Ycobacterium Tuberculosis Research Articles

MIP3α-Rel Mtb intranasal DNA vaccination induces reactive T-cell infiltration into the lungs in mice and macaques.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is the leading cause of mortality due to a single infectious organism. While generally curable, TB requires a lengthy and complex antibiotic regimen, due in large part to bacteria that can shift to a persistent state in the presence of antibiotic pressure. Rel Mtb is the primary enzyme regulating the stringent response, which contributes to the metabolic shift of Mtb to a persistent state. Targeting Rel Mtb with a vaccine to eliminate persistent bacteria through the induction of Rel Mtb -specific T-cell immunity in combination with antibiotics to kill dividing bacteria has shown promise in model systems. In a mouse model of Mtb infection, a vaccine created by genetically fusing rel Mtb to the chemokine macrophage inflammatory protein 3α ( MIP3 α), a ligand for the CC chemokine receptor type 6 (CCR6) present on immature dendritic cells, has been shown to enhance T-cell responses and accelerate eradication of infection in mouse models compared to a vaccine lacking the chemokine component. In this study, immunogenicity studies in the mouse and rhesus macaque models provide evidence that intranasal administrations of the DNA form of the MipRel vaccine led to enhanced lung infiltration of T cells after a series of immunizations. Furthermore, despite similar T-cell immunity seen in PBMCs between MipRel and Rel vaccinations, lung and bronchoalveolar lavage cell samples are more enriched for cytokine-secreting T cells in MipRel groups compared to Rel groups. We conclude that intranasal immunization with a MIP-3α fusion vaccine represents a novel strategy for use of a simple DNA vaccine formulation to elicit T-cell immune responses within the respiratory tract. That this formulation is immunogenic in a non-human primate model historically viewed as poorly responsive to DNA vaccines indicates the potential for clinical application in the treatment of Mtb infection, with possible application to other respiratory pathogens. Future studies will further characterize the protective effect of this vaccination platform.

Anti‐synthetase syndrome complicated by multifocal tuberculosis: A thought‐provoking differential diagnosis with tumors

AbstractMycobacterium tuberculosis, which mainly affects the lungs but can also invade other systems, presents a diagnostic challenge when co‐existing with autoimmune disease. We report a case of 31‐year‐old Asian woman with anti‐synthetase syndrome who developed abdominal and subcutaneous lumps during treatment, along with elevated tumor markers, raising suspicion of malignancy. Pathological examination revealed M. tuberculosis infection, changing the diagnosis to multifocal extrapulmonary tuberculosis. This case highlights the need for prompt and detailed evaluations, and the importance of broad differential diagnosis.

Rapid and sensitive diagnosis of live Mycobacterium tuberculosis using clustered regularly interspaced short palindromic repeat‐Cas13a point‐of‐care RNA testing

AbstractMycobacterium tuberculosis (MTB) is the causal pathogen of tuberculosis (TB). Rapid and accurate detection of live MTB is important for transmission control and patient treatment. Here, we described a clustered regularly interspaced short palindromic repeat (CRISPR)‐Cas13a‐based molecular diagnosis approach for rapid and specific detection of live MTB. This detection method, which we termed CRISPR‐Live‐MTB, contained two consecutive reactions including nuclear acid sequence‐based amplification (NASBA) and CRISPR‐Cas13a collateral cleavage reaction. CRISPR‐Live‐MTB could efficiently detect MTB single‐stranded RNA (ssRNA) in 2 hours with high specificity over double‐stranded DNA (dsDNA). Importantly, CRISPR‐Live‐MTB exhibited a limit of detection of 2.4 copies for MTB ssRNA, which was 1000 times lower than that of the clinically used NASBA method. Moreover, lateral flow was integrated into the CRISPR‐Live‐MTB method to enable point‐of‐care testing application with a sensitivity of 95% and a specificity of 100%. Overall, our study demonstrated the feasibility of CRISPR‐Live‐MTB as a rapid, sensitive, and specific approach for live MTB detection.

