MabA (FabG1), a Mycobacterium tuberculosis protein involved in the long-chain fatty acid elongation system FAS-II

In Silico Approach: Anti-Tuberculosis Activity of Caespitate in the H37Rv Strain

Tuberculosis is a highly lethal bacterial disease worldwide caused by Mycobacterium tuberculosis (Mtb). Caespitate is a phytochemical isolated from Helichrysum caespititium, a plant used in African traditional medicine that shows anti-tubercular activity, but its mode of action remains unknown. It is suggested that there are four potential targets in Mtb, specifically in the H37Rv strain: InhA, MabA, and UGM, enzymes involved in the formation of Mtb's cell wall, and PanK, which plays a role in cell growth. Two caespitate conformational structures from DFT conformational analysis in the gas phase (GC) and in solution with DMSO (CS) were selected. Molecular docking calculations, MM/GBSA analysis, and ADME parameter evaluations were performed. The docking results suggest that CS is the preferred caespitate conformation when interacting with PanK and UGM. In both cases, the two intramolecular hydrogen bonds characteristic of caespitate's molecular structure were maintained to achieve the most stable complexes. The MM/GBSA study confirmed that PanK/caespitate and UGM/caespitate were the most stable complexes. Caespitate showed favorable pharmacokinetic characteristics, suggesting rapid absorption, permeability, and high bioavailability. Additionally, it is proposed that caespitate may exhibit antibacterial and antimonial activity. This research lays the foundation for the design of anti-tuberculosis drugs from natural sources, especially by identifying potential drug targets in Mtb.

Structural and functional characterization of FabG4 from Mycolicibacterium smegmatis

The rise in antimicrobial resistance is a global health crisis and necessitates the development of novel strategies to treat infections. For example, in 2022 tuberculosis (TB) was the second leading infectious killer after COVID-19, with multi-drug-resistant strains of TB having an ∼40% fatality rate. Targeting essential biosynthetic pathways in pathogens has proven to be successful for the development of novel antimicrobial treatments. Fatty-acid synthesis (FAS) in bacteria proceeds via the type II pathway, which is substantially different from the type I pathway utilized in animals. This makes bacterial fatty-acid biosynthesis (Fab) enzymes appealing as drug targets. FabG is an essential FASII enzyme, and some bacteria, such as Mycobacterium tuberculosis, the causative agent of TB, harbor multiple homologs. FabG4 is a conserved, high-molecular-weight FabG (HMwFabG) that was first identified in M. tuberculosis and is distinct from the canonical low-molecular-weight FabG. Here, structural and functional analyses of Mycolicibacterium smegmatis FabG4, the third HMwFabG studied to date, are reported. Crystal structures of NAD+ and apo MsFabG4, along with kinetic analyses, show that MsFabG4 preferentially binds and uses NADH when reducing CoA substrates. As M. smegmatis is often used as a model organism for M. tuberculosis, these studies may aid the development of drugs to treat TB and add to the growing body of research that distinguish HMwFabGs from the archetypal low-molecular-weight FabG.

Identification of potential inhibitor molecule against MabA protein of Mycobacterium leprae by integrated in silico approach

Leprosy is one of the chronic diseases with which humanity has struggled globally for millennia. The potent anti-leprosy medications rifampicin, clofazimine and dapsone, among others, are used to treat leprosy. Nevertheless, even in regions of the world where these drugs have been successfully implemented, resistance continues to be observed. Due to the problems with the current treatments, this disease should be fought at every level of society with new drugs. The purpose of this research was to identify natural candidates with the ability to inhibit MabA (gene-fabG1) with fewer negative effects. The work was accomplished through molecular docking, followed by a dynamic investigation of protein-ligand, which play a significant role in the design of pharmaceuticals. After modelling the protein structure with MODELLER 9.21v, AutoDock Vina was used to perform molecular docking with 13 3 D anti-leprosy medicines and a zinc library to determine the optimal protein-ligand interaction. In addition, the docking result was filtered based on binding energy, ADMET characteristics, PASS analysis and the most crucial binding residues. The ZINC08101051 chemical compound was prioritized for further study. Using an all-atom 100 ns MD simulation, the binding pattern and conformational changes in protein upon ligand binding were studied. Recommendation for subsequent validation based on deviation, fluctuation, gyration and hydrogen bond analysis, followed by main component and free energy landscape.Communicated by Ramaswamy H. Sarma.

New therapeutic strategies for Mycobacterium abscessus pulmonary diseases - untapping the mycolic acid pathway

INTRODUCTION

Treatment options against Mycobacterium abscessus infections are very limited. New compounds are needed to cure M. abscessus pulmonary diseases. While the mycolic acid biosynthetic pathway has been largely exploited for the treatment of tuberculosis, this metabolic process has been overlooked in M. abscessus, although it offers many potential drug targets for the treatment of this opportunistic pathogen.

AREAS COVERED

Herein, the authors review the role of the MmpL3 membrane protein and the enoyl-ACP reductase InhA involved in the transport and synthesis of mycolic acids, respectively. They discuss their importance as two major vulnerable drug targets in M. abscessus and report the activity of MmpL3 and InhA inhibitors. In particular, they focus on NITD-916, a direct InhA inhibitor against M. abscessus, particularly warranted in the context of multidrug resistance.

EXPERT OPINION

There is an increasing body of evidence validating the mycolic acid pathway as an attractive drug target to be further exploited for M. abscessus lung disease treatments. The NITD-916 studies provide a proof-of-concept that direct inhibitors of InhA are efficient in vitro, in macrophages and in zebrafish. Future work is now required to improve the activity and pharmacological properties of these inhibitors and their evaluation in pre-clinical models.

Insights into the central role of N-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU) in peptidoglycan metabolism and its potential as a therapeutic target

Several decades after the discovery of the first antibiotic (penicillin) microbes have evolved novel mechanisms of resistance; endangering not only our abilities to combat future bacterial pandemics but many other clinical challenges such as acquired infections during surgeries. Antimicrobial resistance (AMR) is attributed to the mismanagement and overuse of these medications and is complicated by a slower rate of the discovery of novel drugs and targets. Bacterial peptidoglycan (PG), a three-dimensional mesh of glycan units, is the foundation of the cell wall that protects bacteria against environmental insults. A significant percentage of drugs target PG, however, these have been rendered ineffective due to growing drug resistance. Identifying novel druggable targets is, therefore, imperative. Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) is one of the key building blocks in PG production, biosynthesized by the bifunctional enzyme N-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU). UDP-GlcNAc metabolism has been studied in many organisms, but it holds some distinctive features in bacteria, especially regarding the bacterial GlmU enzyme. In this review, we provide an overview of different steps in PG biogenesis, discuss the biochemistry of GlmU, and summarize the characteristic structural elements of bacterial GlmU vital to its catalytic function. Finally, we will discuss various studies on the development of GlmU inhibitors and their significance in aiding future drug discoveries.

