Characterization and function of Mycobacterium tuberculosis H37Rv Lipase Rv1076 (LipU)

Mycobacterium tuberculosis Rv2617c is involved in stress response and phage infection resistance

Mycobacterium tuberculosis (M. tuberculosis) is the pathogen of human tuberculosis (TB). Resistance to numerous in vivo stresses, including oxidative stress, is determinant for M. tuberculosis intracellular survival, and understanding associated mechanisms is crucial for developing new therapeutic strategies. M. tuberculosis Rv2617c has been associated with oxidative stress response when interacting with other proteins in M. tuberculosis; however, its functional promiscuity and underlying molecular mechanisms remain elusive. In this study, we investigated the phenotypic changes of Mycobacterium smegmatis (M. smegmatis) expressing Rv2617c (Ms_Rv2617c) and its behavior in the presence of various in vitro stresses and phage infections. We found that Rv2617c conferred resistance to SDS and diamide while sensitizing M. smegmatis to oxidative stress (H2O2) and altered mycobacterial phenotypic properties (single-cell clone and motility), suggestive of reprogrammed mycobacterial cell wall lipid contents exemplified by increased cell wall permeability. Interestingly, we also found that Rv2617c promoted M. smegmatis resistance to infection by phages (SWU1, SWU2, D29, and TM4) and kept phage TM4 from destroying mycobacterial biofilms. Our findings provide new insights into the role of Rv2617c in resistance to oxide and acid stresses and report for the first time on its role in phage resistance in Mycobacterium.

Roles of Lipolytic enzymes in Mycobacterium tuberculosis pathogenesis

Mycobacterium tuberculosis (Mtb) is a bacterial pathogen that can endure for long periods in an infected patient, without causing disease. There are a number of virulence factors that increase its ability to invade the host. One of these factors is lipolytic enzymes, which play an important role in the pathogenic mechanism of Mtb. Bacterial lipolytic enzymes hydrolyze lipids in host cells, thereby releasing free fatty acids that are used as energy sources and building blocks for the synthesis of cell envelopes, in addition to regulating host immune responses. This review summarizes the relevant recent studies that used in vitro and in vivo models of infection, with particular emphasis on the virulence profile of lipolytic enzymes in Mtb. A better understanding of these enzymes will aid the development of new treatment strategies for TB. The recent work done that explored mycobacterial lipolytic enzymes and their involvement in virulence and pathogenicity was highlighted in this study. Lipolytic enzymes are expected to control Mtb and other intracellular pathogenic bacteria by targeting lipid metabolism. They are also potential candidates for the development of novel therapeutic agents.

Comparative modelling, molecular docking and immobilization studies on Rhizopus oryzae lipase: evaluation of potentials for fatty acid methyl esters synthesis

Elucidation of lipase-substrate interactions will guide the proper industrial use and applicability of the enzyme. The aim of this study was to predict the 3 D structure of Rhizopus oryzae ZAC3 (RoZAC3) lipase, study its interactions with some natural substrates and evaluate the feasibility of fatty acid methyl esters (FAME) production by the immobilized lipase. Protein identification of RoZAC3 lipase was carried out using LC-MS/MS. The 3 D structure of the lipase was built using homology modelling and natural substrates such as tributyrin, tripalmitin and triolein were docked to the optimized 3 D model for investigation of enzyme-ligand interactions. RoZAC3 lipase, immobilized by adsorption on Lewatit VP OC 1600 was applied in the synthesis of fatty acid methyl esters (FAME). From the phylogenetic analysis, it was observed that RoZAC3 lipase was closely related (48%) to Rhizopus javanicus lipase (Q7M4U7). The predicted 3 D model was validated using the SWISS model validation server. Ramachandran and ERRAT plots were used to assess the amino acid environment and overall quality of the model. From the docking studies, the values of the binding energies obtained for tributyrin, tripalmitin and triolein were - 5.37, -5.27 and -5.77 respectively. At an enzyme:immobilization support ratio of 50 mg/g, transesterification reaction duration of 18 h and a temperature of 40 oC, the conversion reached above 80%. The molecular docking studies provided information on the interaction/modifications between the RoZAC3 lipase and triacylglycerols that can be exploited for numerous applications. The immobilized lipase could serve in hydro-esterification reactions adaptable for biodiesel production.Communicated by Ramaswamy H. Sarma.

