Characterization of LipN (Rv2970c) of Mycobacterium Tuberculosis H37Rv and its Probable Role in Xenobiotic Degradation

A conserved but structurally divergent loop in acyl protein thioesterase 1 regulates its catalytic activity, ligand binding, and folded stability

Human acyl protein thioesterases (APTs) catalyze the depalmitoylation of S-acylated proteins attached to the plasma membrane, facilitating reversible cycles of membrane anchoring and detachment. We previously showed that a bacterial APT homologue, FTT258 from the gram-negative pathogen Francisella tularensis, exists in equilibrium between a closed and open state based on the structural dynamics of a flexible loop overlapping its active site. Although the structural dynamics of this loop are not conserved in human APTs, the amino acid sequence of this loop is highly conserved, indicating essential but divergent functions for this loop in human APTs. Herein, we investigated the role of this loop in regulating the catalytic activity, ligand binding, and protein folding of human APT1, a depalmitoylase connected with cancer, immune, and neurological signaling. Using a combination of substitutional analysis with kinetic, structural, and biophysical characterization, we show that even in its divergent structural location in human APT1 that this loop still regulates the catalytic activity of APT1 through contributions to ligand binding and substrate positioning. We confirmed previously known roles for multiple residues (Phe72 and Ile74) in substrate binding and catalysis while adding new roles in substrate selectivity (Pro69), in catalytic stabilization (Asp73 and Ile75), and in transitioning between the membrane binding β-tongue and substrate-binding loops (Trp71). Even conservative substitution of this tryptophan (Trp71) fulcrum led to complete loss of catalytic activity, a 13°C decrease in total protein stability, and drastic drops in ligand affinity, indicating that the combination of the size, shape, and aromaticity of Trp71 are essential to the proper structure of APT1. Mixing buried hydrophobic surface area with contributions to an exposed secondary surface pocket, Trp71 represents a previously unidentified class of essential tryptophans within α/β hydrolase structure and a potential allosteric binding site within human APTs.

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.

Sequence and Structural Motifs Controlling the Broad Substrate Specificity of the Mycobacterial Hormone-Sensitive Lipase LipN

Mycobacterium tuberculosis has a complex life cycle transitioning between active and dormant growth states depending on environmental conditions. LipN (Rv2970c) is a conserved mycobacterial serine hydrolase with regulated catalytic activity at the interface between active and dormant growth conditions. LipN also catalyzes the xenobiotic degradation of a tertiary ester substrate and contains multiple conserved motifs connected with the ability to catalyze the hydrolysis of difficult tertiary ester substrates. Herein, we expanded a library of fluorogenic ester substrates to include more tertiary and constrained esters and screened 33 fluorogenic substrates for activation by LipN, identifying its unique substrate signature. LipN preferred short, unbranched ester substrates, but had its second highest activity against a heteroaromatic five-membered oxazole ester. Oxazole esters are present in multiple mycobacterial serine hydrolase inhibitors but have not been tested widely as ester substrates. Combined structural modeling, kinetic measurements, and substitutional analysis of LipN showcased a fairly rigid binding pocket preorganized for catalysis of short ester substrates. Substitution of diverse amino acids across the binding pocket significantly impacted the folded stability and catalytic activity of LipN with two conserved motifs (HGGGW and GDSAG) playing interconnected, multidimensional roles in regulating its substrate specificity. Together this detailed substrate specificity profile of LipN illustrates the complex interplay between structure and function in mycobacterial hormone-sensitive lipase homologues and indicates oxazole esters as promising inhibitor and substrate scaffolds for mycobacterial hydrolases.

Identification of Tregs-Related Genes with Molecular Patterns in Patients with Systemic Sclerosis Related to ILD

Background: Systemic Sclerosis (SSc) is an autoimmune disease that is characterized by vasculopathy, digital ulcers, Raynaud’s phenomenon, renal failure, pulmonary arterial hypertension, and fibrosis. Regulatory T (Treg) cell subsets have recently been found to play crucial roles in SSc with interstitial lung disease (ILD) pathogenesis. This study investigates the molecular mechanism of Treg-related genes in SSc patients through bioinformatic analyses. Methods: The GSE181228 dataset of SSc was used in this study. CIBERSORT was used for assessing the category and proportions of immune cells in SSc. Random forest and least absolute shrinkage and selection operator (LASSO) regression analysis were used to select the hub Treg-related genes. Results: Through bioinformatic analyses, LIPN and CLEC4D were selected as hub Treg-regulated genes. The diagnostic power of the two genes separately for SSc was 0.824 and 0.826. LIPN was associated with the pathway of aminoacyl−tRNA biosynthesis, Primary immunodeficiency, DNA replication, etc. The expression of CLEC4D was associated with the pathway of Neutrophil extracellular trap formation, PPAR signaling pathway, Staphylococcus aureus infection, Systemic lupus erythematosus, TNF signaling pathway, and Toll−like receptor signaling pathway. Conclusion: Through bioinformatic analyses, we identified two Treg-related hub genes (LIPN, CLEC4D) that are mainly involved in the immune response and metabolism of Tregs in SSc with ILD. Moreover, our findings may provide the potential for studying the molecular mechanism of SSc with ILD.

