Biology subjects

Whiteley, A. T.

Publications and source records attributed to Whiteley, A. T..

3 recordsLinked to original sources

bioRxiv2022

Bacterial NLR-related proteins protect against phage

Bacteria use a wide range of immune systems to counter phage infection. A subset of these genes share 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 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.

microbiology↗

bioRxiv2022

cGASylation by a bacterial E1-E2 fusion protein primes antiviral immune signaling

In all organisms, innate immune pathways sense viral infection and rapidly activate potent immune responses while maintaining a high degree of specificity to prevent inappropriate activation (autoimmunity). In humans, the innate-immune receptor cGAS detects viral infection to produce the nucleotide second messenger cGAMP, which initiates STING-dependent antiviral signaling. Bacteria encode predecessors of the cGAS-STING pathway, termed cyclic oliogonucleotide-based antiphage signaling systems (CBASS), and bacterial cGAS detects bacteriophage infection to produce cGAMP. How bacterial cGAS activation is controlled, however, remains unknown. Here, we show that the CBASS-associated protein Cap2 primes bacterial cGAS for activation through a ubiquitin transferase-like mechanism. A cryoelectron microscopy structure of the Cap2-cGAS complex reveals Cap2 as an all-in-one ubiquitin transferase-like protein, with distinct domains resembling the eukaryotic E1 protein ATG7 and the E2 proteins ATG10 and ATG3. The structure captures a reactive-intermediate state with the cGAS C-terminus extending into the Cap2 E1 active site and conjugated to AMP. We find that Cap2 ligates the cGAS C-terminus to a target molecule in cells, a process we call cGASylation. cGASylation primes cGAS for a [~]50-fold increase in cGAMP production. We further demonstrate that Cap2 activity is balanced by a specific endopeptidase, Cap3, which deconjugates cGAS and antagonizes antiviral signaling. Our data demonstrate that bacteria control immune signaling using an ancient, minimized ubiquitin transferase-like system and provide insight into the evolution of E1 and E2 machinery across the kingdoms of life.

microbiology↗

bioRxiv2019

Structure and mechanism of a cyclic trinucleotide-activated bacterial endonuclease mediating bacteriophage immunity

Bacteria possess an array of defenses against foreign invaders, including diverse nucleases that target and destroy the genome of an invading bacteriophage or foreign DNA element. A recently-described bacteriophage immunity pathway employs a cGAS/DncV-like nucleotidyltransferase to produce a cyclic tri-AMP second messenger, which activates the DNA endonuclease effector NucC. Here, we show that NucC is related to restriction enzymes but uniquely assembles into a homotrimer in solution. cAAA binding in a conserved allosteric pocket promotes assembly of two NucC trimers into a homohexamer competent for double-strand DNA cleavage. We propose that NucC mediates bacteriophage immunity either through global activation, causing altruistic cell death and abortive infection, or through local activation and targeted phage genome destruction. Finally, we identify NucC homologs in type III CRISPR-Cas systems, where they likely function as accessory nucleases activated by cyclic oligoadenylate second messengers synthesized by these systems effector complexes.

biochemistry↗