Propitious Indazole Compounds as β‐ketoacyl‐ACP Synthase Inhibitors and Mechanisms Unfolded for TB Cure: Integrated Rational Design and MD Simulations

AbstractMycobacterium tuberculosis β‐ketoacyl‐ACP synthase I (KasA) involves in mycolic acid biosynthesis for cell wall maintenance; hence, it is a critical target in TB drug design. Thiolactomycin (TLM) and derivatives are the known standard KasA enzyme activity inhibitors. However, TLM analogues have poor activity against KasA protein. Indazole sulphonamide chemotype (JSF‐3285/JFX) was recently reported as a promising KasA enzyme inhibitor. JSF‐3285 mechanism is unclear; thus, it provides a means for designing KasA inhibitors. This study unfolds six hits as unprecedented KasA inhibitors. The inhibitory mechanisms of the screened compounds were investigated and compared with a standard inhibitor (TLM) using integrated molecular informatics and dynamics. JFX, M1, M2, and M5 molecules showed stronger interactions with KasA, having binding energy (kcal/mol) of −44.05, −41.52, −39.51, and −35.9, respectively, against −11.69 for TLM. Molecules showed good predicted inhibitory constants, drug‐likeness, ADME, and synthetic accessibility. KasA complex C‐α atoms RMSD and RMSF showed stable and erratic fluctuations compared to apo KasA. The findings provide potential antimycobacterial lead‐like molecules for future TB drugs.

A Quantitative Method for the Study of HIV-1 and Mycobacterium tuberculosis Coinfection.

Mycobacterium tuberculosis and human immunodeficiency virus-1 (HIV-1) syndemic interactions are a major global health concern. Despite the clinical significance of coinfection, our understanding of the cellular pathophysiology and the therapeutic pharmacodynamic impact of coinfection is limited. Here, we use single-round infectious HIV-1 pseudotyped viral particles expressing green fluorescent protein alongside M. tuberculosis expressing mCherry to study pathogenesis and treatment. We report that HIV-1 infection inhibited intracellular replication of M. tuberculosis and demonstrate the therapeutic activity of antiviral treatment (efavirenz) and antimicrobial treatment (rifampicin). The described method could be applied for detailed mechanistic studies to inform the development of novel treatment strategies.

Preexisting Heterogeneity of Inducible Nitric Oxide Synthase Expression Drives Differential Growth of Mycobacterium tuberculosis in Macrophages.

ABSTRACTMycobacterium tuberculosis infection is initiated by the inhalation and implantation of bacteria in the lung alveoli, where they are phagocytosed by macrophages. Even a single bacterium may be sufficient to initiate infection. Thereafter, the clinical outcome is highly variable between individuals, ranging from sterilization to active disease, for reasons that are not well understood. Here, we show that the rate of intracellular bacterial growth varies markedly between individual macrophages, and this heterogeneity is driven by cell-to-cell variation of inducible nitric oxide synthase (iNOS) activity. At the single-cell level, iNOS expression fluctuates over time, independent of infection or activation with gamma interferon. We conclude that chance encounters between individual bacteria and host cells randomly expressing different levels of an antibacterial gene can determine the outcome of single-cell infections, which may explain why some exposed individuals clear the bacteria while others develop progressive disease.

The β-Grasp Domain of Proteasomal ATPase Mpa Makes Critical Contacts with the Mycobacterium tuberculosis 20S Core Particle to Facilitate Degradation.

