vibrio cholerae