BioRxiv (2024)

Abstract

Immune systems must rapidly sense viral infections to initiate antiviral signaling and protect the host. Bacteria encode >100 distinct viral (phage) defense systems and each has evolved to sense crucial components or activities associated with the viral lifecycle. Here we used a high-throughput AlphaFold-multimer screen to discover that a bacterial NLR-related protein directly senses multiple phage proteins, thereby limiting immune evasion. Phages encoded as many as 5 unrelated activators that were predicted to bind the same interface of a C-terminal sensor domain. Genetic and biochemical assays confirmed activators bound to the bacterial NLR-related protein at high affinity, induced oligomerization, and initiated signaling. This work highlights how in silico strategies can identify complex protein interaction networks that regulate immune signaling across the tree of life.

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• [BlueSky]

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• BioRxiv preprint, December 17 2024,  

Citation

Emily M. Kibby, Laurel K. Robbins, Amar Deep, Nathan K. Min, Lindsay A. Whalen, Toni A. Nagy, Layla Freeborn, Kevin D. Corbett, Aaron T. Whiteley. A bacterial NLR-related protein recognizes multiple unrelated phage triggers to sense infection. bioRxiv 2024.12.17.629029; doi: https://doi.org/10.1101/2024.12.17.629029

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Nature (2024) PubMed PMID: 39020180; PubMed Central PMCID: .

Abstract

Ubiquitination pathways have crucial roles in protein homeostasis, signalling and innate immunity^1-3. In these pathways, an enzymatic cascade of E1, E2 and E3 proteins conjugates ubiquitin or a ubiquitin-like protein (Ubl) to target-protein lysine residues⁴. Bacteria encode ancient relatives of E1 and Ubl proteins involved in sulfur metabolism^5,6, but these proteins do not mediate Ubl-target conjugation, leaving open the question of whether bacteria can perform ubiquitination-like protein conjugation. Here we demonstrate that a bacterial operon associated with phage defence islands encodes a complete ubiquitination pathway. Two structures of a bacterial E1-E2-Ubl complex reveal striking architectural parallels with canonical eukaryotic ubiquitination machinery. The bacterial E1 possesses an amino-terminal inactive adenylation domain and a carboxy-terminal active adenylation domain with a mobile α-helical insertion containing the catalytic cysteine (CYS domain). One structure reveals a pre-reaction state with the bacterial Ubl C terminus positioned for adenylation, and a second structure mimics an E1-to-E2 transthioesterification state with the E1 CYS domain adjacent to the bound E2. We show that a deubiquitinase in the same pathway preprocesses the bacterial Ubl, exposing its C-terminal glycine for adenylation. Finally, we show that the bacterial E1 and E2 collaborate to conjugate Ubl to target-protein lysine residues. Together, these data reveal that bacteria possess bona fide ubiquitination systems with strong mechanistic and architectural parallels to canonical eukaryotic ubiquitination pathways, suggesting that these pathways arose first in bacteria.

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Citation

Chambers LR, Ye Q, Cai J, Gong M, Ledvina HE, Zhou H, Whiteley AT, Suhandynata RT, Corbett KD. Nature. 2024 Jul;631(8022):843-849. doi: 10.1038/s41586-024-07730-4. Epub 2024 Jul 17. PubMed PMID: 39020180; PubMed Central PMCID: PMC11476048.

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BioRxiv (2024). PubMed PMID: 38895412; PubMed Central PMCID: .

Abstract

Bacteria encode a wide range of antiphage systems and a subset of these proteins are homologous to components of the human innate immune system. Mammalian nucleotide-binding and leucine-rich repeat containing proteins (NLRs) and bacterial NLR-related proteins use a central NACHT domain to link detection of infection with initiation of an antimicrobial response. Bacterial NACHT proteins provide defense against both DNA and RNA phages. Here we determine the mechanism of RNA phage detection by the bacterial NLR-related protein bNACHT25 in E. coli. bNACHT25 was specifically activated by Emesvirus ssRNA phages and analysis of MS2 phage escaper mutants that evaded detection revealed a critical role for Coat Protein (CP). A genetic assay confirmed CP was sufficient to activate bNACHT25 but the two proteins did not directly interact. Instead, we found bNACHT25 requires the host chaperone DnaJ to detect CP. Our data suggest that bNACHT25 detects a wide range of phages by guarding a host cell process rather than binding a specific phage-derived molecule.

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• [Twitter]

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• BioRxiv Preprint, June 4 2024, 

Citation

Conte AN, Ridgeway SM, Ruchel ME, Kibby EM, Nagy TA, Whiteley AT. bioRxiv. 2024 Jun 4;. doi: 10.1101/2024.06.04.597415. PubMed PMID: 38895412; PubMed Central PMCID: PMC11185742.

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BioRxiv (2023) PubMed PMID: 37546940; PubMed Central PMCID: PMC10402079.

