VapC proteins from Mycobacterium tuberculosis share ribonuclease sequence specificity but differ in regulation and toxicity

Iron-restricted Mycobacterium tuberculosis exports pathogenicity factors packed in extracellular vesicles

Mycobacterium tuberculosis, the pathogen responsible for human tuberculosis, responds to iron limitation by increasing the production of extracellular vesicles. This study examined the protein composition of induced M. tuberculosis extracellular membrane vesicles using chromatography coupled with mass spectrometry. The results revealed that vesicles contain key pathogenicity factors, including proteins that enhance bacterial survival, immune evasion, and inflammation. These findings deepen our understanding of the potential role of extracellular vesicles in M. tuberculosis-host interactions. The data can also aid in identifying new biomarkers of infection and developing vesicle-based, culture-independent TB diagnostic platforms.

Understanding the physiological role and cross-interaction network of VapBC35 toxin-antitoxin system from Mycobacterium tuberculosis

The VapBC toxin-antitoxin (TA) system, composed of VapC toxin and VapB antitoxin, has gained attention due to its relative abundance in members of the M. tuberculosis complex. Here, we have functionally characterised VapBC35 TA system from M. tuberculosis. We show that ectopic expression of VapC35 inhibits M. smegmatis growth in a bacteriostatic manner. Also, an increase in the VapB35 antitoxin to VapC35 toxin ratio results in a stronger binding affinity of the complex with the promoter-operator DNA. We show that VapBC35 is necessary for M. tuberculosis adaptation in oxidative stress conditions but is dispensable for M. tuberculosis growth in guinea pigs. Further, using a combination of co-expression studies and biophysical methods, we report that VapC35 also interacts with non-cognate antitoxin VapB3. Taken together, the present study advances our understanding of cross-interaction networks among VapBC TA systems from M. tuberculosis.

Comparative Genomics Reveal Distinct Environment Preference and Functional Adaptation Among Lineages of Gemmatimonadota

Bacteria in the phylum Gemmatimonadota are globally distributed and abundant in microbial communities of various environments, playing an important role in driving biogeochemical cycling on Earth. Although high diversities in taxonomic composition and metabolic capabilities have been reported, little is known about the environmental preferences and associated functional features that facilitate adaptation among different Gemmatimonadota lineages. This study systematically analyzed the relationships between the environments, taxonomy, and functions of Gemmatimonadota lineages, by using a comparative genomics approach based on 1356 Gemmatimonadota genomes (213 high-quality and non-redundant genomes) available in a public database (NCBI). The taxonomic analysis showed that the 99.5% of the genomes belong to the class Gemmatimonadetes, and the rest of the genomes belong to the class Glassbacteria. Functional profiling revealed clear environmental preference among different lineages of Gemmatimonadota, and a marine group and two non-marine groups were identified and tested to be significantly different in functional composition. Further annotation and statistical comparison revealed a large number of functional genes (e.g., amiE, coxS, yfbK) that were significantly enriched in genomes from the marine group, supporting enhanced capabilities in energy acquisition, genetic information regulation (e.g., DNA repair), electrolyte homeostasis, and growth rate control. These genomic features are important for their survival in the marine environment, which is oligotrophic, variable, and with high salinity. The findings enhanced our understanding of the metabolic processes and environmental adaptation of Gemmatimonadota, and further advanced the understanding of the interactions of microorganisms and their habitats.

Phosphorylation of VapB antitoxins affects intermolecular interactions to regulate VapC toxin activity in Mycobacterium tuberculosis