Recent advances in Fragment-based strategies against tuberculosis

Tuberculosis remains one of the world's leading infectious disease killers, causing more than 1.5 million of deaths each year. It is therefore a priority to discover and develop new classes of anti-tuberculosis drugs to design new treatments in order to fight the increasing burden of resistant-tuberculosis. Fragment-based drug discovery (FBDD) relies on the identification of small molecule hits, further improved to high-affinity ligands through three main approaches: fragment growing, merging and linking. The aim of this review is to highlight the recent progresses made in fragment-based approaches for the discovery and development of Mycobacterium tuberculosis inhibitors in a wide range of pathways. Hit discovery, hit-to-lead optimization, SAR and binding mode when available are discussed.

Crystal structure of a putative 3-hydroxypimelyl-CoA dehydrogenase, Hcd1, from Syntrophus aciditrophicus strain SB at 1.78 Å resolution

Syntrophus aciditrophicus strain SB is a model syntroph that degrades benzoate and alicyclic acids. The structure of a putative 3-hydroxypimelyl-CoA dehydrogenase from S. aciditrophicus strain SB (SaHcd1) was resolved at 1.78 Å resolution. SaHcd1 contains sequence motifs and structural features that belong to the short-chain dehydrogenase/reductase (SDR) family of NADPH-dependent oxidoreductases. SaHcd1 is proposed to concomitantly reduce NAD+ or NADP+ to NADH or NADPH, respectively, while converting 3-hydroxypimelyl-CoA to 3-oxopimeyl-CoA. Further enzymatic studies are needed to confirm the function of SaHcd1.

Exploring the Antitubercular Activity of Anthranilic Acid Derivatives: From MabA (FabG1) Inhibition to Intrabacterial Acidification

Mycobacterium tuberculosis, the pathogen that causes tuberculosis, is responsible for the death of 1.5 million people each year and the number of bacteria resistant to the standard regimen is constantly increasing. This highlights the need to discover molecules that act on new M. tuberculosis targets. Mycolic acids, which are very long-chain fatty acids essential for M. tuberculosis viability, are synthesized by two types of fatty acid synthase (FAS) systems. MabA (FabG1) is an essential enzyme belonging to the FAS-II cycle. We have recently reported the discovery of anthranilic acids as MabA inhibitors. Here, the structure–activity relationships around the anthranilic acid core, the binding of a fluorinated analog to MabA by NMR experiments, the physico-chemical properties and the antimycobacterial activity of these inhibitors were explored. Further investigation of the mechanism of action in bacterio showed that these compounds affect other targets than MabA in mycobacterial cells and that their antituberculous activity is due to the carboxylic acid moiety which induces intrabacterial acidification.

Molecular Mechanisms of MmpL3 Function and Inhibition

Mycobacteria species include a large number of pathogenic organisms such as Mycobacterium tuberculosis, Mycobacterium leprae, and various non-tuberculous mycobacteria. Mycobacterial membrane protein large 3 (MmpL3) is an essential mycolic acid and lipid transporter required for growth and cell viability. In the last decade, numerous studies have characterized MmpL3 with respect to protein function, localization, regulation, and substrate/inhibitor interactions. This review summarizes new findings in the field and seeks to assess future areas of research in our rapidly expanding understanding of MmpL3 as a drug target. An atlas of known MmpL3 mutations that provide resistance to inhibitors is presented, which maps amino acid substitutions to specific structural domains of MmpL3. In addition, chemical features of distinct classes of Mmpl3 inhibitors are compared to provide insights into shared and unique features of varied MmpL3 inhibitors.

The pathogenic mechanism of Mycobacterium tuberculosis: implication for new drug development

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a tenacious pathogen that has latently infected one third of the world's population. However, conventional TB treatment regimens are no longer sufficient to tackle the growing threat of drug resistance, stimulating the development of innovative anti-tuberculosis agents, with special emphasis on new protein targets. The Mtb genome encodes ~4000 predicted proteins, among which many enzymes participate in various cellular metabolisms. For example, more than 200 proteins are involved in fatty acid biosynthesis, which assists in the construction of the cell envelope, and is closely related to the pathogenesis and resistance of mycobacteria. Here we review several essential enzymes responsible for fatty acid and nucleotide biosynthesis, cellular metabolism of lipids or amino acids, energy utilization, and metal uptake. These include InhA, MmpL3, MmaA4, PcaA, CmaA1, CmaA2, isocitrate lyases (ICLs), pantothenate synthase (PS), Lysine-ε amino transferase (LAT), LeuD, IdeR, KatG, Rv1098c, and PyrG. In addition, we summarize the role of the transcriptional regulator PhoP which may regulate the expression of more than 110 genes, and the essential biosynthesis enzyme glutamine synthetase (GlnA1). All these enzymes are either validated drug targets or promising target candidates, with drugs targeting ICLs and LAT expected to solve the problem of persistent TB infection. To better understand how anti-tuberculosis drugs act on these proteins, their structures and the structure-based drug/inhibitor designs are discussed. Overall, this investigation should provide guidance and support for current and future pharmaceutical development efforts against mycobacterial pathogenesis.

The Role of Phosphorylation and Acylation in the Regulation of Drug Resistance in Mycobacterium tuberculosis

Tuberculosis is a chronic and lethal infectious disease caused by Mycobacterium tuberculosis. In previous decades, most studies in this area focused on the pathogenesis and drug targets for disease treatments. However, the emergence of drug-resistant strains has increased the difficulty of clinical trials over time. Now, more post-translational modified proteins in Mycobacterium tuberculosis have been discovered. Evidence suggests that these proteins have the ability to influence tuberculosis drug resistance. Hence, this paper systematically summarizes updated research on the impacts of protein acylation and phosphorylation on the acquisition of drug resistance in Mycobacterium tuberculosis through acylation and phosphorylation protein regulating processes. This provides us with a better understanding of the mechanism of antituberculosis drugs and may contribute to a reduction the harm that tuberculosis brings to society, as well as aiding in the discovery of new drug targets and therapeutic regimen adjustments in the future.