The cause-effect relation of tuberculosis on incidence of diabetes mellitus

Tuberculosis (TB) is one of the oldest human diseases and is one of the major causes of mortality and morbidity across the Globe. Mycobacterium tuberculosis (Mtb), the causal agent of TB is one of the most successful pathogens known to mankind. Malnutrition, smoking, co-infection with other pathogens like human immunodeficiency virus (HIV), or conditions like diabetes further aggravate the tuberculosis pathogenesis. The association between type 2 diabetes mellitus (DM) and tuberculosis is well known and the immune-metabolic changes during diabetes are known to cause increased susceptibility to tuberculosis. Many epidemiological studies suggest the occurrence of hyperglycemia during active TB leading to impaired glucose tolerance and insulin resistance. However, the mechanisms underlying these effects is not well understood. In this review, we have described possible causal factors like inflammation, host metabolic changes triggered by tuberculosis that could contribute to the development of insulin resistance and type 2 diabetes. We have also discussed therapeutic management of type 2 diabetes during TB, which may help in designing future strategies to cope with TB-DM cases.

2,4-Disubstituted pyridine derivatives are effective against intracellular and biofilm-forming tubercle bacilli

It was recently reported that 4-substituted picolinohydrazonamides carrying hydrophilic cyclic amines, such as morpholine and pyrrolidine, at the end of their thiosemicarbazide chain have potent antimycobacterial activity in vitro at concentrations below 1 μg/ml. Here, two selected compounds, 2,4-disubstituted pyridine derivatives 11 and 15, revealed significant bactericidal activity against Mycobacterium tuberculosis localized intracellularly within human macrophages, as well as against biofilm-forming tubercle bacilli. Mutants were selected that were resistant to the investigated compounds at an efficiency similar to that identified in the presence of the first line antituberculosis drug rifampicin. The resistant mutants were viable in the presence of the tested compounds exclusively on solid media. Genome-wide sequencing of the mutants selected in the presence of compound 11 revealed the accumulation of nonsynonymous mutations in the mmpR5 gene encoding a transcriptional repressor of the MmpS5-MmpL5 efflux pump, whose upregulation has been associated with bedaquiline resistance. The depletion of MmpR5 in wild-type M. tuberculosis using CRISPR–Cas9 technology increased the resistance of this strain to compound 11. Mass spectrometry-based proteomics (LC–MS/MS) of wild-type tubercle bacilli growing in subinhibitory concentrations of compounds 11 or 15 revealed 15 overproduced proteins not detectable in the control cells, including virulence-related proteins.

Transcriptional adaptation of Mycobacterium ulcerans in an original mouse model: New insights into the regulation of mycolactone

Mycobacterium ulcerans is the causal agent of Buruli ulcer, a chronic infectious disease and the third most common mycobacterial disease worldwide. Without early treatment, M. ulcerans provokes massive skin ulcers, caused by the mycolactone toxin, its main virulence factor. However, spontaneous healing may occur in Buruli ulcer patients several months or years after the disease onset. We have shown, in an original mouse model, that bacterial load remains high and viable in spontaneously healed tissues, with a switch of M. ulcerans to low levels of mycolactone production, adapting its strategy to survive in such a hostile environment. This original model offers the possibility to investigate the regulation of mycolactone production, by using an RNA-seq strategy to study bacterial adaptation during mouse infection. Pathway analysis and characterization of the tissue environment showed that the bacillus adapted to its new environment by modifying its metabolic activity and switching nutrient sources. Thus, M. ulcerans ensures its survival in healing tissues by reducing its secondary metabolism, leading to an inhibition of mycolactone synthesis. These findings shed new light on mycolactone regulation and pave the way for new therapeutic strategies.

