RESUMO
Animal and bacterial cells sense and defend against viral infections using evolutionarily conserved antiviral signaling pathways. Here, we show that viruses overcome host signaling using mechanisms of immune evasion that are directly shared across the eukaryotic and prokaryotic kingdoms of life. Structures of animal poxvirus proteins that inhibit host cGAS-STING signaling demonstrate architectural and catalytic active-site homology shared with bacteriophage Acb1 proteins, which inactivate CBASS anti-phage defense. In bacteria, phage Acb1 proteins are viral enzymes that degrade host cyclic nucleotide immune signals. Structural comparisons of poxvirus protein-2'3'-cGAMP and phage Acb1-3'3'-cGAMP complexes reveal a universal mechanism of host nucleotide immune signal degradation and explain kingdom-specific additions that enable viral adaptation. Chimeric bacteriophages confirm that animal poxvirus proteins are sufficient to evade immune signaling in bacteria. Our findings identify a mechanism of immune evasion conserved between animal and bacterial viruses and define shared rules that explain host-virus interactions across multiple kingdoms of life.
RESUMO
RADAR is a two-protein bacterial defense system that was reported to defend against phage by "editing" messenger RNA. Here, we determine cryo-EM structures of the RADAR defense complex, revealing RdrA as a heptameric, two-layered AAA+ ATPase and RdrB as a dodecameric, hollow complex with twelve surface-exposed deaminase active sites. RdrA and RdrB join to form a giant assembly up to 10 MDa, with RdrA docked as a funnel over the RdrB active site. Surprisingly, our structures reveal an RdrB active site that targets mononucleotides. We show that RdrB catalyzes ATP-to-ITP conversion in vitro and induces the massive accumulation of inosine mononucleotides during phage infection in vivo, limiting phage replication. Our results define ATP mononucleotide deamination as a determinant of RADAR immunity and reveal supramolecular assembly of a nucleotide-modifying machine as a mechanism of anti-phage defense.
Assuntos
Bacteriófagos , Bacteriófagos/metabolismo , Microscopia Crioeletrônica/métodos , ATPases Associadas a Diversas Atividades Celulares , Trifosfato de Adenosina , Adenosina Desaminase/metabolismoRESUMO
Cyclic GMP-AMP synthase (cGAS) is an enzyme in human cells that controls an immune response to cytosolic DNA. Upon binding DNA, cGAS synthesizes a nucleotide signal 2'3'-cGAMP that activates STING-dependent downstream immunity. Here, we discover that cGAS-like receptors (cGLRs) constitute a major family of pattern recognition receptors in innate immunity. Building on recent analysis in Drosophila, we identify >3,000 cGLRs present in nearly all metazoan phyla. A forward biochemical screening of 150 animal cGLRs reveals a conserved mechanism of signaling including response to dsDNA and dsRNA ligands and synthesis of isomers of the nucleotide signals cGAMP, c-UMP-AMP, and c-di-AMP. Combining structural biology and in vivo analysis in coral and oyster animals, we explain how synthesis of distinct nucleotide signals enables cells to control discrete cGLR-STING signaling pathways. Our results reveal cGLRs as a widespread family of pattern recognition receptors and establish molecular rules that govern nucleotide signaling in animal immunity.
Assuntos
Imunidade Inata , Nucleotidiltransferases , Humanos , Animais , Nucleotidiltransferases/metabolismo , Imunidade Inata/genética , Transdução de Sinais/genética , DNA/metabolismo , Receptores de Reconhecimento de PadrãoRESUMO
Low-molecular-weight (LMW) thiols are small-molecule antioxidants required for the maintenance of intracellular redox homeostasis. However, many host-associated microbes, including the gastric pathogen Helicobacter pylori, unexpectedly lack LMW-thiol biosynthetic pathways. Using reactivity-guided metabolomics, we identified the unusual LMW thiol ergothioneine (EGT) in H. pylori. Dietary EGT accumulates to millimolar levels in human tissues and has been broadly implicated in mitigating disease risk. Although certain microorganisms synthesize EGT, we discovered that H. pylori acquires this LMW thiol from the host environment using a highly selective ATP-binding cassette transporter-EgtUV. EgtUV confers a competitive colonization advantage in vivo and is widely conserved in gastrointestinal microbes. Furthermore, we found that human fecal bacteria metabolize EGT, which may contribute to production of the disease-associated metabolite trimethylamine N-oxide. Collectively, our findings illustrate a previously unappreciated mechanism of microbial redox regulation in the gut and suggest that inter-kingdom competition for dietary EGT may broadly impact human health.