Toxin-antitoxin modules are present in many bacterial pathogens. The VapBC family is particularly abundant in members of the Mycobacterium tuberculosis complex, with 50 modules present in the M. tuberculosis genome. In type IIA modules, the VapB antitoxin protein binds to and inhibits the activity of the co-expressed cognate VapC toxin protein. VapB proteins may also bind to promoter region sequences and repress the expression of the vapB-vapC operon. Though VapB-VapC interactions can control the amount of free VapC toxin in the bacterial cell, the mechanisms that affect this interaction are poorly understood. Based on our recent finding of Ser/Thr phosphorylation of VapB proteins in M. tuberculosis, we substituted phosphomimetic or phosphoablative amino acids at the phosphorylation sites of two VapB proteins. We found that phosphomimetic substitution of VapB27 and VapB46 resulted in decreased interaction with their respective cognate VapC proteins, whereas phosphoablative substitution did not alter binding. Similarly, we determined that phosphomimetic substitution interfered with VapB binding to promoter region DNA sequences. Both decreased VapB-VapC interaction and decreased VapB repression of vapB-vapC operon transcription would result in increased free VapC in the M. tuberculosis cell. In growth inhibition experiments, M. tuberculosis strains expressing vapB46-vapC46 constructs containing a phosphoablative vapB mutation resulted in lower toxicity compared to a strain expressing native vapB46, whereas similar or greater toxicity was observed in the strain expressing the phosphomimetic vapB mutation. These results identify a novel mechanism by which VapC toxicity activity can be regulated by VapB phosphorylation.IMPORTANCEIntracellular bacterial toxins are present in many bacterial pathogens and have been linked to bacterial survival in response to stresses encountered during infection. The activity of many toxins is regulated by a co-expressed antitoxin protein that binds to and sequesters the toxin protein. The mechanisms by which an antitoxin may respond to stresses to alter toxin activity are poorly understood. Here, we show that antitoxin interactions with its cognate toxin and with promoter DNA required for antitoxin and toxin expression can be altered by Ser/Thr phosphorylation of the antitoxin and, thus, affect toxin activity. This reversible modification may play an important role in regulating toxin activity within the bacterial cell in response to signals generated during infection.

Deciphering the role of VapBC toxin-antitoxin systems in Mycobacterium tuberculosis stress adaptation

Mycobacterium tuberculosis (Mtb) harbors a high number of Toxin-Antitoxin (TA) systems, wherein half of them belong to virulence associated proteins B and C (VapBC) family that has a characteristic PilT N-terminus domain and ribonuclease activity. Functional insights into Mtb VapBC TA modules unraveled their role in adaptation to various host-mediated stressors, including oxidative/nitrosative, chemical and nutrient starvation as well as multidrug tolerance and establishment of persistence. To understand the intricacies of Mtb's pathogenesis, absolute cellular targets of 19 VapC(s) were determined. Some exhibit a shared ribonuclease activity, whereas others harbor tRNAse and 23S rRNA cleavage activity. The detailed functional characterization of VapBC4, VapBC12 and VapBC22, including in vivo deletion mutant studies revealed their role in Mtb's virulence/persistence. For example, the VapC22 mutant was attenuated for Mtb's growth in mice and elicited a decreased TH1 response, whereas mice infected with VapC12 mutant displayed a substantially higher bacillary load and pro-inflammatory response than the wild type, showing a hyper-virulent phenotype. Further experimental studies are needed to decode the functional role of VapBC systems and unravel their cellular targets. Taken together, Mtb VapBC TA systems seem to be promising drug targets owing to their key role in enduring stressors, antibiotic resistance and persistence.

Phosphorylation of VapB antitoxins affects intermolecular interactions to regulate VapC toxin activity in Mycobacterium tuberculosis

Toxin-antitoxin modules are present in many bacterial pathogens. The VapBC family is particularly abundant in members of the Mycobacterium tuberculosis complex, with 50 modules present in the M. tuberculosis genome. In type IIA modules the VapB antitoxin protein binds to and inhibits the activity of the co-expressed cognate VapC toxin protein. VapB proteins also bind to promoter region sequences and repress expression of the vapB-vapC operon. Though VapB-VapC interactions can control the amount of free VapC toxin in the bacterial cell, the mechanisms that affect this interaction are poorly understood. Based on our recent finding of Ser/Thr phosphorylation of VapB proteins in M. tuberculosis, we substituted phosphomimetic or phosphoablative amino acids at the phosphorylation sites of two VapB proteins. We found that phosphomimetic substitution of VapB27 and VapB46 resulted in decreased interaction with their respective cognate VapC proteins, whereas phosphoablative substitution did not alter binding. Similarly, we determined that phosphomimetic substitution interfered with VapB binding to promoter region DNA sequences. Both decreased VapB-VapC interaction and decreased VapB repression of vapB-vapC operon transcription would result in increased free VapC in the M. tuberculosis cell. M. tuberculosis strains expressing vapB46-vapC46 constructs containing a phosphoablative vapB mutation resulted in lower toxicity compared to a strain expressing native vapB46, whereas similar or greater toxicity was observed in the strain expressing the phosphomimetic vapB mutation. These results identify a novel mechanism by which VapC toxicity activity can be regulated by VapB phosphorylation, potentially in response to extracytoplasmic as well as intracellular signals.

A novel enzyme-linked ligand-sorbent assay (ELLSA) to screening pulmonary tuberculosis: a retrospective cross-sectional study

BACKGROUND

Little knowledge of antigen existence in the pulmonary tuberculosis (PTB) patient serum impeded its development in antigen detection technology, despite its considerable potential.

