Marcos Pires

Nature, Published online: 11 March 2020; doi:10.1038/s41586-020-2079-1

In mouse models of cancer, a biorthogonal chemical system based on desilylation catalysed by phenylalanine trifluoroborate enables the controlled release of gasdermin to induce pyroptosis selectively in tumour cells

Kagan and Fitzgerald comprehensively review the functions and mechanisms of Toll-like receptors (TLRs), which are crucial detectors of microbial biomolecules and mediators of cellular immunity. They synthesize the overarching themes that have emerged from TLR signaling but are repeated throughout the pattern recognition receptor (PRR) superfamily.

ABSTRACT

Frequent and excessive use of antibiotics primes patients to Clostridioides difficile infection (CDI), which leads to fatal pseudomembranous colitis, with limited treatment options. In earlier reports, we used a drug repurposing strategy and identified amoxapine (an antidepressant), doxapram (a breathing stimulant), and trifluoperazine (an antipsychotic), which provided significant protection to mice against lethal infections with several pathogens, including C. difficile. However, the mechanisms of action of these drugs were not known. Here, we provide evidence that all three drugs offered protection against experimental CDI by reducing bacterial burden and toxin levels, although the drugs were neither bacteriostatic nor bactericidal in nature and had minimal impact on the composition of the microbiota. Drug-mediated protection was dependent on the presence of the microbiota, implicating its role in evoking host defenses that promoted protective immunity. By utilizing transcriptome sequencing (RNA-seq), we identified that each drug increased expression of several innate immune response-related genes, including those involved in the recruitment of neutrophils, the production of interleukin 33 (IL-33), and the IL-22 signaling pathway. The RNA-seq data on selected genes were confirmed by quantitative real-time PCR (qRT-PCR) and protein assays. Focusing on amoxapine, which had the best anti-CDI outcome, we demonstrated that neutralization of IL-33 or depletion of neutrophils resulted in loss of drug efficacy. Overall, our lead drugs promote disease alleviation and survival in the murine model through activation of IL-33 and by clearing the pathogen through host defense mechanisms that critically include an early influx of neutrophils.

IMPORTANCE Clostridioides difficile is a spore-forming anaerobic bacterium and the leading cause of antibiotic-associated colitis. With few therapeutic options and high rates of disease recurrence, the need to develop new treatment options is urgent. Prior studies utilizing a repurposing approach identified three nonantibiotic Food and Drug Administration-approved drugs, amoxapine, doxapram, and trifluoperazine, with efficacy against a broad range of human pathogens; however, the protective mechanisms remained unknown. Here, we identified mechanisms leading to drug efficacy in a murine model of lethal C. difficile infection (CDI), advancing our understanding of the role of these drugs in infectious disease pathogenesis that center on host immune responses to C. difficile. Overall, these studies highlight the crucial involvement of innate immune responses, as well as the importance of immunomodulation as a potential therapeutic option to combat CDI.

Intestinal bile acids are known to modulate the germination and growth of Clostridioides difficile. Here we describe a role for intestinal bile acids in directly binding and neutralizing TcdB toxin, the primary determinant of C. difficile disease. We show that individual primary and secondary bile acids reversibly bind and inhibit...

Particularly with the recent outbreak of coronavirus disease 2019 (COVID-19), viruses have a bad reputation these days. However, it is important to note that viruses come in many types and can infect not only humans but almost all life forms, and their infections are not always detrimental to the host....

Nature Communications, Published online: 10 March 2020; doi:10.1038/s41467-020-14336-7

Cell surface proteins mediate the interactions between cells and their extracellular environment. Here the authors design synthetic biomemetic receptor-like sensors that facilitate programmable interactions between bacteria and their target.

Nature, Published online: 04 March 2020; doi:10.1038/s41586-020-2066-6

In response to infection with Staphylococcus aureus in vitro and in vivo, host cells increase their secretion of exosomes containing ADAM10—vesicular structures that can provide protection by sequestering bacterial toxins.

In oval-shaped Streptococcus pneumoniae, septal and longitudinal peptidoglycan syntheses are performed by independent functional complexes: the divisome and the elongasome. Penicillin-binding proteins (PBPs) were long considered the key peptidoglycan-synthesizing enzymes in these complexes. Among these were the bifunctional class A PBPs, which are both glycosyltransferases and transpeptidases, and monofunctional class...