Assuntos
Ergotioneína , Humanos , Ergotioneína/metabolismo , Antioxidantes/metabolismo , Oxirredução , Compostos de Sulfidrila , Peso MolecularRESUMO
The cyclic pyrimidines 3',5'-cyclic cytidine monophosphate (cCMP) and 3',5'-cyclic uridine monophosphate (cUMP) have been reported in multiple organisms and cell types. As opposed to the cyclic nucleotides 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP), which are second messenger molecules with well-established regulatory roles across all domains of life, the biological role of cyclic pyrimidines has remained unclear. Here we report that cCMP and cUMP are second messengers functioning in bacterial immunity against viruses. We discovered a family of bacterial pyrimidine cyclase enzymes that specifically synthesize cCMP and cUMP following phage infection and demonstrate that these molecules activate immune effectors that execute an antiviral response. A crystal structure of a uridylate cyclase enzyme from this family explains the molecular mechanism of selectivity for pyrimidines as cyclization substrates. Defense systems encoding pyrimidine cyclases, denoted here Pycsar (pyrimidine cyclase system for antiphage resistance), are widespread in prokaryotes. Our results assign clear biological function to cCMP and cUMP as immunity signaling molecules in bacteria.
Assuntos
Bactérias/imunologia , Bactérias/virologia , Bacteriófagos/fisiologia , CMP Cíclico/metabolismo , Nucleotídeos Cíclicos/metabolismo , Uridina Monofosfato/metabolismo , Sequência de Aminoácidos , Bactérias/genética , Burkholderia/enzimologia , CMP Cíclico/química , Ciclização , Escherichia coli/enzimologia , Modelos Moleculares , Mutação/genética , Nucleotídeos Cíclicos/química , Fósforo-Oxigênio Liases/química , Fósforo-Oxigênio Liases/metabolismo , Pirimidinas/metabolismo , Uridina Monofosfato/químicaRESUMO
cGAS/DncV-like nucleotidyltransferase (CD-NTase) enzymes are immune sensors that synthesize nucleotide second messengers and initiate antiviral responses in bacterial and animal cells. Here, we discover Enterobacter cloacae CD-NTase-associated protein 4 (Cap4) as a founding member of a diverse family of >2,000 bacterial receptors that respond to CD-NTase signals. Structures of Cap4 reveal a promiscuous DNA endonuclease domain activated through ligand-induced oligomerization. Oligonucleotide recognition occurs through an appended SAVED domain that is an unexpected fusion of two CRISPR-associated Rossman fold (CARF) subunits co-opted from type III CRISPR immunity. Like a lock and key, SAVED effectors exquisitely discriminate 2'-5'- and 3'-5'-linked bacterial cyclic oligonucleotide signals and enable specific recognition of at least 180 potential nucleotide second messenger species. Our results reveal SAVED CARF family proteins as major nucleotide second messenger receptors in CBASS and CRISPR immune defense and extend the importance of linkage specificity beyond mammalian cGAS-STING signaling.
Assuntos
Bactérias/virologia , Bacteriófagos/metabolismo , Sistemas CRISPR-Cas , Imunidade , Oligonucleotídeos/metabolismo , Transdução de Sinais , Sequência de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Desoxirribonuclease I/metabolismo , Ligantes , Mutagênese/genética , Nucleotidiltransferases/metabolismo , Ligação Proteica , Sistemas do Segundo MensageiroRESUMO
The presence of DNA in the cytosol of mammalian cells is an unusual event that is often associated with genotoxic stress or viral infection. The enzyme cGAS is a sensor of cytosolic DNA that induces interferon and inflammatory responses that can be protective or pathologic, depending on the context. Along with other cytosolic innate immune receptors, cGAS is thought to diffuse throughout the cytosol in search of its DNA ligand. Herein, we report that cGAS is not a cytosolic protein but rather localizes to the plasma membrane via the actions of an N-terminal phosphoinositide-binding domain. This domain interacts selectively with PI(4,5)P2, and cGAS mutants defective for lipid binding are mislocalized to the cytosolic and nuclear compartments. Mislocalized cGAS induces potent interferon responses to genotoxic stress, but weaker responses to viral infection. These data establish the subcellular positioning of a cytosolic innate immune receptor as a mechanism that governs self-nonself discrimination.