A Novel Acyl-AcpM-Binding Protein Confers Intrinsic Sensitivity to Fatty Acid Synthase Type II Inhibitors in Mycobacterium smegmatis

The fatty acid synthase type II (FAS-II) multienzyme system is the main target of drugs to inhibit mycolic acid synthesis in mycobacterium. Meromycolate extension acyl carrier protein (AcpM) serves as the carrier of fatty acyl chain shuttling among the individual FAS-II components during the progression of fatty acid elongation. In this paper, MSMEG_5634 in Mycobacterium smegmatis was determined to be a helix-grip structure protein with a deep hydrophobic pocket, preferring to form a complex with acyl-AcpM containing a fatty acyl chain at the C36-52 length, which is the medium product of FAS-II. MSMEG_5634 interacted with FAS-II components and presented relative accumulation at the cellular pole. By forming the MSMEG_5634/acyl-AcpM complex, which is free from FAS-II, MSMEG_5634 could transport acyl-AcpM away from FAS-II. Deletion of the MSMEG_5634 gene in M. smegmatis resulted in a mutant with decreased sensitivity to isoniazid and triclosan, two inhibitors of the FAS-II system. The isoniazid and triclosan sensitivity of this mutant could be restored by the ectopic expression of MSMEG_5634 or Rv0910, the MSMEG_5634 homologous protein in Mycobacterium tuberculosis H37Rv. These results suggest that MSMEG_5634 and its homologous proteins, forming a novel acyl-AcpM-binding protein family in mycobacterium, confer intrinsic sensitivity to FAS-II inhibitors.

The thick waxy coat of mycobacteria, a protective layer against antibiotics and the host's immune system

Tuberculosis, caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb), is the leading cause of death from an infectious disease, with a mortality rate of over a million people per year. This pathogen's remarkable resilience and infectivity is largely due to its unique waxy cell envelope, 40% of which comprises complex lipids. Therefore, an understanding of the structure and function of the cell wall lipids is of huge indirect clinical significance. This review provides a synopsis of the cell envelope and the major lipids contained within, including structure, biosynthesis and roles in pathogenesis.

Antibiotics and resistance: the two-sided coin of the mycobacterial cell wall

Mycobacterium tuberculosis, the bacterium responsible for tuberculosis, is the global leading cause of mortality from an infectious agent. Part of this success relies on the unique cell wall, which consists of a thick waxy coat with tightly packed layers of complexed sugars, lipids and peptides. This coat provides a protective hydrophobic barrier to antibiotics and the host's defences, while enabling the bacterium to spread efficiently through sputum to infect and survive within the macrophages of new hosts. However, part of this success comes at a cost, with many of the current first- and second-line drugs targeting the enzymes involved in cell wall biosynthesis. The flip side of this coin is that resistance to these drugs develops either in the target enzymes or the activation pathways of the drugs, paving the way for new resistant clinical strains. This review provides a synopsis of the structure and synthesis of the cell wall and the major current drugs and targets, along with any mechanisms of resistance.

The Analysis of Estrogen-Degrading and Functional Metabolism Genes in Rhodococcus equi DSSKP-R-001

Estrogen contamination is recognized as one of the most serious environmental problems, causing widespread concern worldwide. Environmental estrogens are mainly derived from human and vertebrate excretion, drugs, and agricultural activities. The use of microorganisms is currently the most economical and effective method for biodegradation of environmental estrogens. Rhodococcus equi DSSKP-R-001 (R-001) has strong estrogen-degrading capabilities. Our study indicated that R-001 can use different types of estrogen as its sole carbon source for growth and metabolism, with final degradation rates above 90%. Transcriptome analysis showed that 720 (E1), 983 (E2), and 845 (EE2) genes were significantly upregulated in the estrogen-treated group compared with the control group, and 270 differentially expressed genes (DEGs) were upregulated across all treatment groups. These DEGs included ABC transporters; estrogen-degrading genes, including those that perform initial oxidation and dehydrogenation reactions and those that further degrade the resulting substrates into small molecules; and metabolism genes that complete the intracellular transformation and utilization of estrogen metabolites through biological processes such as amino acid metabolism, lipid metabolism, carbohydrate metabolism, and the tricarboxylic acid cycle. In summary, the biodegradation of estrogens is coordinated by a metabolic network of estrogen-degrading enzymes, transporters, metabolic enzymes, and other coenzymes. In this study, the metabolic mechanisms by which Rhodococcus equi R-001 degrades various estrogens were analyzed for the first time. A new pollutant metabolism system is outlined, providing a starting point for the construction of engineered estrogen-degrading bacteria.

Identification and validation of the mode of action of the chalcone anti-mycobacterial compounds

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Chalcone 1a inhibits the growth of Mycobacterium bovis BCG (MIC 6.25 µg.ml⁻¹).

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Chalcone 1a directly targets InhA.

Objectives

The search for new TB drugs has become one of the great challenges for modern medicinal chemistry. An improvement in the outcomes of TB chemotherapy can be achieved by the development of new, shorter, cheap, safe and effective anti-TB regimens.

Methods

Chalcones (1a-1o) were synthesized and evaluated for their antimycobacterial activity against Mycobacterium bovis BCG using growth inhibition assays. Compound 1a was selected as a ‘hit’ compound. The mode of action of compound 1a, was identified by mycolic acid methyl esters (MAMEs) and fatty acid methyl esters (FAMEs) analysis using thin layer chromatography. Dose dependent experiments were conducted by over-expressing components of FAS-II in M. bovis BCG to confirm the target. Ligand binding using intrinsic tryptophan assay and molecular docking were used to further validate the target.

Results

MAMEs and FAMEs analysis showed dose-dependent reduction of MAMEs with the overall abundance of FAMEs suggesting that compound 1a targets mycolic acid biosynthesis. Direct binding of 1a to InhA was observed using an intrinsic tryptophan fluorescence binding assay, and a 2-fold IC₅₀ shift was observed with an InhA overexpressing strain confirming InhA as the cellular target.

Conclusion

The chalcone 1a exhibits potent antimycobacterial activity, displays a good safety profile and is a direct inhibitor of InhA, a key component in mycolic acid synthesis, validating this series for further anti-TB drug development.

New tuberculosis drug targets, their inhibitors, and potential therapeutic impact

The current tuberculosis (TB) predicament poses numerous challenges and therefore every incremental scientific work and all positive socio-political engagements, are steps taken in the right direction to eradicate TB. Progression of the late stage TB-drug pipeline into the clinics is an immediate deliverable of this global effort. At the same time, fueling basic research and pursuing early discovery work must be sustained to maintain a healthy TB-drug pipeline. This review encompasses a broad analysis of chemotherapeutic strategies that target the DNA replication, protein synthesis, cell wall biosynthesis, energy metabolism and proteolysis of Mycobacterium tuberculosis (Mtb). It includes a status check of the current TB-drug pipeline with a focus on the associated biology, emerging targets, and their promising chemical inhibitors. Potential synergies and/or gaps within or across different chemotherapeutic strategies are systematically reviewed as well.