METHODS

Human ligand proteins and their adsorbent Mycobacterium tuberculosis (M.tb) proteins in the serum of PTB patients were identified using human protein chip (HuProt™) and LC-MS/MS, successively. The monoclonal antibody of ligand proteins, C5orf24, and polyclonal antibody of 9 M.tb proteins were prepared on mice and rabbits which were used to develop a novel enzyme-linked ligand-sorbent assay (ELLSA). The 412 volunteers were divided into the PTB group (n = 250) and the healthy control (n = 162). The PTB group was further divided into ATB (n = 131), LTBI (n = 18), Clinical diagnosis (n = 18), and Suspected (n = 73). All samples were tested by ELLSA to evaluate the diagnostic performance of ELLSA in PTB patients.

RESULTS

Nine ligand proteins specific to PTB patients were identified on chips, with Chromosome 5 Open Reading Frame 24 (C5orf24) and kinocilin (KNCN) showing significantly higher signals. Proteomic analysis of the C5orf24-and KNCN-adsorbent protein complexes revealed 10 and 10 of the M.tb proteins, respectively. According to the composition reference of standard, the ELLSA based on C5orf24 ligand demonstrated a higher sensitivity of 69.6% and specificity of 90.18% in ATB patients and had a sensitivity of 64.22% in bacterial negative pulmonary tuberculosis, whereas the sensitivity of MGIT 960 and Xpert M.tb/RIF were 0%, respectively.

CONCLUSIONS

M.tb proteins in serum can be enriched by ligand proteins and detected by ELLSA which proved to have excellent diagnostic performance for PTB.

Toxin-Antitoxin system of Mycobacterium tuberculosis: Roles beyond stress sensor and growth regulator

The advent of effective drug regimen and BCG vaccine has significantly decreased the rate of morbidity and mortality of TB. However, lengthy treatment and slower recovery rate, as well as reactivation of the disease with the emergence of multi-drug, extensively-drug, and totally-drug resistance strains, pose a serious concern. The complexities associated are due to the highly evolved and complex nature of the bacterium itself. One of the unique features of Mycobacterium tuberculosis [M.tb] is that it has undergone reductive evolution while maintaining and amplified a few gene families. One of the critical gene family involved in the virulence and pathogenesis is the Toxin-Antitoxin system. These families are believed to harbor virulence signature and are strongly associated with various stress adaptations and pathogenesis. The M.tb TA systems are linked with growth regulation machinery during various environmental stresses. The genes of TA systems are differentially expressed in the host during an active infection, oxidative stress, low pH stress, and starvation, which essentially indicate their role beyond growth regulators. Here in this review, we have discussed different roles of TA gene families in various stresses and their prospective role at the host-pathogen interface, which could be exploited to understand the M.tb associated pathomechanisms better and further designing the new strategies against the pathogen.

DosR's multifaceted role on Mycobacterium bovis BCG revealed through multi-omics

Mycobacterium tuberculosis (Mtb) is an intracellular bacterium that causes a highly contagious and potentially lethal tuberculosis (TB) in humans. It can maintain a dormant TB infection within the host. DosR (dormancy survival regulator) (Rv3133c) has been recognized as one of the key transcriptional proteins regulating bacterial dormancy and participating in various metabolic processes. In this study, we extensively investigate the still not well-comprehended role and mechanism of DosR in Mycobacterium bovis (M. bovis) Bacillus Calmette-Guérin (BCG) through a combined omics analysis. Our study finds that deleting DosR significantly affects the transcriptional levels of 104 genes and 179 proteins. Targeted metabolomics data for amino acids indicate that DosR knockout significantly upregulates L-Aspartic acid and serine synthesis, while downregulating seven other amino acids, including L-histidine and lysine. This suggests that DosR regulates amino acid synthesis and metabolism. Taken together, these findings provide molecular and metabolic bases for DosR effects, suggesting that DosR may be a novel regulatory target.