Assuntos
Membrana Celular/fisiologia , Nucleotidiltransferases/metabolismo , Fosfatidilinositol 4,5-Difosfato/metabolismo , Animais , Linhagem Celular , Membrana Celular/metabolismo , Citosol/fisiologia , DNA Viral/genética , Feminino , Células HEK293 , Células HeLa , Interações Hospedeiro-Patógeno , Humanos , Imunidade Inata/fisiologia , Interferons/metabolismo , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Nucleotidiltransferases/fisiologia , Fosfatidilinositol 4,5-Difosfato/fisiologia , Fosfatidilinositóis , Ligação Proteica , Transdução de Sinais/imunologiaRESUMO
Cyclic GMP-AMP synthase (cGAS) recognition of cytosolic DNA is critical for immune responses to pathogen replication, cellular stress, and cancer. Existing structures of the mouse cGAS-DNA complex provide a model for enzyme activation but do not explain why human cGAS exhibits severely reduced levels of cyclic GMP-AMP (cGAMP) synthesis compared to other mammals. Here, we discover that enhanced DNA-length specificity restrains human cGAS activation. Using reconstitution of cGAMP signaling in bacteria, we mapped the determinant of human cGAS regulation to two amino acid substitutions in the DNA-binding surface. Human-specific substitutions are necessary and sufficient to direct preferential detection of long DNA. Crystal structures reveal why removal of human substitutions relaxes DNA-length specificity and explain how human-specific DNA interactions favor cGAS oligomerization. These results define how DNA-sensing in humans adapted for enhanced specificity and provide a model of the active human cGAS-DNA complex to enable structure-guided design of cGAS therapeutics.
Assuntos
DNA/metabolismo , Vigilância Imunológica/fisiologia , Nucleotidiltransferases/metabolismo , Animais , Benzofuranos/química , Benzofuranos/metabolismo , Sítios de Ligação , Domínio Catalítico , Quimiotaxia/efeitos dos fármacos , DNA/química , Humanos , Camundongos , Simulação de Acoplamento Molecular , Mutagênese Sítio-Dirigida , Nucleotídeos Cíclicos/metabolismo , Nucleotídeos Cíclicos/farmacologia , Nucleotidiltransferases/antagonistas & inibidores , Nucleotidiltransferases/genética , Multimerização Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Especificidade da Espécie , Vibrio cholerae/metabolismo , Vibrio cholerae/fisiologiaRESUMO
In mammals, the enzyme cGAS senses the presence of cytosolic DNA and synthesizes the cyclic dinucleotide (CDN) 2'3'-cGAMP, which triggers STING-dependent immunity. In Drosophila melanogaster, two cGAS-like receptors (cGLRs) produce 3'2'-cGAMP and 2'3'-cGAMP to activate STING. We explored CDN-mediated immunity in 14 Drosophila species covering 50 million years of evolution and found that 2'3'-cGAMP and 3'2'-cGAMP failed to control infection by Drosophila C virus in D. serrata and two other species. We discovered diverse CDNs produced in a cGLR-dependent manner in response to viral infection in D. melanogaster, including 2'3'-c-di-GMP. This CDN was a more potent STING agonist than cGAMP in D. melanogaster and it also activated a strong antiviral transcriptional response in D. serrata. Our results shed light on the evolution of cGLRs in flies and provide a basis for understanding the function and regulation of this emerging family of pattern recognition receptors in animal innate immunity.