ABSTRACTMycobacterium tuberculosis possesses a Pup-proteasome system analogous to the eukaryotic ubiquitin-proteasome pathway. We have previously shown that the hexameric mycobacterial proteasome ATPase (Mpa) recruits pupylated protein substrates via interactions between amino-terminal coiled-coils in Mpa monomers and the degradation tag Pup. However, it is unclear how Mpa rings interact with a proteasome due to the presence of a carboxyl-terminal β-grasp domain unique to Mpa homologues that makes the interaction highly unstable. Here, we describe newly identified critical interactions between Mpa and 20S core proteasomes. Interestingly, the Mpa C-terminal GQYL motif binds the 20S core particle activation pocket differently than the same motif of the ATP-independent proteasome accessory factor PafE. We further found that the β-hairpin of the Mpa β-grasp domain interacts variably with the H0 helix on top of the 20S core particle via a series of ionic and hydrogen-bond interactions. Individually mutating several involved residues reduced Mpa-mediated protein degradation both in vitro and in vivo.IMPORTANCE The Pup-proteasome system in Mycobacterium tuberculosis is critical for this species to cause lethal infections in mice. Investigating the molecular mechanism of how the Mpa ATPase recruits and unfolds pupylated substrates to the 20S proteasomal core particle for degradation will be essential to fully understand how degradation is regulated, and the structural information we report may be useful for the development of new tuberculosis chemotherapies.

M. tuberculosis AlkX Encoded by rv3249c Regulates a Conserved Alkane Hydroxylase System That Is Important for Replication in Macrophages and Biofilm Formation.

ABSTRACTMycobacterium tuberculosis is a highly specialized human pathogen. The success of M. tuberculosis is due to its ability to replicate within host macrophages, resist host immune responses, and ultimately enter a persistent state during a latent tuberculosis infection. Understanding how M. tuberculosis adapts to and replicates in the intracellular environment of the host is crucial for the development of novel, targeted therapeutics. We report the characterization of an M. tuberculosis mutant lacking Rv3249c, a TetR transcriptional regulator. We show that Rv3249c directly represses the adjacent alkB-rubA-rubB operon encoding an alkane hydroxylase/rubredoxin system. For consistency with related systems, we have named the rv3249c gene alkX. The alkX mutant survived better than wild-type M. tuberculosis inside macrophages. This could be phenocopied by overexpression of the alkB-rubA-rubB locus. We hypothesized that the improved intracellular survival phenotype is a result of increased fitness of the mutant; however, we found that the alkX mutant had a defect when grown on some host-associated carbon sources in vitro. We also found that the alkX mutant had a defect in biofilm formation, also linked to the overexpression of the alkB-rubAB genes. Combined, these results define the primary role of AlkX as a transcriptional repressor of the alkB-rubAB operon and suggest the operon contributes to intracellular survival of the pathogen.IMPORTANCE Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is the leading cause of death worldwide due to a single infectious agent. It is important to understand how M. tuberculosis adapts to and replicates in the intracellular environment of the host. In this study, we characterized the TetR transcriptional regulator Rv3249c and show that it regulates a highly conserved alkane hydroxylase/rubredoxin system. Our data demonstrate that the AlkBRubAB system contributes to the success of the bacterium in host macrophages.

Visualizing Pyrazinamide Action by Live Single-Cell Imaging of Phagosome Acidification and Mycobacterium tuberculosis pH Homeostasis.

ABSTRACTMycobacterium tuberculosis segregates within multiple subcellular niches with different biochemical and biophysical properties that, upon treatment, may impact antibiotic distribution, accumulation, and efficacy. However, it remains unclear whether fluctuating intracellular microenvironments alter mycobacterial homeostasis and contribute to antibiotic enrichment and efficacy. Here, we describe a live dual-imaging approach to monitor host subcellular acidification and M. tuberculosis intrabacterial pH. By combining this approach with pharmacological and genetic perturbations, we show that M. tuberculosis can maintain its intracellular pH independently of the surrounding pH in human macrophages. Importantly, unlike bedaquiline (BDQ), isoniazid (INH), or rifampicin (RIF), the drug pyrazinamide (PZA) displays antibacterial efficacy by disrupting M. tuberculosis intrabacterial pH homeostasis in cellulo. By using M. tuberculosis mutants, we confirmed that intracellular acidification is a prerequisite for PZA efficacy in cellulo. We anticipate this imaging approach will be useful to identify host cellular environments that affect antibiotic efficacy against intracellular pathogens.