Heat shock response in Sulfolobus acidocaldarius and first implications for cross-stress adaptation

Sulfolobus acidocaldarius, a thermoacidophilic crenarchaeon, frequently encounters temperature fluctuations, oxidative stress, and nutrient limitations in its environment. Here, we employed a high-throughput transcriptomic analysis to examine how the gene expression of S. acidocaldarius changes when exposed to high temperatures (92 °C). The data obtained was subsequently validated using quantitative reverse transcription-PCR (qRT-PCR) analysis. Our particular focus was on genes that are involved in the heat shock response, type-II Toxin-Antitoxin systems, and putative transcription factors. To investigate how S. acidocaldarius adapts to multiple stressors, we assessed the expression of these selected genes under oxidative and nutrient stresses using qRT-PCR analysis. The results demonstrated that the gene thβ encoding the β subunit of the thermosome, as well as hsp14 and hsp20, play crucial roles in the majority of stress conditions. Furthermore, we observed overexpression of at least eight different TA pairs belonging to the type II TA systems under all stress conditions. Additionally, four common transcription factors: FadR, TFEβ, CRISPR loci binding protein, and HTH family protein were consistently overexpressed across all stress conditions, indicating their significant role in managing stress. Overall, this work provides the first insight into molecular players involved in the cross-stress adaptation of S. acidocaldarius.

Impact of Genomic Deletion RD16 on the Expression of the Mycobacterium bovis BCG Moreau VapBC47 Toxin-Antitoxin System

Mycobacterium bovis BCG is the only vaccine against tuberculosis. The variable forms of cultivation throughout the years, before seed-lots were developed, allowed in vitro evolution of the original strain, generating a family of vaccines with different phenotypic and genotypic characteristics. Molecular studies revealed regions of difference (RDs) in the genomes of the various BCG strains. This work aims to characterize the gene pair rv3407-rv3408 (vapB47-vapC47), coding for a toxin-antitoxin system of the VapBC family, and to evaluate possible transcriptional effects due to the adjacent BCG Moreau-specific genomic deletion RD16. We show that these genes are co-transcribed in BCG strains Moreau and Pasteur, and that the inactivation of an upstream transcriptional repressor (Rv3405c) due to RD16 has a polar effect, leading to increased vapBC47 expression. Furthermore, we detect VapB47 DNA binding in vitro, dependent on a 5' vapB47 sequence that contributes to a palindrome, spanning the promoter and coding region. Our data shed light on the regulation of VapBC systems and on the impact of the BCG Moreau RD16 deletion in the expression of adjacent genes, contributing to a better understanding of BCG Moreau physiology.

Structural insights into DarT toxin neutralization by cognate DarG antitoxin: ssDNA mimicry by DarG C-terminal domain keeps the DarT toxin inhibited

In the DarTG toxin-antitoxin system, the DarT toxin ADP-ribosylates single-stranded DNA (ssDNA), which stalls DNA replication and plays a crucial role in controlling bacterial growth and bacteriophage infection. This toxic activity is reversed by the N-terminal macrodomain of the cognate antitoxin DarG. DarG also binds DarT, but the role of these interactions in DarT neutralization is unknown. Here, we report that the C-terminal domain of DarG (DarG toxin-binding domain [DarGTBD]) interacts with DarT to form a 1:1 stoichiometric heterodimeric complex. We determined the 2.2 Å resolution crystal structure of the Mycobacterium tuberculosis DarT-DarGTBD complex. The comparative structural analysis reveals that DarGTBD interacts with DarT at the DarT/ssDNA interaction interface, thus sterically occluding substrate ssDNA binding and consequently inactivating toxin by direct protein-protein interactions. Our data support a unique two-layered DarT toxin neutralization mechanism of DarG, which is important in keeping the toxin molecules in check under normal growth conditions.

Functional characterization of toxin-antitoxin system in Mycobacterium tuberculosis

Toxin-Antitoxin (TA) system is abundant in the microbial genome, especially in bacteria and archaea. Its genetic elements and addiction modules with the role of bacterial persistence and virulence. The TA system consists of a toxin and most unstable antitoxin that could be a protein or non-encoded RNA, TA loci are chromosomally determined and their cellular functions are mostly unknown. Approximately 93 TA systems were demonstrated and more functionally available in M. tuberculosis (Mtb), the organism responsible for tuberculosis (TB). It is an airborne disease, which is causing ill-health to humans. M. tuberculosis possesses higher TA loci than other microbes and non-tubercle bacilli, the following TA types have been identified such as VapBC, MazEF, HigBA, RelBE, ParDE, DarTG, PemIK, MbcTA, and one tripartite type II TAC-Chaperone system. Toxin-antitoxin Database (TADB) brings a detailed update on Toxin-Antitoxin classification in the different pathogens such as staphylococcus aureus, streptococcus pneumonia, Vibrio cholerae, Salmonella typhimurium, Shigella flexneri, and helicobacter pylori, etc. So, this Toxin-Antitoxin system is a master regulator for bacterial growth, and an essential factor in analyzing the properties and function of disease persistence, biofilm formation, and pathogenicity. The TA system is an advanced tool to develop a new therapeutic agent against M. tuberculosis.