Assuntos
Antivirais , Drosophila , Animais , Drosophila melanogaster , GMP Cíclico , MamíferosRESUMO
Chromatin modification and higher-order chromosome structure play key roles in gene regulation, but their functional interplay in controlling gene expression is elusive. We have discovered the machinery and mechanism underlying the dynamic enrichment of histone modification H4K20me1 on hermaphrodite X chromosomes during C. elegans dosage compensation and demonstrated H4K20me1's pivotal role in regulating higher-order chromosome structure and X-chromosome-wide gene expression. The structure and the activity of the dosage compensation complex (DCC) subunit DPY-21 define a Jumonji demethylase subfamily that converts H4K20me2 to H4K20me1 in worms and mammals. Selective inactivation of demethylase activity eliminates H4K20me1 enrichment in somatic cells, elevates X-linked gene expression, reduces X chromosome compaction, and disrupts X chromosome conformation by diminishing the formation of topologically associating domains (TADs). Unexpectedly, DPY-21 also associates with autosomes of germ cells in a DCC-independent manner to enrich H4K20me1 and trigger chromosome compaction. Our findings demonstrate the direct link between chromatin modification and higher-order chromosome structure in long-range regulation of gene expression.
Assuntos
Proteínas de Caenorhabditis elegans/química , Proteínas de Caenorhabditis elegans/metabolismo , Proteínas de Transporte/química , Proteínas de Transporte/metabolismo , Regulação da Expressão Gênica , Cromossomo X/química , Sequência de Aminoácidos , Animais , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Transporte/genética , Mecanismo Genético de Compensação de Dose , Embrião não Mamífero/metabolismo , Histona Desmetilases com o Domínio Jumonji/química , Histona Desmetilases com o Domínio Jumonji/metabolismo , Modelos Moleculares , Mutação , Piperidinas/metabolismo , Alinhamento de Sequência , Tiofenos/metabolismoRESUMO
CRISPR-Cas9 proteins function within bacterial immune systems to target and destroy invasive DNA and have been harnessed as a robust technology for genome editing. Small bacteriophage-encoded anti-CRISPR proteins (Acrs) can inactivate Cas9, providing an efficient off switch for Cas9-based applications. Here, we show that two Acrs, AcrIIC1 and AcrIIC3, inhibit Cas9 by distinct strategies. AcrIIC1 is a broad-spectrum Cas9 inhibitor that prevents DNA cutting by multiple divergent Cas9 orthologs through direct binding to the conserved HNH catalytic domain of Cas9. A crystal structure of an AcrIIC1-Cas9 HNH domain complex shows how AcrIIC1 traps Cas9 in a DNA-bound but catalytically inactive state. By contrast, AcrIIC3 blocks activity of a single Cas9 ortholog and induces Cas9 dimerization while preventing binding to the target DNA. These two orthogonal mechanisms allow for separate control of Cas9 target binding and cleavage and suggest applications to allow DNA binding while preventing DNA cutting by Cas9.
Assuntos
Sistemas CRISPR-Cas , Endonucleases/antagonistas & inibidores , Proteínas Virais/metabolismo , Sequência de Aminoácidos , Proteínas de Bactérias/antagonistas & inibidores , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bacteriófagos/genética , Bacteriófagos/metabolismo , Endonucleases/química , Endonucleases/genética , Endonucleases/metabolismo , Evolução Molecular , Células HEK293 , Humanos , Domínios Proteicos , Alinhamento de SequênciaRESUMO
In response to pathogen infection, gasdermin (GSDM) proteins form membrane pores that induce a host cell death process called pyroptosis1-3. Studies of human and mouse GSDM pores have revealed the functions and architectures of assemblies comprising 24 to 33 protomers4-9, but the mechanism and evolutionary origin of membrane targeting and GSDM pore formation remain unknown. Here we determine a structure of a bacterial GSDM (bGSDM) pore and define a conserved mechanism of pore assembly. Engineering a panel of bGSDMs for site-specific proteolytic activation, we demonstrate that diverse bGSDMs form distinct pore sizes that range from smaller mammalian-like assemblies to exceptionally large pores containing more than 50 protomers. We determine a cryo-electron microscopy structure of a Vitiosangium bGSDM in an active 'slinky'-like oligomeric conformation and analyse bGSDM pores in a native lipid environment to create an atomic-level model of a full 52-mer bGSDM pore. Combining our structural analysis with molecular dynamics simulations and cellular assays, our results support a stepwise model of GSDM pore assembly and suggest that a covalently bound palmitoyl can leave a hydrophobic sheath and insert into the membrane before formation of the membrane-spanning ß-strand regions. These results reveal the diversity of GSDM pores found in nature and explain the function of an ancient post-translational modification in enabling programmed host cell death.