Discovery of the first Mycobacterium tuberculosis MabA (FabG1) inhibitors through a fragment-based screening

Mycobacterium tuberculosis (M.tb), the etiologic agent of tuberculosis, remains the leading cause of death from a single infectious agent worldwide. The emergence of drug-resistant M.tb strains stresses the need for drugs acting on new targets. Mycolic acids are very long chain fatty acids playing an essential role in the architecture and permeability of the mycobacterial cell wall. Their biosynthesis involves two fatty acid synthase (FAS) systems. Among the four enzymes (MabA, HadAB/BC, InhA and KasA/B) of the FAS-II cycle, MabA (FabG1) remains the only one for which specific inhibitors have not been reported yet. The development of a new LC-MS/MS based enzymatic assay allowed the screening of a 1280 fragment-library and led to the discovery of the first small molecules that inhibit MabA activity. A fragment from the anthranilic acid series was optimized into more potent inhibitors and their binding to MabA was confirmed by ¹⁹F ligand-observed NMR experiments.

Discovery of a novel dehydratase of the fatty acid synthase type II critical for ketomycolic acid biosynthesis and virulence of Mycobacterium tuberculosis

The fatty acid synthase type II (FAS-II) multienzyme system builds the main chain of mycolic acids (MAs), important lipid pathogenicity factors of Mycobacterium tuberculosis (Mtb). Due to their original structure, the identification of the (3 R)-hydroxyacyl-ACP dehydratases, HadAB and HadBC, of Mtb FAS-II complex required in-depth work. Here, we report the discovery of a third dehydratase protein, HadD_Mtb (Rv0504c), whose gene is non-essential and sits upstream of cmaA2 encoding a cyclopropane synthase dedicated to keto- and methoxy-MAs. HadD_Mtb deletion triggered a marked change in Mtb keto-MA content and size distribution, deeply impacting the production of full-size molecules. Furthermore, abnormal MAs, likely generated from 3-hydroxylated intermediates, accumulated. These data strongly suggest that HadD_Mtb catalyzes the 3-hydroxyacyl dehydratation step of late FAS-II elongation cycles during keto-MA biosynthesis. Phenotyping of Mtb hadD deletion mutant revealed the influence of HadD_Mtb on the planktonic growth, colony morphology and biofilm structuration, as well as on low temperature tolerance. Importantly, HadD_Mtb has a strong impact on Mtb virulence in the mouse model of infection. The effects of the lack of HadD_Mtb observed both in vitro and in vivo designate this protein as a bona fide target for the development of novel anti-TB intervention strategies.

Draft Genome Sequence of an Isolate of Extensively Drug-Resistant Mycobacterium tuberculosis from Nepal

Extensively drug-resistant (XDR) Mycobacterium tuberculosis has become a challenge to the treatment of tuberculosis (TB) in several countries, including Nepal. Here, we report for the first time the draft genome sequence of an isolate of XDR-TB collected in Nepal and describe single-nucleotide variations associated with its extensively drug-resistant phenotype.

Extensively drug-resistant (XDR) Mycobacterium tuberculosis has become a challenge to the treatment of tuberculosis (TB) in several countries, including Nepal. Here, we report for the first time the draft genome sequence of an isolate of XDR-TB collected in Nepal and describe single-nucleotide variations associated with its extensively drug-resistant phenotype.

Fluoroquinolones and isoniazid-resistant tuberculosis: implications for the 2018 WHO guidance

Introduction

2018 World Health Organization (WHO) guidelines for the treatment of isoniazid (H)-resistant (Hr) tuberculosis recommend a four-drug regimen: rifampicin (R), ethambutol (E), pyrazinamide (Z) and levofloxacin (Lfx), with or without H ([H]RZE-Lfx). This is used once Hr is known, such that patients complete 6 months of Lfx (≥6[H]RZE-6Lfx). This cohort study assessed the impact of fluoroquinolones (Fq) on treatment effectiveness, accounting for Hr mutations and degree of phenotypic resistance.

Methods

This was a retrospective cohort study of 626 Hr tuberculosis patients notified in London, 2009–2013. Regimens were described and logistic regression undertaken of the association between regimen and negative regimen-specific outcomes (broadly, death due to tuberculosis, treatment failure or disease recurrence).

Results

Of 594 individuals with regimen information, 330 (55.6%) were treated with (H)RfZE (Rf=rifamycins) and 211 (35.5%) with (H)RfZE-Fq. The median overall treatment period was 11.9 months and median Z duration 2.1 months. In a univariable logistic regression model comparing (H)RfZE with and without Fqs, there was no difference in the odds of a negative regimen-specific outcome (baseline (H)RfZE, cluster-specific odds ratio 1.05 (95% CI 0.60–1.82), p=0.87; cluster NHS trust). Results varied minimally in a multivariable model. This odds ratio dropped (0.57, 95% CI 0.14–2.28) when Hr genotype was included, but this analysis lacked power (p=0.42).

Conclusions

In a high-income setting, we found a 12-month (H)RfZE regimen with a short Z duration to be similarly effective for Hr tuberculosis with or without a Fq. This regimen may result in fewer adverse events than the WHO recommendations.

WHO has assessed regimen recommendations for isoniazid-resistant TB to be of very low certainty. The addition of fluoroquinolones to a 12-month (isoniazid, rifamycin, ethambutol, short-duration pyrazinamide) regimen may be unnecessary in certain settings.http://bit.ly/2XoTgNL

Assessing capreomycin resistance on tlyA deficient and point mutation (G695A) Mycobacterium tuberculosis strains using multi-omics analysis

Capreomycin (CAP), a cyclic peptide antibiotic, is considered to be an ideal second-line drug for tuberculosis (TB). However, in the past few years, the emergence of more CAP-resistant (CAP^r) TB patients has limited its use. Although it has been reported that CAP resistance to Mycobacterium tuberculosis (Mtb) is associated with rrs or tlyA mutation, the exact mechanism of CAP^r Mtb strains, especially the mechanism associated with tlyA deficient or mutation, is not fully understood. Herein, we utilized a multi-omics (genome, proteome, and metabolome) approach to assess CAP resistance on tlyA deficient CAP^r Mtb strains (CAP^r1) and tlyA point mutation CAP^r Mtb strains (CAP^r2) that we established for the first time in vitro to investigate the CAP-resistant mechanism. Our results showed that the CAP^r1 strains (> 40 μg/ml) was more resistant to CAP than the CAP^r2 strains (G695A, 10 μg/ml). Furthermore, multi-omics analysis indicated that the CAP^r1 strains exhibited greater drug tolerance than the CAP^r2 strains may be associated with the weakening of S-adenosyl-L-methionine-dependent methyltransferase (AdoMet-MT) activity and abnormal membrane lipid metabolism such as suppression of fatty acid metabolism, promotion of glycolipid phospholipid and glycerolipid metabolism. As a result, these studies reveal a new mechanism for CAP resistance to tlyA deficient or mutation Mtb strains, and may be helpful in developing new therapeutic approaches to prevent Mtb resistance to CAP.