Das Gupta S. Apoptosis like symptoms associated with abortive infection of Mycobacterium smegmatis by mycobacteriophage D29

Mycobacteriophages are phages that infect mycobacteria resulting in their killing. Although lysis is the primary mechanism by which mycobacteriophages cause cell death, others such as abortive infection may also be involved. We took recourse to perform immunofluorescence and electron microscopic studies using mycobacteriophage D29 infected Mycobacterium smegmatis cells to investigate this issue. We could observe the intricate details of the infection process using these techniques such as adsorption, the phage tail penetrating the thick mycolic acid layer, formation of membrane pores, membrane blebbing, and phage release. We observed a significant increase in DNA fragmentation and membrane depolarization using cell-biological techniques symptomatic of programmed cell death (PCD). As Toxin-Antitoxin (TA) systems mediate bacterial PCD, we measured their expression profiles with and without phage infection. Of the three TAs examined, MazEF, VapBC, and phd/doc, we found that in the case of VapBC, a significant decrease in the antitoxin (VapB): toxin (VapC) ratio was observed following phage infection, implying that high VapC may have a role to play in the induction of mycobacterial apoptotic cell death following phage infection. This study indicates that D29 infection causes mycobacteria to undergo morphological and molecular changes that are hallmarks of apoptotic cell death.

Innate Immune Responses of Galleria mellonella to Mycobacterium bovis BCG Challenge Identified Using Proteomic and Molecular Approaches

The larvae of the insect Galleria mellonella, have recently been established as a non-mammalian infection model for the Mycobacterium tuberculosis complex (MTBC). To gain further insight into the potential of this model, we applied proteomic (label-free quantification) and transcriptomic (gene expression) approaches to characterise the innate immune response of G. mellonella to infection with Mycobacterium bovis BCG lux over a 168 h time course. Proteomic analysis of the haemolymph from infected larvae revealed distinct changes in the proteome at all time points (4, 48, 168 h). Reverse transcriptase quantitative PCR confirmed induction of five genes (gloverin, cecropin, IMPI, hemolin, and Hdd11), which encoded proteins found to be differentially abundant from the proteomic analysis. However, the trend between gene expression and protein abundance were largely inconsistent (20%). Overall, the data are in agreement with previous phenotypic observations such as haemocyte internalization of mycobacterial bacilli (hemolin/β-actin), formation of granuloma-like structures (Hdd11), and melanization (phenoloxidase activating enzyme 3 and serpins). Furthermore, similarities in immune expression in G. mellonella, mouse, zebrafish and in vitro cell-line models of tuberculosis infection were also identified for the mechanism of phagocytosis (β-actin). Cecropins (antimicrobial peptides), which share the same α-helical motif as a highly potent peptide expressed in humans (h-CAP-18), were induced in G. mellonella in response to infection, giving insight into a potential starting point for novel antimycobacterial agents. We believe that these novel insights into the innate immune response further contribute to the validation of this cost-effective and ethically acceptable insect model to study members of the MTBC.

Depletion of the DarG antitoxin in Mycobacterium tuberculosis triggers the DNA-damage response and leads to cell death

Of the ~80 putative toxin-antitoxin (TA) modules encoded by the bacterial pathogen Mycobacterium tuberculosis (Mtb), three contain antitoxins essential for bacterial viability. One of these, Rv0060 (DNA ADP-ribosyl glycohydrolase, DarG_Mtb ), functions along with its cognate toxin Rv0059 (DNA ADP-ribosyl transferase, DarT_Mtb ), to mediate reversible DNA ADP-ribosylation (Jankevicius et al., 2016). We demonstrate that DarT_Mtb -DarG_Mtb form a functional TA pair and essentiality of darG_Mtb is dependent on the presence of darT_Mtb , but simultaneous deletion of both darT_Mtb -darG_Mtb does not alter viability of Mtb in vitro or in mice. The antitoxin, DarG_Mtb , forms a cytosolic complex with DNA-repair proteins that assembles independently of either DarT_Mtb or interaction with DNA. Depletion of DarG_Mtb alone is bactericidal, a phenotype that is rescued by expression of an orthologous antitoxin, DarG_Taq , from Thermus aquaticus. Partial depletion of DarG_Mtb triggers a DNA-damage response and sensitizes Mtb to drugs targeting DNA metabolism and respiration. Induction of the DNA-damage response is essential for Mtb to survive partial DarG_Mtb -depletion and leads to a hypermutable phenotype.