Assuntos
Gasderminas , Myxococcales , Microscopia Crioeletrônica , Gasderminas/química , Gasderminas/metabolismo , Gasderminas/ultraestrutura , Interações Hidrofóbicas e Hidrofílicas , Lipídeos de Membrana/química , Lipídeos de Membrana/metabolismo , Simulação de Dinâmica Molecular , Myxococcales/química , Myxococcales/citologia , Myxococcales/ultraestrutura , Estrutura Quaternária de Proteína , Subunidades Proteicas/química , Subunidades Proteicas/metabolismo , Proteólise , PiroptoseRESUMO
Bacteria encode hundreds of diverse defence systems that protect them from viral infection and inhibit phage propagation1-5. Gabija is one of the most prevalent anti-phage defence systems, occurring in more than 15% of all sequenced bacterial and archaeal genomes1,6,7, but the molecular basis of how Gabija defends cells from viral infection remains poorly understood. Here we use X-ray crystallography and cryo-electron microscopy (cryo-EM) to define how Gabija proteins assemble into a supramolecular complex of around 500 kDa that degrades phage DNA. Gabija protein A (GajA) is a DNA endonuclease that tetramerizes to form the core of the anti-phage defence complex. Two sets of Gabija protein B (GajB) dimers dock at opposite sides of the complex and create a 4:4 GajA-GajB assembly (hereafter, GajAB) that is essential for phage resistance in vivo. We show that a phage-encoded protein, Gabija anti-defence 1 (Gad1), directly binds to the Gabija GajAB complex and inactivates defence. A cryo-EM structure of the virally inhibited state shows that Gad1 forms an octameric web that encases the GajAB complex and inhibits DNA recognition and cleavage. Our results reveal the structural basis of assembly of the Gabija anti-phage defence complex and define a unique mechanism of viral immune evasion.
Assuntos
Bactérias , Proteínas de Bactérias , Bacteriófagos , Evasão da Resposta Imune , Multimerização Proteica , Bactérias/genética , Bactérias/imunologia , Bactérias/metabolismo , Bactérias/virologia , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Proteínas de Bactérias/ultraestrutura , Bacteriófagos/genética , Bacteriófagos/imunologia , Bacteriófagos/metabolismo , Microscopia Crioeletrônica , Cristalografia por Raios X , Desoxirribonucleases/química , Desoxirribonucleases/metabolismo , Desoxirribonucleases/ultraestrutura , DNA Viral/química , DNA Viral/metabolismo , DNA Viral/ultraestruturaRESUMO
It was recently shown that bacteria use, apart from CRISPR-Cas and restriction systems, a considerable diversity of phage resistance systems1-4, but it is largely unknown how phages cope with this multilayered bacterial immunity. Here we analysed groups of closely related Bacillus phages that showed differential sensitivity to bacterial defence systems, and discovered four distinct families of anti-defence proteins that inhibit the Gabija, Thoeris and Hachiman systems. We show that these proteins Gad1, Gad2, Tad2 and Had1 efficiently cancel the defensive activity when co-expressed with the respective defence system or introduced into phage genomes. Homologues of these anti-defence proteins are found in hundreds of phages that infect taxonomically diverse bacterial species. We show that the anti-Gabija protein Gad1 blocks the ability of the Gabija defence complex to cleave phage-derived DNA. Our data further reveal that the anti-Thoeris protein Tad2 is a 'sponge' that sequesters the immune signalling molecules produced by Thoeris TIR-domain proteins in response to phage infection. Our results demonstrate that phages encode an arsenal of anti-defence proteins that can disable a variety of bacterial defence mechanisms.