ABSTRACT

Synthesis and cleavage of the cell wall polymer peptidoglycan (PG) are carefully orchestrated processes and are essential for the growth and survival of bacteria. Yet, the function and importance of many enzymes that act on PG in Mycobacterium tuberculosis remain to be elucidated. We demonstrate that the activity of the N-acetylmuramyl-l-alanine amidase Ami1 is dispensable for cell division in M. tuberculosis in vitro yet contributes to the bacterium’s ability to persist during chronic infection in mice. Furthermore, the d,l-endopeptidase RipA, a predicted essential enzyme, is dispensable for the viability of M. tuberculosis but required for efficient cell division in vitro and in vivo. Depletion of RipA sensitizes M. tuberculosis to rifampin and to cell envelope-targeting antibiotics. Ami1 helps sustain residual cell division in cells lacking RipA, but the partial redundancy provided by Ami1 is not sufficient during infection, as depletion of RipA prevents M. tuberculosis from replicating in macrophages and leads to dramatic killing of the bacteria in mice. Notably, RipA is essential for persistence of M. tuberculosis in mice, suggesting that cell division is required during chronic mouse infection. Despite the multiplicity of enzymes acting on PG with redundant functions, we have identified two PG hydrolases that are important for M. tuberculosis to replicate and persist in the host.

IMPORTANCE Tuberculosis (TB) is a major global heath burden, with 1.6 million people succumbing to the disease every year. The search for new drugs to improve the current chemotherapeutic regimen is crucial to reducing this global health burden. The cell wall polymer peptidoglycan (PG) has emerged as a very successful drug target in bacterial pathogens, as many currently used antibiotics target the synthesis of this macromolecule. However, the multitude of genes encoding PG-synthesizing and PG-modifying enzymes with apparent redundant functions has hindered the identification of novel drug targets in PG synthesis in Mycobacterium tuberculosis. Here, we demonstrate that two PG-cleaving enzymes are important for virulence of M. tuberculosis. In particular, the d,l-endopeptidase RipA represents a potentially attractive drug target, as its depletion results in the clearance of M. tuberculosis from the host and renders the bacteria hypersusceptible to rifampin, a frontline TB drug, and to several cell wall-targeting antibiotics.

Antimicrobials on tap: The stilbene tapinarof, a drug used to treat inflammatory skin diseases, is transformed into two novel dimers in Photorhabdus. A cupin enzyme contributes to the oxidative dimerization of tapinarof and other dietary stilbenes. While tapinarof significantly reduces severe colitis symptoms in a mouse model, the dimers display antimicrobial activity against Mycobacterium and the antibiotic‐resistant pathogens MRSA and VRE.

Abstract

Tapinarof is a stilbene drug that is used to treat psoriasis and atopic dermatitis, and is thought to function through regulation of the AhR and Nrf2 signaling pathways, which have also been linked to inflammatory bowel diseases. It is produced by the gammaproteobacterial Photorhabdus genus, which thus represents a model to probe tapinarof structural and functional transformations. We show that Photorhabdus transforms tapinarof into novel drug metabolism products that kill inflammatory bacteria, and that a cupin enzyme contributes to the conversion of tapinarof and related dietary stilbenes into novel dimers. One dimer has activity against methicillin‐resistant Staphylococcus aureus (MRSA) and vancomycin‐resistant Enterococcus faecalis (VRE), and another undergoes spontaneous cyclizations to a cyclopropane‐bridge‐containing hexacyclic framework that exhibits activity against Mycobacterium. These dimers lack efficacy in a colitis mouse model, whereas the monomer reduces disease symptoms.

Nature, Published online: 26 February 2020; doi:10.1038/s41586-020-2047-9

Metabolomics data from germ-free and specific-pathogen-free mice reveal effects of the microbiome on host chemistry, identifying conjugations of bile acids that are also enriched in patients with inflammatory bowel disease or cystic fibrosis.

Secondary bile acids (SBAs) are some of the most concentrated bacterially derived gut metabolites. Sinha et al. find UC pouch patients have reduced SBAs and Ruminococcaceae (one of the few SBA-producing taxa) compared with FAP-control patients. In colitis models, SBAs ameliorate disease in a process reliant on the TGR5 bile acid receptor.