Machine Learning of All Mycobacterium tuberculosis H37Rv RNA-seq Data Reveals a Structured Interplay between Metabolism, Stress Response, and Infection.

ABSTRACTMycobacterium tuberculosis is one of the most consequential human bacterial pathogens, posing a serious challenge to 21st century medicine. A key feature of its pathogenicity is its ability to adapt its transcriptional response to environmental stresses through its transcriptional regulatory network (TRN). While many studies have sought to characterize specific portions of the M. tuberculosis TRN, and some studies have performed system-level analysis, few have been able to provide a network-based model of the TRN that also provides the relative shifts in transcriptional regulator activity triggered by changing environments. Here, we compiled a compendium of nearly 650 publicly available, high quality M. tuberculosis RNA-sequencing data sets and applied an unsupervised machine learning method to obtain a quantitative, top-down TRN. It consists of 80 independently modulated gene sets known as “iModulons,” 41 of which correspond to known regulons. These iModulons explain 61% of the variance in the organism’s transcriptional response. We show that iModulons (i) reveal the function of poorly characterized regulons, (ii) describe the transcriptional shifts that occur during environmental changes such as shifting carbon sources, oxidative stress, and infection events, and (iii) identify intrinsic clusters of regulons that link several important metabolic systems, including lipid, cholesterol, and sulfur metabolism. This transcriptome-wide analysis of the M. tuberculosis TRN informs future research on effective ways to study and manipulate its transcriptional regulation and presents a knowledge-enhanced database of all published high-quality RNA-seq data for this organism to date.IMPORTANCE Mycobacterium tuberculosis H37Rv is one of the world's most impactful pathogens, and a large part of the success of the organism relies on the differential expression of its genes to adapt to its environment. The expression of the organism's genes is driven primarily by its transcriptional regulatory network, and most research on the TRN focuses on identifying and quantifying clusters of coregulated genes known as regulons. While previous studies have relied on molecular measurements, in the manuscript we utilized an alternative technique that performs machine learning to a large data set of transcriptomic data. This approach is less reliant on hypotheses about the role of specific regulatory systems and allows for the discovery of new biological findings for already collected data. A better understanding of the structure of the M. tuberculosis TRN will have important implications in the design of improved therapeutic approaches.

Deterministic and stochastic in-host tuberculosis models for bacterium-directed and host-directed therapy combination.

Mycobacterium tuberculosis (TB) infection can involve all immune system components and can result in different disease outcomes. The antibiotic TB drugs require strict adherence to prevent both disease relapse and mutation of drug- and multidrug-resistant strains. To overcome the constraints of pathogen-directed therapy, host-directed therapy has attracted more attention in recent years as an adjunct therapy to enhance host immunity to fight against this intractable pathogen. The goal of this paper is to investigate in-host TB models to provide insights into therapy development. Focusing on therapy-targeting parameters, the parameter regions for different disease outcomes are identified from an established ODE model. Interestingly, the ODE model also demonstrates that the immune responses can both benefit and impede disease progression, depending on the number of bacteria engulfed and released by macrophages. We then develop two Itô SDE models, which consider the impact of demographic variations at the cellular level and environmental variations during therapies along with demographic variations. The SDE model with demographic variation suggests that stochastic fluctuations at the cellular level have significant influences on (1) the T-cell population in all parameter regions, (2) the bacterial population when parameters located in the region with multiple disease outcomes and (3) the uninfected macrophage population in the parameter region representing active disease. Further, considering environmental variations from therapies, the second SDE model suggests that disease progression can slow down if therapies (1) can have fast return rates and (2) can bring parameter values into the disease clearance regions.

Donor-derived tuberculosis among solid organ transplant recipients in the United States-2008 to 2018.