Kinase Targets for Mycolic Acid Biosynthesis in Mycobacterium tuberculosis

BACKGROUND

Mycolic acids (MAs) are the characteristic, integral building blocks for the mycomembrane belonging to the insidious bacterial pathogen Mycobacterium tuberculosis (M.tb). These C60-C90 long α-alkyl-β-hydroxylated fatty acids provide protection to the tubercle bacilli against the outside threats, thus allowing its survival, virulence and resistance to the current antibacterial agents. In the post-genomic era, progress has been made towards understanding the crucial enzymatic machineries involved in the biosynthesis of MAs in M.tb. However, gaps still remain in the exact role of the phosphorylation and dephosphorylation of regulatory mechanisms within these systems. To date, a total of 11 serine-threonine protein kinases (STPKs) are found in M.tb. Most enzymes implicated in the MAs synthesis were found to be phosphorylated in vitro and/or in vivo. For instance, phosphorylation of KasA, KasB, mtFabH, InhA, MabA, and FadD32 downregulated their enzymatic activity, while phosphorylation of VirS increased its enzymatic activity. These observations suggest that the kinases and phosphatases system could play a role in M.tb adaptive responses and survival mechanisms in the human host. As the mycobacterial STPKs do not share a high sequence homology to the human's, there have been some early drug discovery efforts towards developing potent and selective inhibitors.

OBJECTIVE

Recent updates to the kinases and phosphatases involved in the regulation of MAs biosynthesis will be presented in this mini-review, including their known small molecule inhibitors.

CONCLUSION

Mycobacterial kinases and phosphatases involved in the MAs regulation may serve as a useful avenue for antitubercular therapy.

Advance in Research on Mycobacterium tuberculosis FabG4 and Its Inhibitor

Increasing evidence from recent reports of drug-resistant mycobacterial strains poses a challenge worldwide. Drug-resistant strains often undergo mutations, adopt alternative pathways, and express drug efflux pumps to reduce or eliminate drug doses. Besides these intrinsic resistance mechanisms, bacteria can evade drug doses by forming biofilms. Biofilms are the concerted growth of adherent microorganisms, which can also be formed at the air-water interface. The growth is supported by the extracellular polymer matrix which is self-produced by the microorganisms. Reduced metabolic activity in a nutrient-deficient environment in the biofilm may cause the microorganisms to take alternative pathways that can make the microorganisms recalcitrant to the drug doses. Recent works have shown that Mycobacterium tuberculosis expresses several proteins during its growth in biofilm, those when deleted, did not show any effect on mycobacterial growth in normal nutrient-sufficient conditions. Studying these unconventional proteins in mycobacterial biofilms is therefore of utmost importance. In this article, I will discuss one such mycobacterial biofilm-related protein FabG4 that is recently shown to be important for mycobacterial survival in the presence of antibiotic stressors and limited nutrient condition. In an attempt to find more effective FabG4 inhibitors and its importance in biofilm forming M. tuberculosis, present knowledge about FabG4 and its known inhibitors are discussed. Based on the existing data, a putative role of FabG4 is also suggested.

Structural rearrangements occurring upon cofactor binding in the Mycobacterium smegmatis β-ketoacyl-acyl carrier protein reductase MabA

In mycobacteria, the ketoacyl-acyl carrier protein (ACP) reductase MabA (designated FabG in other bacteria) catalyzes the NADPH-dependent reduction of β-ketoacyl-ACP substrates to β-hydroxyacyl-ACP products. This first reductive step in the fatty-acid biosynthesis elongation cycle is essential for bacteria, which makes MabA/FabG an interesting drug target. To date, however, very few molecules targeting FabG have been discovered and MabA remains the only enzyme of the mycobacterial type II fatty-acid synthase that lacks specific inhibitors. Despite the existence of several MabA/FabG crystal structures, the structural rearrangement that occurs upon cofactor binding is still not fully understood. Therefore, unlocking this knowledge gap could help in the design of new inhibitors. Here, high-resolution crystal structures of MabA from Mycobacterium smegmatis in its apo, NADP⁺-bound and NADPH-bound forms are reported. Comparison of these crystal structures reveals the structural reorganization of the lid region covering the active site of the enzyme. The crystal structure of the apo form revealed numerous residues that trigger steric hindrance to the binding of NADPH and substrate. Upon NADPH binding, these residues are pushed away from the active site, allowing the enzyme to adopt an open conformation. The transition from an NADPH-bound to an NADP⁺-bound form is likely to facilitate release of the product. These results may be useful for subsequent rational drug design and/or for in silico drug-screening approaches targeting MabA/FabG.

Molecular modeling studies and in vitro screening of dihydrorugosaflavonoid and its derivatives against Mycobacterium tuberculosis

Novel drug regimens against tuberculosis (TB) are urgently needed and may be developed by targeting essential enzymes of Mtb that sustain the pathogenicity of tuberculosis. Dihydrorugosaflavonoid interacted with the active pocket of MabA and PanK.

S-Enantiomer of the Antitubercular Compound S006-830 Complements Activity of Frontline TB Drugs and Targets Biogenesis of Mycobacterium tuberculosis Cell Envelope

A synthetic molecule S006-830, belonging to the class of thiophene-containing trisubstituted methanes, had shown good in vitro and in vivo bactericidal activity against drug-sensitive and drug-resistant Mycobacterium tuberculosis (Mtb). The molecule had also shown good druglike pharmacokinetic properties. However, S006-830 is a racemic mixture of two enantiomers, one of which could possess a better pharmacological profile than the other. We purified both the enantiomers on a chiral column and observed that S-enantiomer has a significantly higher inhibitory and cidal activity against Mtb than the R-enantiomer. Action of S-S006-830 was "synergistic" for rifampicin and "additive" for isoniazid and ethambutol. The combination of S-S006-830 and rifampicin produced 100% kill of Mtb within 8 days. In a chemical proteomics approach using matrix-bound compound to pull down its target protein(s) from Mtb membrane, FabG4 (β-ketoacyl CoA reductase, EC 1.1.1.100) emerged as the most likely target for S-S006-830. In target validation assays, the compound exhibited 2-fold higher inhibitory concentration for an Mtb construct overexpressing FabG4. In addition, it inhibited mycolic acid biosynthesis and formation of biofilms by Mtb. Molecular docking of S-S006-830 with FabG4 was consistent with the experimental data. These results support the development of S-S006-830 as a novel lead against tuberculosis.