On the Identification of Clinically Relevant Bacterial Amino Acid Changes at the Whole Genome Level Using Auto-PSS-Genome

The identification of clinically relevant bacterial amino acid changes can be performed using different methods aimed at the identification of genes showing positively selected amino acid sites (PSS). Nevertheless, such analyses are time consuming, and the frequency of genes showing evidence for PSS can be low. Therefore, the development of a pipeline that allows the quick and efficient identification of the set of genes that show PSS is of interest. Here, we present Auto-PSS-Genome, a Compi-based pipeline distributed as a Docker image, that automates the process of identifying genes that show PSS using three different methods, namely codeML, FUBAR, and omegaMap. Auto-PSS-Genome accepts as input a set of FASTA files, one per genome, containing all coding sequences, thus minimizing the work needed to conduct positively selected sites analyses. The Auto-PSS-Genome pipeline identifies orthologous gene sets and corrects for multiple possible problems in input FASTA files that may prevent the automated identification of genes showing PSS. A FASTA file containing all coding sequences can also be given as an external global reference, thus easing the comparison of results across species, when gene names are different. In this work, we use Auto-PSS-Genome to analyse Mycobacterium leprae (that causes leprosy), and the closely related species M. haemophilum, that mainly causes ulcerating skin infections and arthritis in persons who are severely immunocompromised, and in children causes cervical and perihilar lymphadenitis. The genes identified in these two species as showing PSS may be those that are partially responsible for virulence and resistance to drugs.

Correlation of over-expression of rv1900c with enhanced survival of M. smegmatis under stress conditions: Modulation of cell surface properties

Mycobacterium tuberculosis has distinct cell wall composition that helps in intracellular survival of bacteria. Rv1900c, a two domain protein, has been grouped in lip gene family. The expression of rv1900c was upregulated under acidic, nutritive and iron stress conditions in M. tuberculosis H37Ra. To investigate the biological effect of Rv1900c in mycobacterium physiology, rv1900c gene was cloned in M. smegmatis, a surrogate host. Its counterpart MSMEG_4477 in M. smegmatis demonstrated 38% protein similarity with Rv1900c. MSMEG_4477 gene was knocked out in M. smegmatis by homologous recombination. rv1900c and MSMEG_4477 genes, cloned in pVV16, were expressed in the M. smegmatis knockout strain (M. smegmatis ΔMSMEG_4477). Gene knockout significantly altered colony morphology and growth kinetics of M. smegmatis. M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) colonies were less wrinkled and had smooth surface as compared to M. smegmatis ΔMSMEG_4477. The changes were reverted back to normal upon expression of MSMEG_4477 in knockout strain M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). The expression of rv1900c enhanced the biofilm formation and survival of bacteria under various in vitro stresses like acidic, nutritive stress, including lysozyme, SDS and multiple antibiotics treatment in comparison to control. On the other hand the expression of rv1900c decreased the cell wall permeability. The resistance provided by M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477) was comparable to M. smegmatis having vector alone (MS_vec). The lipid content of M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) was observed to be different from M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) was more tolerant to stress conditions in comparison to M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). Expression of rv1900c enhanced the intracellular survival of mycobacteria. Therefore, the present study suggested an association of Rv1900c to the stress tolerance by cell wall modification that might have resulted in enhanced intracellular survival of the mycobacteria.

A systemic approach to explore the mechanisms of drug resistance and altered signaling cascades in extensively drug-resistant tuberculosis

BACKGROUND AND AIM

The persistence of extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis (MTB) continue to pose a significant challenge to the treatment and control of tuberculosis infections worldwide. XDR-MTB strains exhibit resistance against first-line anti-TB drugs, fluoroquinolones, and second-line injectable drugs. The mechanisms of drug resistance of MTB remains poorly understood. Our study aims at identifying the differentially expressed genes (DEGs), associated gene networks, and signaling cascades involved in rendering this pathogen resistant to multiple drugs, namely, isoniazid, rifampicin, and capreomycin.