Mycobacterium tuberculosis can be transmitted via organ donation and result in severe outcomes. To better understand donor-derived tuberculosis (DDTB), all potential transmissions reported to the Organ Procurement and Transplantation Network (OPTN) Ad Hoc Disease Transmission Advisory Committee between 2008 and 2018 were analyzed. Among 51 total reports, nine (17%) (9 donors/35 recipients) had≥1 recipient with proven/probable disease transmission. Of these, eight were reported due to recipient disease, and one was reported due to a positive donor result. Proven/probable DDTB transmissions were reported in six lung and five nonlung recipients. The median time to diagnosis was 104 days posttransplant (range 0-165 days). Pulmonary TB, extrapulmonary TB, pulmonary plus extrapulmonary TB, and asymptomatic TB infection with positive interferon-gamma release assay were present in five, three, one, and two recipients, respectively. All recipients received treatment and survived except for one whose death was not attributed to TB. All donors associated with proven/probable DDTB had≥1TB risk factor. Six were born in a TB-endemic country, five had traveled to a TB-endemic country, three had been incarcerated, and three had latent TB infection. These cases highlight the importance of evaluating donors for TB based on risk factors. Early posttransplant TB in organ recipients of donors with TB risk factors requires prompt reporting to OPTN to identify other potential affected recipients and implement timely treatment interventions.

Characterization of a triazole scaffold compound as an inhibitor of Mycobacterium tuberculosis imidazoleglycerol-phosphate dehydratase.

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis (TB), employs ten enzymes including imidazoleglycerol-phosphate dehydratase (IGPD) for de novo biosynthesis of histidine. The absence of histidine-biosynthesis in humans combined with its essentiality for Mtb makes the enzymes of this pathway major anti-TB drug targets. We explored the inhibitory potential of a small molecule β-(1,2,4-Triazole-3-yl)-DL-alanine (DLA) against Mtb IGPD. DLA exhibits an in vitro inhibitory efficacy in the lower micromolar range. Higher-resolution crystal structures of native and substrate-bound Mtb IGPD provided additional structural features of this important drug target. Crystal structure of IGPD-DLA complex at a resolution of 1.75 Å, confirmed that DLA locks down the function of the enzyme by binding in the active site pocket of the IGPD mimicking the substrate-binding mode to a high degree. In our biochemical study, DLA showed an efficient inhibition of Mtb IGPD. Furthermore, DLA also showed bactericidal activity against Mtb and Mycobacterium smegmatis and inhibited their growth in respective culture medium. Importantly, owing to the favorable ADME and physicochemical properties, it serves as an important lead molecule for further derivatizations.

Galectin-8 Senses Phagosomal Damage and Recruits Selective Autophagy Adapter TAX1BP1 To Control Mycobacterium tuberculosis Infection in Macrophages.

ABSTRACTMycobacterium tuberculosis (Mtb) causes one of the deadliest infectious diseases worldwide. Upon infection, Mtb is phagocytosed by macrophages and uses its virulence-associated ESX-1 secretion system to modulate the host cell. We showed previously that the ESX-1 secretion system perturbs the Mtb-containing phagosome, and a population (∼30%) of intracellular Mtb is tagged with ubiquitin and targeted to selective autophagy. However, our understanding of how macrophages sense and respond to damaged Mtb-containing phagosomes remains incomplete. Here, we demonstrate that several cytosolic glycan-binding proteins called galectins recognize Mtb-containing phagosomes; in macrophage cell lines and in primary macrophages, galectin-3, -8, and -9 are all recruited to the same Mtb population that colocalizes with selective autophagy markers (ubiquitin, p62, and LC3). To test whether galectins are required for controlling Mtb replication in macrophages, we generated CRISPR/Cas9 knockouts and found that galectin-8−/− and galectin-3/8/9−/− macrophages were similarly defective in targeting Mtb to selective autophagy and controlling replication. This suggests galectin-8 plays a unique role in anti-Mtb autophagy. In investigating galectin-8's role, we identified a novel and specific interaction between galectin-8 and the selective autophagy adapter TAX1BP1 and found that this galectin-8/TAX1BP1 interaction was necessary for macrophages to efficiently target Mtb to selective autophagy. Remarkably, overexpressing galectin-8 increased targeting of Mtb to autophagy and limited Mtb replication. Taken together, these data demonstrate that while several galectins are capable of recognizing damaged Mtb-containing phagosomes, galectin-8 plays a privileged role in recruiting downstream autophagy machinery and may represent a promising target for host-directed tuberculosis therapies.