Disruption of key NADH-binding pocket residues of the Mycobacterium tuberculosis InhA affects DD-CoA binding ability

Tuberculosis (TB) is a global health problem that affects over 10 million people. There is an urgent need to develop novel antimicrobial therapies to combat TB. To achieve this, a thorough understanding of key validated drug targets is required. The enoyl reductase InhA, responsible for synthesis of essential mycolic acids in the mycobacterial cell wall, is the target for the frontline anti-TB drug isoniazid. To better understand the activity of this protein a series of mutants, targeted to the NADH co-factor binding pocket were created. Residues P193 and W222 comprise a series of hydrophobic residues surrounding the cofactor binding site and mutation of both residues negatively affect InhA function. Construction of an M155A mutant of InhA results in increased affinity for NADH and DD-CoA turnover but with a reduction in V_max for DD-CoA, impairing overall activity. This suggests that NADH-binding geometry of InhA likely permits long-range interactions between residues in the NADH-binding pocket to facilitate substrate turnover in the DD-CoA binding region of the protein. Understanding the precise details of substrate binding and turnover in InhA and how this may affect protein-protein interactions may facilitate the development of improved inhibitors enabling the development of novel anti-TB drugs.

Binding of NADP+ triggers an open-to-closed transition in a mycobacterial FabG β-ketoacyl-ACP reductase

The ketoacyl-acyl carrier protein (ACP) reductase FabG catalyzes the NADPH/NADH dependent reduction of β-ketoacyl-ACP substrates to β-hydroxyacyl-ACP products, the first reductive step in the fatty acid biosynthesis elongation cycle. FabG proteins are ubiquitous in bacteria and are part of the type II fatty acid synthase system. Mining the Mycobacterium smegmatis genome uncovered several putative FabG-like proteins. Among them, we identified M. smegmatis MSMEG_6753 whose gene was found adjacent to MSMEG_6754, encoding a recently characterized enoyl-CoA dehydratase, and to MSMEG_6755, encoding another potential reductase. Recombinantly expressed and purified MSMEG_6753 exhibits ketoacyl reductase activity in the presence of acetoacetyl-CoA and NADPH. This activity was subsequently confirmed by functional complementation studies in a fabG thermosensitive Escherichia coli mutant. Furthermore, comparison of the apo and the NADP⁺-bound MSMEG_6753 crystal structures showed that cofactor binding induces a closed conformation of the protein. A ΔMSMEG_6753 deletion mutant could be generated in M. smegmatis, indicating that this gene is dispensable for mycobacterial growth. Overall, these results showcase the diversity of FabG-like proteins in mycobacteria and new structural features regarding the catalytic mechanism of this important family of enzymes that may be of importance for the rational design of specific FabG inhibitors.

Mycobacterial cell wall biosynthesis: a multifaceted antibiotic target

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB), is recognized as a global health emergency as promoted by the World Health Organization. Over 1 million deaths per year, along with the emergence of multi- and extensively-drug resistant strains of Mtb, have triggered intensive research into the pathogenicity and biochemistry of this microorganism, guiding the development of anti-TB chemotherapeutic agents. The essential mycobacterial cell wall, sharing some common features with all bacteria, represents an apparent ‘Achilles heel’ that has been targeted by TB chemotherapy since the advent of TB treatment. This complex structure composed of three distinct layers, peptidoglycan, arabinogalactan and mycolic acids, is vital in supporting cell growth, virulence and providing a barrier to antibiotics. The fundamental nature of cell wall synthesis and assembly has rendered the mycobacterial cell wall as the most widely exploited target of anti-TB drugs. This review provides an overview of the biosynthesis of the prominent cell wall components, highlighting the inhibitory mechanisms of existing clinical drugs and illustrating the potential of other unexploited enzymes as future drug targets.

Identification of KasA as the cellular target of an anti-tubercular scaffold

Phenotypic screens for bactericidal compounds are starting to yield promising hits against tuberculosis. In this regard, whole-genome sequencing of spontaneous resistant mutants generated against an indazole sulfonamide (GSK3011724A) identifies several specific single-nucleotide polymorphisms in the essential Mycobacterium tuberculosis β-ketoacyl synthase (kas) A gene. Here, this genomic-based target assignment is confirmed by biochemical assays, chemical proteomics and structural resolution of a KasA-GSK3011724A complex by X-ray crystallography. Finally, M. tuberculosis GSK3011724A-resistant mutants increase the in vitro minimum inhibitory concentration and the in vivo 99% effective dose in mice, establishing in vitro and in vivo target engagement. Surprisingly, the lack of target engagement of the related β-ketoacyl synthases (FabH and KasB) suggests a different mode of inhibition when compared with other Kas inhibitors of fatty acid biosynthesis in bacteria. These results clearly identify KasA as the biological target of GSK3011724A and validate this enzyme for further drug discovery efforts against tuberculosis.

Molecular docking studies on InhA, MabA and PanK enzymes from Mycobacterium tuberculosis of ellagic acid derivatives from Ludwigia adscendens and Trewia nudiflora

Purpose

There is an urgent need to discover and develop new drugs to combat Mycobacterium tuberculosis, the causative agent of tuberculosis (TB) in humans. In recent years, there has been a renewed interest in the discovery of new anti-TB agents from natural sources. In the present investigation, molecular docking studies were carried out on two ellagic acid derivatives, namely pteleoellagic acid (1) isolated from Ludwigia adscendens, and 3,3′-di-O-methyl ellagic acid 4-O-α-rhamnopyranoside (2) isolated from Trewia nudiflora, to investigate their binding to two enzymes involved in M. tuberculosis cell wall biogenesis, namely 2-trans-enoyl-ACP reductase (InhA) and β-ketoacyl-ACP reductase (MabA), and to pantothenate kinase (PanK type I) involved in the biosynthesis of coenzyme A, essential for the growth of M. tuberculosis.

Methods

Molecular docking experiments were performed using AutoDock Vina.

The crystal structures of InhA, MabA and PanK were retrieved from the RCSB Protein Data Bank (PDB). Isonicotinic-acyl-NADH for InhA and MabA, and triazole inhibitory compound for PanK, were used as references.