Nature Medicine, Published online: 24 February 2020; doi:10.1038/s41591-020-0761-3

Microscopy and 16S rRNA sequencing suggest that there is a limited bacterial presence in the human fetal intestine, with one enriched Micrococcus species exhibiting immunomodulatory activity ex vivo.

Nature Immunology, Published online: 17 February 2020; doi:10.1038/s41590-020-0602-z

The gut microbiota and their proximate immune cells engage in a dialog of reciprocal regulation. James and colleagues describe how immune cell and microbiotal populations vary along the length of the human colon.

Nature Microbiology, Published online: 17 February 2020; doi:10.1038/s41564-019-0634-z

An observational human clinical trial using a bacteriophage preparation showed that it was well tolerated without major adverse events in human patients with Staphylococcus aureus septicaemia.

Nature Medicine, Published online: 17 February 2020; doi:10.1038/s41591-020-0764-0

In germ-free mice colonized with human microbiota, mucosal IL-22 signaling promotes the growth of succinate-consuming commensal bacteria via host mucus glycosylation, and transplantation of these bacteria limits Clostridioides difficile infection.

A native‐chemical‐ligation‐assisted diaminodiacid strategy was developed for the chemical synthesis of peptide disulfide surrogates, forming ring sizes of up to 50 amino acids. The method can facilitate the engineering of biologically interesting disulfide‐containing peptides, and may widen the horizon of peptide‐based research tools and diagnostic or therapeutic reagents.

Abstract

The use of synthetic bridges as surrogates for disulfide bonds has emerged as a practical strategy to obviate the poor stability of some disulfide‐containing peptides. However, peptides incorporating large‐span synthetic bridges are still beyond the reach of existing methods. Herein, we report a native chemical ligation (NCL)‐assisted diaminodiacid (DADA) strategy that enables the robust generation of disulfide surrogate peptides incorporating surrogate bridges up to 50 amino acids in length. This strategy provides access to some highly desirable but otherwise impossible‐to‐obtain disulfide surrogates of bioactive peptide. The bioactivities and structures of the synthetic disulfide surrogates were verified by voltage clamp assays, NMR, and X‐ray crystallography; and stability studies established that the disulfide replacements effectively overcame the problems of disulfide reduction and scrambling that often plague these pharmacologically important peptides.

Effector-triggered immunity (ETI), induced by host immune receptors in response to microbial effectors, protects plants against virulent pathogens. However, a systematic study of ETI prevalence against species-wide pathogen diversity is lacking. We constructed the Pseudomonas syringae Type III Effector Compendium (PsyTEC) to reduce the pan-genome complexity of 5127 unique effector proteins, distributed among 70 families from 494 strains, to 529 representative alleles. We screened PsyTEC on the model plant Arabidopsis thaliana and identified 59 ETI-eliciting alleles (11.2%) from 19 families (27.1%), with orthologs distributed among 96.8% of P. syringae strains. We also identified two previously undescribed host immune receptors, including CAR1, which recognizes the conserved effectors AvrE and HopAA1, and found that 94.7% of strains harbor alleles predicted to be recognized by either CAR1 or ZAR1.

In this Primer, Pratt & Parker overview the biological applications of “click chemistry,” a class of small-molecule reactions that can efficiently conjugate substrates to specific biomolecules. Focusing on proteomic investigations, they provide insight into the biological questions where it may be most useful, including studies of post-translational modifications and protein-protein, protein-drug, and protein-metabolite interactions.

Nature Chemical Biology, Published online: 10 February 2020; doi:10.1038/s41589-020-0467-3

A covalent pan-inhibitor of bacterial bile salt hydrolases developed by adding a chenodeoxycholic acid moiety to the warhead is not bactericidal and is therefore useful for studying the effects of bile acids on host physiology.

When nutrients in their environment are exhausted, bacterial cells become arrested for growth. During these periods, a primary challenge is maintaining cellular integrity with a reduced capacity for renewal or repair. Here, we show that the heat-shock protease FtsH is generally required for growth arrest survival of Pseudomonas aeruginosa, and...