TB or not TB? Definitive determination of species within the Mycobacterium tuberculosis complex in unprocessed sputum from adults with presumed multidrug-resistant tuberculosis.

ObjectivesDifferences among Mycobacterium tuberculosis complex (MTC) species may predict drug resistance or treatment success. Thus, we optimised and deployed the genotype MTBC assay (gMTBC) to identify MTC to the species level, and then performed comparative genotypic drug‐susceptibility testing to anti‐tuberculosis drugs from direct sputum of patients with presumed multidrug‐resistant tuberculosis (MDR‐TB) by the MTBDRplus/sl reference method.MethodsPatients with positive Xpert® MTB/RIF (Xpert) results were consented to provide early‐morning‐sputum for testing by the gMTBC and the reference MTBDRplus/sl. Chi‐square or Fisher’s exact test compared proportions. Modified Poisson regression modelled detection of MTC by gMTBC.ResultsAmong 73 patients, 53 (73%) were male and had a mean age of 43 (95% CI; 40–45) years. In total, 34 (47%), 36 (49%) and 38 (55%) had positive gMTBC, culture and MTBDR respectively. Forty patients (55%) had low quantity MTC by Xpert, including 31 (78%) with a negative culture. gMTBC was more likely to be positive in patients with chest cavity 4.18 (1.31–13.32, P = 0.016), high‐quantity MTC by Xpert 3.03 (1.35–6.82, P = 0.007) and sputum smear positivity 1.93 (1.19–3.14, P = 0.008). The accuracy of gMTBC in detecting MTC was 95% (95% CI; 86–98; κ = 0.89) compared to MTBDRplus/sl. All M. tuberculosis/canettii identified by gMTB were susceptible to fluoroquinolone and aminoglycosides/capreomycin.ConclusionsThe concordance between the gMTBC assay and MTBDRplus/sl in detecting MTC was high but lagged behind the yield of Xpert MTB/RIF. All M. tuberculosis/canettii were susceptible to fluoroquinolones, a core drug in MDR‐TB treatment regimens.

Macrophage Infection Models for Mycobacterium tuberculosis.

Mycobacterium tuberculosis colonizes, survives, and grows inside macrophages. In vitro macrophage infection models, using both primary macrophages and cell lines, enable the characterization of the pathogen response to macrophage immune pressure and intracellular environmental cues. We describe methods to propagate and infect primary murine bone marrow-derived macrophages, HoxB8 conditionally immortalized myeloid cells, Max Planck Institute alveolar macrophage-like cells, and J774 and THP-1 macrophage-like cell lines. We also present methods on the characterization of M. tuberculosis intracellular survival and the preparation of infected macrophages for imaging.

PositiveMycobacterium tuberculosisGastric Lavage Cultures from Asymptomatic Children With Normal Chest Radiography

Mycobacterium tuberculosis culture from gastric lavage from apparently healthy children following tuberculin skin test conversion, despite normal chest radiography (CR), is well known but is a contentious subject. A consensus statement regarding classification of childhood tuberculosis excluded this condition, stating that more data were needed. To assist in this discussion, we reviewed early publications that reported the occurrence of this phenomenon and early anatomical pathology studies that described changes that occur in children following tuberculosis infection. Pathology studies describe frequent cavitation in primary foci in children from whom positive M. tuberculosis cultures might easily arise. These foci were very small in some children who might have normal CR. Positive cultures might also arise from ulcerated mediastinal lymph nodes that are invisible on CR. Young children with recent infection very likely have active primary pulmonary tuberculosis.