METHODS

We used the microarray dataset GSE53843. The GEO2R tool was used to prioritize the most significant DEGs (top 250) of each drug exposure sample between XDR strains and non-resistant strains. The validation of the 250 DEGs was performed using volcano plots. Protein-protein interaction networks of the DEGs were created using STRING and Cytoscape tools, which helped decipher the relationship between these genes. The significant DEGs were functionally annotated using DAVID and ClueGO. The concomitant biological processes (BP) and molecular functions (MF) were represented as dot plots.

RESULTS AND CONCLUSION

We identified relevant molecular pathways and biological processes, such as cell wall biogenesis, lipid metabolic process, ion transport, phosphopantetheine binding, and triglyceride lipase activity. These processes indicated the involvement of multiple interconnected mechanisms in drug resistance. Our study highlighted the impact of cell wall permeability, with the dysregulation of the mur family of proteins, as essential factors in the inference of resistance. Additionally, upregulation of genes responsible for ion transport such as ctpF, arsC, and nark3, emphasizes the importance of transport channels and efflux pumps in potentially driving out stress-inducing compounds. This study investigated the upregulation of the Lip family of proteins, which play a crucial role in triglyceride lipase activity. Thereby illuminating the potential role of drug-induced dormancy and subsequent resistance in the mycobacterial strains. Multiple mechanisms such as carboxylic acid metabolic process, NAD biosynthetic process, triglyceride lipase activity, phosphopantetheine binding, organic acid biosynthetic process, and growth of symbiont in host cell were observed to partake in resistance of XDR-MTB. This study ultimately provides a platform for important mapping targets for potential therapeutics against XDR-MTB.

Characterization of EstDR4, a Novel Cold-Adapted Insecticides-Metabolizing Esterase from Deinococcus radiodurans

Cold-adapted esterases are attracting increasing attention owing to their prospective use in biotechnology. In this study, a novel cold-adapted family Ⅳ esterase EstDR4 was identified and obtained from extremophile Deinococcus radiodurans (D. radiodurans). EstDR4 displayed significant substrate preference towards short and medium chain monoesters (C2–C12). It also showed regioselectivity, enantioselectivity and degradation effects on four insecticides. The optimum temperature and pH for EstDR4 activity were 30 °C and pH 8, respectively. Additionally, EstDR4 exhibited relatively high catalytic activity at 0 °C and high stability from 10–40 °C, with over 80% of its initial activity retained after 1 h of incubation. Moreover, EstDR4 activity was stimulated by Tween 80 and Triton X-100, and inhibited by metal ions such as Co2+, Cu2+ and Zn2+ and several organic solvents. Thus, this enzyme shows development potential for many industrial biotechnological applications, including the manufacture of thermolabile pharmaceutical products, cold-wash detergents and insecticide biodegradation.

New 2-Ethylthio-4-methylaminoquinazoline derivatives inhibiting two subunits of cytochrome bc1 in Mycobacterium tuberculosis