Abstract

The mammalian innate immune system uses cyclic GMP–AMP synthase (cGAS) to synthesize the cyclic dinucleotide 2′,3′-cGAMP during antiviral and antitumor immune responses. 2′,3′-cGAMP is a nucleotide second messenger that initiates inflammatory signaling by binding to and activating the stimulator of interferon genes (STING) receptor. Bacteria also encode cGAS/DncV-like nucleotidyltransferases (CD-NTases) that produce nucleotide second messengers to initiate antiviral (antiphage) signaling. Bacterial CD-NTases produce a wide range of cyclic oligonucleotides but have not been documented to produce 2′,3′-cGAMP. Here we discovered bacterial CD-NTases that produce 2′,3′-cGAMP to restrict phage replication. Bacterial 2′,3′-cGAMP binds to CD-NTase associated protein 14 (Cap14), a transmembrane protein of unknown function. Using electrophysiology, we show that Cap14 is a chloride-selective ion channel that is activated by 2′,3′-cGAMP binding. Cap14 adopts a modular architecture, with an N-terminal transmembrane domain and a C-terminal nucleotide-binding SAVED domain. Domain-swapping experiments demonstrated the Cap14 transmembrane region could be substituted with a nuclease, thereby generating a biosensor that is selective for 2′,3′-cGAMP. This study reveals that 2′,3′-cGAMP signaling extends beyond metazoa to bacteria. Further, our findings suggest that transmembrane proteins of unknown function in bacterial immune pathways may broadly function as nucleotide-gated ion channels.

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• BioRxiv Preprint, July 24 2023,

Citation

Tak U, Walth P, Whiteley AT. bioRxiv. 2023 Jul 24;. doi: 10.1101/2023.07.24.550367. PubMed PMID: 37546940; PubMed Central PMCID: PMC10402079.

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Cell (2023). PubMed PMID: 37160116; PubMed Central PMCID: .

Abstract

Bacteria use a wide range of immune pathways to counter phage infection. A subset of these genes shares homology with components of eukaryotic immune systems, suggesting that eukaryotes horizontally acquired certain innate immune genes from bacteria. Here, we show that proteins containing a NACHT module, the central feature of the animal nucleotide-binding domain and leucine-rich repeat containing gene family (NLRs), are found in bacteria and defend against phages. NACHT proteins are widespread in bacteria, provide immunity against both DNA and RNA phages, and display the characteristic C-terminal sensor, central NACHT, and N-terminal effector modules. Some bacterial NACHT proteins have domain architectures similar to the human NLRs that are critical components of inflammasomes. Human disease-associated NLR mutations that cause stimulus-independent activation of the inflammasome also activate bacterial NACHT proteins, supporting a shared signaling mechanism. This work establishes that NACHT module-containing proteins are ancient mediators of innate immunity across the tree of life.

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• [SBGrid]
• [Nature Reviews Microbiology]
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• BioRxiv Preprint, July 20 2022, 

Citation

Kibby EM, Conte AN, Burroughs AM, Nagy TA, Vargas JA, Whalen LA, Aravind L, Whiteley AT. Cell. 2023 May 25;186(11):2410-2424.e18. doi: 10.1016/j.cell.2023.04.015. Epub 2023 May 8. PubMed PMID: 37160116; PubMed Central PMCID: PMC10294775.

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Nature (2023) PubMed PMID: 36755092; PubMed Central PMCID:

Abstract

In all organisms, innate immune pathways sense infection and rapidly activate potent immune responses while avoiding inappropriate activation (autoimmunity). In humans, the innate immune receptor cyclic GMP–AMP synthase (cGAS) detects viral infection to produce the nucleotide second messenger cyclic GMP–AMP (cGAMP), which initiates stimulator of interferon genes (STING)-dependent antiviral signalling. Bacteria encode evolutionary predecessors of cGAS called cGAS/DncV-like nucleotidyltransferases (CD-NTases), which detect bacteriophage infection and produce diverse nucleotide second messengers. How bacterial CD-NTase activation is controlled remains unknown. Here we show that CD-NTase-associated protein 2 (Cap2) primes bacterial CD-NTases for activation through a ubiquitin transferase-like mechanism. A cryo-electron microscopy structure of the Cap2–CD-NTase complex reveals Cap2 as an all-in-one ubiquitin transferase-like protein, with distinct domains resembling eukaryotic E1 and E2 proteins. The structure captures a reactive-intermediate state with the CD-NTase C terminus positioned in the Cap2 E1 active site and conjugated to AMP. Cap2 conjugates the CD-NTase C terminus to a target molecule that primes the CD-NTase for increased cGAMP production. We further demonstrate that a specific endopeptidase, Cap3, balances Cap2 activity by cleaving CD-NTase–target conjugates. Our data demonstrate that bacteria control immune signalling using an ancient, minimized ubiquitin transferase-like system and provide insight into the evolution of the E1 and E2 machinery across domains of life.

News and Commentaries 

• Scientists discover more bacterial tools that could be reprogrammed to treat human disease [Å·ÃÀ¿Ú±¬ÊÓƵ Boulder Today]
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• BioRxiv Preprint, March 31 2022,

Citation

Ledvina HE, Ye Q, Gu Y, Sullivan AE, Quan Y, Lau RK, Zhou H, Corbett KD, Whiteley AT. Nature. 2023 Apr;616(7956):319-325. doi: 10.1038/s41586-022-05647-4. Epub 2023 Feb 8. PubMed PMID: 36755092; PubMed Central PMCID: PMC10292035.

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