Assuntos
Fagos Bacilares , Bactérias , Proteínas Virais , Fagos Bacilares/classificação , Fagos Bacilares/genética , Fagos Bacilares/imunologia , Fagos Bacilares/metabolismo , Bactérias/classificação , Bactérias/genética , Bactérias/imunologia , Bactérias/virologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , DNA Viral/genética , DNA Viral/metabolismo , Proteínas Virais/genética , Proteínas Virais/metabolismoRESUMO
Bacteria encode an arsenal of diverse systems that defend against phage infection. A common theme uniting many prevalent antiphage defense systems is the use of specialized nucleotide signals that function as second messengers to activate downstream effector proteins and inhibit viral propagation. In this article, we review the molecular mechanisms controlling nucleotide immune signaling in four major families of antiphage defense systems: CBASS, Pycsar, Thoeris, and type III CRISPR immunity. Analyses of the individual steps connecting phage detection, nucleotide signal synthesis, and downstream effector function reveal shared core principles of signaling and uncover system-specific strategies used to augment immune defense. We compare recently discovered mechanisms used by phages to evade nucleotide immune signaling and highlight convergent strategies that shape host-virus interactions. Finally, we explain how the evolutionary connection between bacterial antiphage defense and eukaryotic antiviral immunity defines fundamental rules that govern nucleotide-based immunity across all kingdoms of life.
RESUMO
Cyclic dinucleotides (CDNs) play central roles in bacterial pathogenesis and innate immunity. The mammalian enzyme cGAS synthesizes a unique cyclic dinucleotide (cGAMP) containing a 2'-5' phosphodiester linkage essential for optimal immune stimulation, but the molecular basis for linkage specificity is unknown. Here, we show that the Vibrio cholerae pathogenicity factor DncV is a prokaryotic cGAS-like enzyme whose activity provides a mechanistic rationale for the unique ability of cGAS to produce 2'-5' cGAMP. Three high-resolution crystal structures show that DncV and human cGAS generate CDNs in sequential reactions that proceed in opposing directions. We explain 2' and 3' linkage specificity and test this model by reprogramming the human cGAS active site to produce 3'-5' cGAMP, leading to selective stimulation of alternative STING adaptor alleles in cells. These results demonstrate mechanistic homology between bacterial signaling and mammalian innate immunity and explain how active site configuration controls linkage chemistry for pathway-specific signaling.
Assuntos
Nucleotidiltransferases/química , Engenharia de Proteínas , Vibrio cholerae/enzimologia , Sequência de Aminoácidos , Domínio Catalítico , Humanos , Imunidade Inata , Modelos Moleculares , Dados de Sequência Molecular , Nucleotidiltransferases/metabolismo , Alinhamento de Sequência , Especificidade por SubstratoRESUMO
Cyclic GMP-AMP synthase (cGAS) recognition of cytosolic DNA is critical for the immune response to cancer and pathogen infection. Here, we discover that cGAS-DNA phase separation is required to resist negative regulation and allow efficient sensing of immunostimulatory DNA. We map the molecular determinants of cGAS condensate formation and demonstrate that phase separation functions to limit activity of the cytosolic exonuclease TREX1. Mechanistically, phase separation forms a selective environment that suppresses TREX1 catalytic function and restricts DNA degradation to an outer shell at the droplet periphery. We identify a TREX1 mutation associated with the severe autoimmune disease Aicardi-Goutières syndrome that increases penetration of TREX1 into the repressive droplet interior and specifically impairs degradation of phase-separated DNA. Our results define a critical function of cGAS-DNA phase separation and reveal a molecular mechanism that balances cytosolic DNA degradation and innate immune activation.
Assuntos
Doenças Autoimunes do Sistema Nervoso/enzimologia , Citosol/metabolismo , DNA/metabolismo , Exodesoxirribonucleases/metabolismo , Mutação , Malformações do Sistema Nervoso/enzimologia , Nucleotidiltransferases/metabolismo , Fosfoproteínas/metabolismo , Doenças Autoimunes do Sistema Nervoso/genética , Catálise , Linhagem Celular Tumoral , DNA/genética , Exodesoxirribonucleases/genética , Células HEK293 , Humanos , Malformações do Sistema Nervoso/genética , Nucleotidiltransferases/genética , Fosfoproteínas/genéticaRESUMO
Cyclic oligonucleotide-based antiphage signaling systems (CBASS) are antiviral defense operons that protect bacteria from phage replication. Here, we discover a widespread class of CBASS transmembrane (TM) effector proteins that respond to antiviral nucleotide signals and limit phage propagation through direct membrane disruption. Crystal structures of the Yersinia TM effector Cap15 reveal a compact 8-stranded ß-barrel scaffold that forms a cyclic dinucleotide receptor domain that oligomerizes upon activation. We demonstrate that activated Cap15 relocalizes throughout the cell and specifically induces rupture of the inner membrane. Screening for active effectors, we identify the function of distinct families of CBASS TM effectors and demonstrate that cell death via disruption of inner-membrane integrity is a common mechanism of defense. Our results reveal the function of the most prominent class of effector protein in CBASS immunity and define disruption of the inner membrane as a widespread strategy of abortive infection in bacterial phage defense.