In silico study directed towards identification of the key structural features of GyrB inhibitors targeting MTB DNA gyrase: HQSAR, CoMSIA and molecular dynamics simulations

ABSTRACTMycobacterium tuberculosis DNA gyrase subunit B (GyrB) has been identified as a promising target for rational drug design against fluoroquinolone drug-resistant tuberculosis. In this study, we attempted to identify the key structural feature for highly potent GyrB inhibitors through 2D-QSAR using HQSAR, 3D-QSAR using CoMSIA and molecular dynamics (MD) simulations approaches on a series of thiazole urea core derivatives. The best HQSAR and CoMSIA models based on IC50 and MIC displayed the structural basis required for good activity against both GyrB enzyme and mycobacterial cell. MD simulations and binding free energy analysis using MM-GBSA and waterswap calculations revealed that the urea core of inhibitors has the strongest interaction with Asp79 via hydrogen bond interactions. In addition, cation-pi interaction and hydrophobic interactions of the R2 substituent with Arg82 and Arg141 help to enhance the binding affinity in the GyrB ATPase binding site. Thus, the present study provides crucial structural features and a structural concept for rational design of novel DNA gyrase inhibitors with improved biological activities against both enzyme and mycobacterial cell, and with good pharmacokinetic properties and drug safety profiles.

Equal opportunity nitrogen sourcing

Pathogen Metabolism M ycobacterium tuberculosis (Mtb) has an unusual growth profile and metabolism, requiring around 20 hours to double in rich culture medium. A better understanding of Mtb metabolic requirements, particularly fundamental transformations such as nitrogen assimilation, may reveal weaknesses that can be exploited in drug design or other therapies. Agapova et al. cultured Mtb with each of the 20 proteinogenic amino acids, looking for differences in how nitrogen was incorporated into metabolites in the growing cells. Intracellular pools of amino acids varied in every case, suggesting a complex and flexible metabolism in which nitrogen is ideally obtained from amino acids rather than free ammonium. The enzyme alanine dehydrogenase exclusively liberated ammonium from alanine, suggesting a possible role for this enzyme and amino acid in nitrogen storage in Mtb. eLife 8 , e41129 (2019).

Inhibition of Mycobacterium tuberculosis L,D‐Transpeptidase 5 by Carbapenems: MD and QM/MM Mechanistic Studies

AbstractMycobacterium tuberculosis (Mtb) is the bacteria that currently claims the most number of human lives each year. The final step of peptidoglycan synthesis involves the generation of 4→3 and 3→3 transpeptide crosslinks catalyzed by D,D‐transpeptidase and L,D‐transpeptidase (Ldt) enzymes, respectively. Unlike in most other bacteria, for Mtb, the majority of the cross‐links are generated by L,D‐transpeptidases. LdtMt5 knock‐out strains of Mtb displayed aberrant growth, and are susceptibility to crystal violet, osmotic shock, and selected carbapenem antibiotics. Here, we used molecular dynamics (MD) and Quantum Mechanical (QM) simulations to probe the molecular interactions of LdtMt5 with carbapenems. LdtMt5 complexes with three carbapenems, ertapenem (ERT), imipenem (IMI) and meropenem (MERO) were simulated. The binding free energies of these complexes were calculated from the MD trajectories using the MM/GBSA approach, the theoretical results revealed higher ▵Gbind for ERT—LdtMt5 and IMI—LdtMt5 than MERO—LdtMt5. To further understand the catalytic reaction mechanism of LdtMt5 with the selected carbapenems, the possible reaction pathway was investigated. The high free energies of activation (▵G) for imipenem and meropenem, explain the reason behind inefficient binding of these carbapenems to LdtMt5. These results provide a better understanding of how the antibacterial agents function and will potentially contribute to the discovery of more potent LdtMt5 inhibitors.