The emergence of multi-drug (MDR-TB) and extensively-drug resistant tuberculosis (XDR-TB) is a major threat to the global management of tuberculosis (TB) worldwide. New chemical entities are of need to treat drug-resistant TB. In this study, the mode of action of new, potent quinazoline derivatives was investigated against Mycobacterium tuberculosis (M. tb). Four derivatives 11626141, 11626142, 11626252 and 11726148 showed good activity (MIC ranging from 0.02-0.09 μg/mL) and low toxicity (TD50 ≥ 5μg/mL) in vitro against M. tb strain H37Rv and HepG2 cells, respectively. 11626252 was the most selective compound from this series. Quinazoline derivatives were found to target cytochrome bc1 by whole-genome sequencing of mutants selected with 11626142. Two resistant mutants harboured the transversion T943G (Trp312Gly) and the transition G523A (Gly175Ser) in the cytochrome bc1 complex cytochrome b subunit (QcrB). Interestingly, a third mutant QuinR-M1 contained a mutation in the Rieske iron-sulphur protein (QcrA) leading to resistance to quinazoline and other QcrB inhibitors, the first report of cross-resistance involving QcrA. Modelling of both QcrA and QcrB revealed that all three resistance mutations are located in the stigmatellin pocket, as previously observed for other QcrB inhibitors such as Q203, AX-35, and lansoprazole sulfide (LPZs). Further analysis of the mode of action in vitro revealed that 11626252 exposure leads to ATP depletion, a decrease in the oxygen consumption rate and also overexpression of the cytochrome bd oxidase in M. tb. Our findings suggest that quinazoline-derived compounds are a new and attractive chemical entity for M. tb drug development targeting two separate subunits of the cytochrome bc1 complex.

Biochemical characterization of an esterase from Clostridium acetobutylicum with novel GYSMG pentapeptide motif at the catalytic domain

Gene CA_C0816 codes for a serine hydrolase protein from Clostridium acetobutylicum (ATCC 824) a member of hormone-sensitive lipase of lipolytic family IV. This gene was overexpressed in E. coli strain BL21and purified using Ni²⁺-NTA affinity chromatography. Size exclusion chromatography revealed that the protein is a dimer in solution. Optimum pH and temperature for recombinant Clostridium acetobutylicum esterase (Ca-Est) were found to be 7.0 and 60 °C, respectively. This enzyme exhibited high preference for p-nitrophenyl butyrate. K_M and k_cat/K_M of the enzyme were 24.90 µM and 25.13 s^-1 µM^-1, respectively. Sequence analysis of Ca-Est predicts the presence of catalytic amino acids Ser 89, His 224, and Glu 196, presence of novel GYSMG conserved sequence (instead of GDSAG and GTSAG motif), and undescribed variation of HGSG motif. Site-directed mutagenesis confirmed that Ser 89 and His 224 play a major role in catalysis. This study reports that Ca-Est is hormone-sensitive lipase with novel GYSMG pentapeptide motif at a catalytic domain.

Lipid metabolism and intracellular bacterial virulence: key to next-generation therapeutics

Lipid metabolism is thought to play a key role in the pathogenicity of several intracellular bacteria. Bacterial lipolytic enzymes hydrolyze lipids from the host cell to release free fatty acids which are used as an energy source and building blocks for the synthesis of cell envelope and also to modulate host immune responses. In this review, we discussed the role of lipid metabolism and lipolytic enzymes in the life cycle and virulence of Mycobacterium tuberculosis and other intracellular bacteria. The lipolytic enzymes appear to be potential candidates for developing novel therapeutics by targeting lipid metabolism for controlling M. tuberculosis and other intracellular pathogenic bacteria.

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Drug targeted virtual screening and molecular dynamics of LipU protein of Mycobacterium tuberculosis and Mycobacterium leprae