Assuntos
Proteínas de Bactérias/metabolismo , Bacteriófagos/patogenicidade , Membrana Celular/virologia , Escherichia coli/virologia , Yersinia/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Bacteriófagos/imunologia , Morte Celular , Membrana Celular/genética , Membrana Celular/metabolismo , Escherichia coli/genética , Escherichia coli/imunologia , Escherichia coli/metabolismo , Interações Hospedeiro-Patógeno , Ligantes , Conformação Proteica , Multimerização Proteica , Transporte Proteico , Transdução de Sinais , Relação Estrutura-Atividade , Yersinia/genéticaRESUMO
The cyclic oligonucleotide-based antiphage signalling system (CBASS) and the pyrimidine cyclase system for antiphage resistance (Pycsar) are antiphage defence systems in diverse bacteria that use cyclic nucleotide signals to induce cell death and prevent viral propagation1,2. Phages use several strategies to defeat host CRISPR and restriction-modification systems3-10, but no mechanisms are known to evade CBASS and Pycsar immunity. Here we show that phages encode anti-CBASS (Acb) and anti-Pycsar (Apyc) proteins that counteract defence by specifically degrading cyclic nucleotide signals that activate host immunity. Using a biochemical screen of 57 phages in Escherichia coli and Bacillus subtilis, we discover Acb1 from phage T4 and Apyc1 from phage SBSphiJ as founding members of distinct families of immune evasion proteins. Crystal structures of Acb1 in complex with 3'3'-cyclic GMP-AMP define a mechanism of metal-independent hydrolysis 3' of adenosine bases, enabling broad recognition and degradation of cyclic dinucleotide and trinucleotide CBASS signals. Structures of Apyc1 reveal a metal-dependent cyclic NMP phosphodiesterase that uses relaxed specificity to target Pycsar cyclic pyrimidine mononucleotide signals. We show that Acb1 and Apyc1 block downstream effector activation and protect from CBASS and Pycsar defence in vivo. Active Acb1 and Apyc1 enzymes are conserved in phylogenetically diverse phages, demonstrating that cleavage of host cyclic nucleotide signals is a key strategy of immune evasion in phage biology.
Assuntos
Bacteriófagos , Bactérias/metabolismo , Proteínas de Bactérias/metabolismo , Bacteriófago T4/metabolismo , Bacteriófagos/fisiologia , Sistemas CRISPR-Cas/genética , Endonucleases/metabolismo , Escherichia coli/metabolismo , Nucleotídeos Cíclicos/metabolismo , Oligonucleotídeos , Pirimidinas/metabolismoRESUMO
Stimulator of interferon genes (STING) is an antiviral signalling protein that is broadly conserved in both innate immunity in animals and phage defence in prokaryotes1-4. Activation of STING requires its assembly into an oligomeric filament structure through binding of a cyclic dinucleotide4-13, but the molecular basis of STING filament assembly and extension remains unknown. Here we use cryogenic electron microscopy to determine the structure of the active Toll/interleukin-1 receptor (TIR)-STING filament complex from a Sphingobacterium faecium cyclic-oligonucleotide-based antiphage signalling system (CBASS) defence operon. Bacterial TIR-STING filament formation is driven by STING interfaces that become exposed on high-affinity recognition of the cognate cyclic dinucleotide signal c-di-GMP. Repeating dimeric STING units stack laterally head-to-head through surface interfaces, which are also essential for human STING tetramer formation and downstream immune signalling in mammals5. The active bacterial TIR-STING structure reveals further cross-filament contacts that brace the assembly and coordinate packing of the associated TIR NADase effector domains at the base of the filament to drive NAD+ hydrolysis. STING interface and cross-filament contacts are essential for cell growth arrest in vivo and reveal a stepwise mechanism of activation whereby STING filament assembly is required for subsequent effector activation. Our results define the structural basis of STING filament formation in prokaryotic antiviral signalling.