Results

Pteleoellagic acid showed a high docking score, estimated binding free energy of −9.4 kcal/mol, for the MabA enzyme comparable to the reference compound isonicotinic-acyl-NADH.

Conclusions

Knowledge on the molecular interactions of ellagic acid derivatives with essential M. tuberculosis targets could prove a useful tool for the design and development of future anti-TB drugs.

Electronic supplementary material

The online version of this article (doi:10.1186/s40203-015-0014-1) contains supplementary material, which is available to authorized users.

Dissecting the Structural Elements for the Activation of β-Ketoacyl-(Acyl Carrier Protein) Reductase from Vibrio cholerae

β-Ketoacyl-(acyl carrier protein) reductase (FabG) catalyzes the key reductive reaction in the elongation cycle of fatty acid synthesis (FAS), which is a vital metabolic pathway in bacteria and a promising target for new antibiotic development. The activation of the enzyme is usually linked to the formation of a catalytic triad and cofactor binding, and crystal structures of FabG from different organisms have been captured in either the active or inactive conformation. However, the structural elements which enable activation of FabG require further exploration. Here we report the findings of structural, enzymatic, and binding studies of the FabG protein found in the causative agent of cholera, Vibrio cholerae (vcFabG). vcFabG exists predominantly as a dimer in solution and is able to self-associate to form tetramers, which is the state seen in the crystal structure. The formation of the tetramer may be promoted by the presence of the cofactor NADP(H). The transition between the dimeric and tetrameric states of vcFabG is related to changes in the conformations of the α4/α5 helices on the dimer-dimer interface. Two glycine residues adjacent to the dimer interface (G92 and G141) are identified to be the hinge for the conformational changes, while the catalytic tyrosine (Y155) and a glutamine residue that forms hydrogen bonds to both loop β4-α4 and loop β5-α5 (Q152) stabilize the active conformation. The functions of the aforementioned residues were confirmed by binding and enzymatic assays for the corresponding mutants.

IMPORTANCE

This paper describes the results of structural, enzymatic, and binding studies of FabG from Vibrio cholerae (vcFabG). In this work, we dissected the structural elements responsible for the activation of vcFabG. The structural information provided here is essential for the development of antibiotics specifically targeting bacterial FabG, especially for the multidrug-resistant strains of V. cholerae.

The Mycobacterium tuberculosis relBE toxin:antitoxin genes are stress-responsive modules that regulate growth through translation inhibition

Toxin-antitoxin (TA) genes are ubiquitous among bacteria and are associated with persistence and dormancy. Following exposure to unfavorable environmental stimuli, several species (Escherichia coli, Staphylococcus aureus, Myxococcus xanthus) employ toxin proteins such as RelE and MazF to downregulate growth or initiate cell death. Mycobacterium tuberculosis possesses three Rel TA modules (Rel Mtb ): RelBE Mtb , RelFG Mtb and RelJK Mtb (Rv1246c-Rv1247c, Rv2865-Rv2866, and Rv3357-Rv3358, respectively), which inhibit mycobacterial growth when the toxin gene (relE, relG, relK) is expressed independently of the antitoxin gene (relB, relF, relJ). In the present study, we examined the in vivo mechanism of the RelE Mtb toxin protein, the impact of RelE Mtb on M. tuberculosis physiology and the environmental conditions that regulate all three rel Mtb modules. RelE Mtb negatively impacts growth and the structural integrity of the mycobacterial envelope, generating cells with aberrant forms that are prone to extensive aggregation. At a time coincident with growth defects, RelE Mtb mediates mRNA degradation in vivo resulting in significant changes to the proteome. We establish that rel Mtb modules are stress responsive, as all three operons are transcriptionally activated following mycobacterial exposure to oxidative stress or nitrogen-limiting growth environments. Here we present evidence that the rel Mtb toxin:antitoxin family is stress-responsive and, through the degradation of mRNA, the RelE Mtb toxin influences the growth, proteome and morphology of mycobacterial cells.

The Molecular Genetics of Mycolic Acid Biosynthesis

Mycolic acids are major and specific long-chain fatty acids that represent essential components of the Mycobacterium tuberculosis cell envelope. They play a crucial role in the cell wall architecture and impermeability, hence the natural resistance of mycobacteria to most antibiotics, and represent key factors in mycobacterial virulence. Biosynthesis of mycolic acid precursors requires two types of fatty acid synthases (FASs), the eukaryotic-like multifunctional enzyme FAS I and the acyl carrier protein (ACP)–dependent FAS II systems, which consists of a series of discrete mono-functional proteins, each catalyzing one reaction in the pathway. Unlike FAS II synthases of other bacteria, the mycobacterial FAS II is incapable of de novo fatty acid synthesis from acetyl-coenzyme A, but instead elongates medium-chain-length fatty acids previously synthesized by FAS I, leading to meromycolic acids. In addition, mycolic acid subspecies with defined biological properties can be distinguished according to the chemical modifications decorating the meromycolate. Nearly all the genetic components involved in both elongation and functionalization of the meromycolic acid have been identified and are generally clustered in distinct transcriptional units. A large body of information has been generated on the enzymology of the mycolic acid biosynthetic pathway and on their genetic and biochemical/structural characterization as targets of several antitubercular drugs. This chapter is a comprehensive overview of mycolic acid structure, function, and biosynthesis. Special emphasis is given to recent work addressing the regulation of mycolic acid biosynthesis, adding new insights to our understanding of how pathogenic mycobacteria adapt their cell wall composition in response to environmental changes.

Cloning, overexpression, purification, crystallization and preliminary X-ray diffraction analysis of Rv0241c (HtdX) from Mycobacterium tuberculosis H37Rv

Rv0241c (HtdX) is a putative (3R)-hydroxyacyl-CoA dehydratase of Mycobacterium tuberculosis. The htdX gene belongs to a conserved operon and is expressed in mycobacteria in the presence of several fatty-acid synthase II drugs. To elucidate the structure of HtdX, the protein was cloned, overexpressed, purified to homogeneity and crystallized. The protein was crystallized from two conditions: (i) 3 M sodium chloride, 0.1 M Na HEPES pH 8.0 and (ii) 2.5 M sodium chloride, 0.1 M Tris-HCl pH 8.5. A complete diffraction data set was collected from crystals from both conditions. The crystal from the first condition diffracted to 2.3 Å resolution and belonged to space group I41, with unit-cell parameters a=b=61.51, c=143.81 Å. Crystals from the second condition diffracted to 3.1 Å resolution and belonged to space group P4₃2₁2 or P4₁2₁2, with unit-cell parameters a=b=63.67, c=140.88 Å. Both crystals contained one molecule in the asymmetric unit.