The lipolytic protein LipU was conserved in mycobacterium sp. including M. tuberculosis (MTB LipU) and M. leprae (MLP LipU). The MTB LipU was identified in extracellular fraction and was reported to be essential for the survival of mycobacterium. Therefore to address the problem of drug resistance in pathogen, LipU was selected as a drug target and the viability of finding out some FDA approved drugs as LipU inhibitors in both the cases was explored. Three-dimensional (3D) model structures of MTB LipU and MLP LipU were generated and stabilized through molecular dynamics (MD). FDA approved drugs were screened against these proteins. The result showed that the top-scoring compounds for MTB LipU were Diosmin, Acarbose and Ouabain with the Glide XP score of -12.8, -11.9 and -11.7 kcal/mol, respectively, whereas for MLP LipU protein, Digoxin (-9.2 kcal/mol), Indinavir (-8.2 kcal/mol) and Travoprost (-8.2 kcal/mol) showed highest affinity. These drugs remained bound in the active site pocket of MTB LipU and MLP LipU structure and interaction grew stronger after dynamics. RMSD, RMSF and Rg were found to be persistent throughout the simulation period. Hydrogen bonds along with large number of hydrophobic interactions stabilized the complex structures. Binding free energies obtained through Prime/MM-GBSA were found in the significant range from -63.85 kcal/mol to -34.57 kcal/mol for MTB LipU and -71.33 kcal/mol to -23.91 kcal/mol for MLP LipU. The report suggested high probability of these drugs to demolish the LipU activity and could be probable drug candidates to combat TB and leprosy disease.

Investigations into Isoniazid Treated Mycobacterium tuberculosis by Electrospray Mass Spectrometry Reveals New Insights into Its Lipid Composition

Many of the earlier studies involving the effect of isoniazid (INH) treatment have solely focused on the fatty acyl (FA) category of Mycobacterium tuberculosis (MTB) lipids. This motivated us with the major interest to examine the impact of INH on various other categories of MTB lipids. Towards this, we chose to interpret our mass spectral data (LC-ESI-MS) by a standalone software, MS-LAMP, in which "Mtb LipidDB" was integrated. Analysis by MS-LAMP revealed that INH treatment can alter the composition of "glycerolipids (GLs)" and "glycerophospholipids (GPLs)" categories of MTB lipids, in addition to the variations to FA category. Interpretation by "MycoMass" database yielded similar results as that of Mtb LipidDB, except that significant alterations to polyketides (PKs) category also were observed. Probing biosynthetic pathways of certain key lipids belonging to any of GLs, GPLs, and PKs categories can be attractive target(s) for drug discovery or can be useful to identify means to overcome drug resistance or to obtain insights into the causal factors of virulence. To the best of our knowledge, this is the first report hinting at the influence of INH on GLs, GPLs, and PKs of MTB.

Impact of signal peptide and transmembrane segments on expression and biochemical properties of a lipase from Bacillus sphaericus 205y

A total of 97 amino acids, considered as the signal peptide and transmembrane segments were removed from 205y lipase gene using polymerase chain reaction technique that abolished the low activity of this enzyme. The mature enzyme was expressed in Escherichia coli using pBAD expression vector, which gave up to a 13-fold increase in lipase activity. The mature 205y lipase (without signal peptide and transmembrane; -SP/TM) was purified to homogeneity using the isoelectric focusing technique with 53% recovery. Removing of the signal peptide and transmembrane segments had resulted in the shift of optimal pH, an increase in optimal temperature and tolerance towards more water-miscible organic solvents as compared to the characteristics of open reading frame (ORF) of 205y lipase. Also, in the presence of 1mM inhibitors, less decrease in the activity of mature 205y lipase was observed compared to the ORF of the enzyme. Protein structure modeling showed that 205y lipase consisted of an α/β hydrolase fold without lid domain. However, the transmembrane segment could effect on the enzyme activity by covering the active site or aggregation the protein.

A pipeline for proteome-scale identification and studies on hormone sensitive lipases in Mycobacterium tuberculosis

Hormone sensitive lipases (HSLs) play an important role in the survival of M. tuberculosis during dormancy. They help in the utilization of fatty acids from stored lipids. The objective of the current study was to identify all HSLs from the proteome of M. tuberculosis H37Rv. We have developed a novel HSL identification pipeline, based on amino acid sequence homology, presence of conserved motifs and other sequence features deciphered from known HSL dataset. Through this pipeline, we identified 10 proteins as putative HSLs in M. tuberculosis. We have annotated a lipase LipT, as putative p-nitrobenzyl esterase and also identified a new motif "PGG" which is a possible characteristic motif of a subfamily of HSLs.