Cross-Regulations between Bacterial Toxin-Antitoxin Systems: Evidence of an Interconnected Regulatory Network?

Toxin-antitoxin (TA) systems are ubiquitous among bacteria and include stable toxins whose toxicity can be counteracted by RNA or protein antitoxins. They are involved in multiple functions that range from stability maintenance for mobile genetic elements to stress adaptation. Bacterial chromosomes frequently have multiple homologues of TA system loci, and it is unclear why there are so many of them. In this review we focus on cross-regulations between TA systems, which occur between both homologous and nonhomologous systems, from similar or distinct types, whether encoded from plasmids or chromosomes. In addition to being able to modulate RNA expression levels, cross-regulations between these systems can also influence their toxicity. This suggests the idea that they are involved in an interconnected regulatory network.

The Variety in the Common Theme of Translation Inhibition by Type II Toxin-Antitoxin Systems

Type II Toxin-antitoxin (TA) modules are bacterial operons that encode a toxic protein and its antidote, which form a self-regulating genetic system. Antitoxins put a halter on toxins in many ways that distinguish different types of TA modules. In type II TA modules, toxin and antitoxin are proteins that form a complex which physically sequesters the toxin, thereby preventing its toxic activity. Type II toxins inhibit various cellular processes, however, the translation process appears to be their favorite target and nearly every step of this complex process is inhibited by type II toxins. The structural features, enzymatic activities and target specificities of the different toxin families are discussed. Finally, this review emphasizes that the structural folds presented by these toxins are not restricted to type II TA toxins or to one particular cellular target, and discusses why so many of them evolved to target translation as well as the recent developments regarding the role(s) of these systems in bacterial physiology and evolution.

PhoH2 proteins couple RNA helicase and RNAse activities

PhoH2 proteins are found in a very diverse range of microorganisms that span bacteria and archaea. These proteins are composed of two domains: an N-terminal PIN-domain fused with a C-terminal PhoH domain. Collectively this fusion functions as an RNA helicase and ribonuclease. In other genomic contexts, PINdomains and PhoHdomains are separate but adjacent suggesting association to achieve similar function. Exclusively among the mycobacteria, PhoH2 proteins are encoded in the genome with an upstream gene, phoAT, which is thought to play the role of an antitoxin (in place of the traditional VapB antitoxin that lies upstream of the 47 other PINdomains in the mycobacterial genome). This review examines PhoH2 proteins as a whole and describes the bioinformatics, biochemical, structural, and biological properties of the two domains that make up PhoH2: PIN and PhoH. We review the transcriptional regulators of phoH2 from two mycobacterial species and speculate on the function of PhoH2 proteins in the context of a Type II toxin-antitoxin system which are thought to play a role in the stress response in bacteria.

Accurate target identification for Mycobacterium tuberculosis endoribonuclease toxins requires expression in their native host

The Mycobacterium tuberculosis genome harbors an unusually high number of toxin-antitoxin (TA) systems. These TA systems have been implicated in establishing the nonreplicating persistent state of this pathogen during latent tuberculosis infection. More than half of the M. tuberculosis TA systems belong to the VapBC (virulence associated protein) family. In this work, we first identified the RNA targets for the M. tuberculosis VapC-mt11 (VapC11, Rv1561) toxin in vitro to learn more about the general function of this family of toxins. Recombinant VapC-mt11 cleaved 15 of the 45 M. tuberculosis tRNAs at a single site within their anticodon stem loop (ASL) to generate tRNA halves. Cleavage was dependent on the presence of a GG consensus sequence immediately before the cut site and a structurally intact ASL. However, in striking contrast to the broad enzyme activity exhibited in vitro, we used a specialized RNA-seq method to demonstrate that tRNA cleavage was highly specific in vivo. Expression of VapC-mt11 in M. tuberculosis resulted in cleavage of only two tRNA isoacceptors containing the GG consensus sequence, tRNA^Gln32-CUG and tRNA^Leu3-CAG. Therefore, our results indicate that although in vitro studies are useful for identification of the class of RNA cleaved and consensus sequences required for accurate substrate recognition by endoribonuclease toxins, definitive RNA target identification requires toxin expression in their native host. The restricted in vivo specificity of VapC-mt11 suggests that it may be enlisted to surgically manipulate pathogen physiology in response to stress.