Evaluation of the potential role of a new mutation in mabA in modifying the response of Mycobacterium tuberculosis to isoniazid

A new mutation in mabA, Thr4Ile, was identified in a Mycobacterium tuberculosis isolate from a patient whose culture remained positive after treatment. The same mutation was found in another 5 patients infected by different strains. A putative role for this mutation in the process of diminishing susceptibility to isoniazid is evaluated.

Crystal structure of hexanoyl-CoA bound to β-ketoacyl reductase FabG4 of Mycobacterium tuberculosis

FabGs, or β-oxoacyl reductases, are involved in fatty acid synthesis. The reaction entails NADPH/NADH-mediated conversion of β-oxoacyl-ACP (acyl-carrier protein) into β-hydroxyacyl-ACP. HMwFabGs (high-molecular-weight FabG) form a phylogenetically separate group of FabG enzymes. FabG4, an HMwFabG from Mycobacterium tuberculosis, contains two distinct domains, an N-terminal 'flavodoxintype' domain and a C-terminal oxoreductase domain. The catalytically active C-terminal domain utilizes NADH to reduce β-oxoacyl-CoA to β-hydroxyacyl-CoA. In the present study the crystal structures of the FabG4-NADH binary complex and the FabG4-NAD+-hexanoyl-CoA ternary complex have been determined to understand the substrate specificity and catalytic mechanism of FabG4. This is the first report to demonstrate how FabG4 interacts with its coenzyme NADH and hexanoyl-CoA that mimics an elongating fattyacyl chain covalently linked with CoA. Structural analysis shows that the binding of hexanoyl-CoA within the active site cavity of FabG significantly differs from that of the C16 fattyacyl substrate bound to mycobacterial FabI [InhA (enoyl-ACP reductase)]. The ternary complex reveals that both loop I and loop II interact with the phosphopantetheine moiety of CoA or ACP to align the covalently linked fattyacyl substrate near the active site. Structural data ACP inhibition studies indicate that FabG4 can accept both CoA- and ACP-based fattyacyl substrates. We have also shown that in the FabG4 dimer Arg146 and Arg445 of one monomer interact with the C-terminus of the second monomer to play pivotal role in substrate association and catalysis.

Role of Serine140 in the mode of action of Mycobacterium tuberculosis β-ketoacyl-ACP Reductase (MabA)

Background

Tuberculosis (TB) still remains one of the most deadly infectious diseases in the world. Mycobacterium tuberculosis β-ketoacyl-ACP Reductase (MabA) is a member of the fatty acid elongation system type II, providing precursors of mycolic acids that are essential to the bacterial cell growth and survival. MabA has been shown to be essential for M. tuberculosis survival and to play a role in intracellular signal transduction of bacilli.

Findings

Here we describe site-directed mutagenesis, recombinant protein expression and purification, steady-state kinetics, fluorescence spectroscopy, and molecular modeling for S140T and S140A mutant MabA enzymes. No enzyme activity could be detected for S140T and S140A. Although the S140T protein showed impaired NADPH binding, the S140A mutant could bind to NADPH. Computational predictions for NADPH binding affinity to WT, S140T and S140A MabA proteins were consistent with fluorescence spectroscopy data.

Conclusions

The results suggest that the main role of the S140 side chain of MabA is in catalysis. The S140 side chain appears to also play an indirect role in NADPH binding. Interestingly, NADPH titrations curves shifted from sigmoidal for WT to hyperbolic for S140A, suggesting that the S140 residue may play a role in displacing the pre-existing equilibrium between two forms of MabA in solution. The results here reported provide a better understanding of the mode of action of MabA that should be useful to guide the rational (function-based) design of inhibitors of MabA enzyme activity which, hopefully, could be used as lead compounds with anti-TB action.

Crystallization and preliminary X-ray diffraction analysis of the high molecular weight ketoacyl reductase FabG4 complexed with NADH

FabG4 from Mycobacterium tuberculosis belongs to the high molecular weight ketoacyl reductases (HMwFabGs). The enzyme requires NADH for β-ketoacyl reductase activity. The protein was overexpressed, purified to homogeneity and crystallized as a FabG4-NADH complex. A mountable FabG4:NADH complex crystal diffracted to 2.59 Å resolution and belonged to space group P1, with unit-cell parameters a = 63.07, b = 71.03, c = 92.92 Å, α = 105.02, β = 97.06, γ = 93.66°. The Matthews coefficient suggested the presence of four monomers in the unit cell. In addition, a self-rotation function revealed the presence of two twofold NCS axes and one fourfold NCS axis. At χ = 180° the highest peak corresponds to the twofold NCS between two monomers, whereas the second peak corresponds to the twofold NCS between two dimers.

The Mycobacterium tuberculosis FAS-II dehydratases and methyltransferases define the specificity of the mycolic acid elongation complexes

BACKGROUND

The human pathogen Mycobacterium tuberculosis (Mtb) has the originality of possessing a multifunctional mega-enzyme FAS-I (Fatty Acid Synthase-I), together with a multi-protein FAS-II system, to carry out the biosynthesis of common and of specific long chain fatty acids: the mycolic acids (MA). MA are the main constituents of the external mycomembrane that represents a tight permeability barrier involved in the pathogenicity of Mtb. The MA biosynthesis pathway is essential and contains targets for efficient antibiotics. We have demonstrated previously that proteins of FAS-II interact specifically to form specialized and interconnected complexes. This finding suggested that the organization of FAS-II resemble to the architecture of multifunctional mega-enzyme like the mammalian mFAS-I, which is devoted to the fatty acid biosynthesis.

PRINCIPAL FINDINGS

Based on conventional and reliable studies using yeast-two hybrid, yeast-three-hybrid and in vitro Co-immunoprecipitation, we completed here the analysis of the composition and architecture of the interactome between the known components of the Mtb FAS-II complexes. We showed that the recently identified dehydratases HadAB and HadBC are part of the FAS-II elongation complexes and may represent a specific link between the core of FAS-II and the condensing enzymes of the system. By testing four additional methyltransferases involved in the biosynthesis of mycolic acids, we demonstrated that they display specific interactions with each type of complexes suggesting their coordinated action during MA elongation.

SIGNIFICANCE

These results provide a global update of the architecture and organization of a FAS-II system. The FAS-II system of Mtb is organized in specialized interconnected complexes and the specificity of each elongation complex is given by preferential interactions between condensing enzymes and dehydratase heterodimers. This study will probably allow defining essential and specific interactions that correspond to promising targets for Mtb FAS-II inhibitors.