Mechanism of visible light enhances microbial degradation of Bisphenol A

Bisphenol A (BPA) is a toxic endocrine disruptor detected in various environments. Microbial metabolic/enzymatic degradation has been thought to be the main pathway for BPA attenuation in natural environments. In this study, we found that under visible light conditions, superoxide produced by bacteria was the main reason for the rapid removal of BPA, accounting for 57 % of the total removal rate. With visible light, the bacteria degraded BPA at a rate of 0.22 mg/L/d, and the total removal within 8 days reached 85 %, which is 4.7 times compared with that of dark culture. The intermediate product 4-iso-propenylphenol, which was considered as an end-product of microbial degradation of BPA in previous reports, was detected in large quantities at 24 h in culture but gradually decreased in our experiment. Community analysis suggested bacteria with aromatic hydrocarbon degradation ability were more enriched under light incubation. Moreover, the bacteria showed well degradation ability to various pharmaceutically active but nonbiodegradable compounds including diclofenac and fluoxetine, with a removal rate of 88 % and 20 %, respectively. Our study revealed the organic pollutant transformation pathway under the combined action of light and microorganisms, providing new insights into the microbial treatment of aromatic hydrocarbon pollutants.

Environment dependent expression of mycobacterium hormone sensitive lipases: expression pattern under ex-vivo and individual in-vitro stress conditions in M. tuberculosis H37Ra

BACKGROUND

Hormone-sensitive lipase (HSL) is a neutral lipase capable of hydrolysing various kinds of lipids. In comparison to single human Hormone Sensitive Lipase (hHSL), that is induced under nutritional stress, twelve serine hydrolases are annotated as HSL in Mycobacterium tuberculosis (mHSL). Mycobacterium is exposed to multiple stresses inside the host. Therefore, the present study was carried out to investigate if mHSL are also expressed under stress condition and if there is any correlation between various stress conditions and expression pattern of mHSL.

METHODS AND RESULTS

The expression pattern of mHSL under different environmental conditions (in-vitro and ex-vivo) were studied using qRT-PCR in M. tuberculosis H37Ra strain with 16 S rRNA as internal control. Out of 12, only two genes (lipU and lipY) were expressed at very low level in mid log phase culture under aerobic conditions, while 9 genes were expressed at stationary phase of growth. Ten mHSLs were expressed post-infection under ex-vivo conditions in time dependent manner. LipH and lipQ did not express at any time point under ex-vivo condition. The relative expression of most of the genes under individual stress was much higher than observed in ex-vivo conditions. The expression pattern of genes varied with change in stress condition.

CONCLUSIONS

Different sets of mHSL genes were expressed under different individual stress conditions pointing towards the requirement of different mHSL to combat different stress conditions. Overall, most of the mHSLs have demonstrated stress dependent expression pointing towards their role in intracellular survival of mycobacteria.

Identification of Optimal Expression Parameters and Purification of a Codon-Optimized Human GLIS1 Transcription Factor from Escherichia coli

GLIS1 has multiple roles in embryonic development and in deriving induced pluripotent stem cells by aiding signaling pathways and chromatin assembly. An inexpensive and simple method to produce human GLIS1 protein from Escherichia coli (E. coli) is demonstrated in this study. Various parameters such as codon usage bias, E. coli strains, media, induction conditions (such as inducer concentration, cell density, time, and temperature), and genetic constructs were investigated to obtain soluble expression of human GLIS1 protein. Using identified expression conditions and an appropriate genetic construct, the human GLIS1 protein was homogeneously purified (purity > 90%) under native conditions. Importantly, the purified protein has upheld a stable secondary structure, as demonstrated by circular dichroism spectroscopy. To the best of our knowledge, this is the first study to report the ideal expression conditions of human GLIS1 protein in E. coli to achieve soluble expression and purification under native conditions, upholding its stable secondary structure post-purification. The biological activity of the purified GLIS1 fusion protein was further assessed in MDA-MB-231 cells. This biologically active human GLIS1 protein potentiates new avenues to understand its molecular mechanisms in different cellular functions in various cancers and in the generation of induced pluripotent stem cells.

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.

The lipolytic activity of LipJ, a stress-induced enzyme, is regulated by its C-terminal adenylate cyclase domain

Aim: The confirmation of lipolytic activity and role of Rv1900c in the Mycobacterium physiology Methods: rv1900c/N-terminus domain (rv1900NT) were cloned in pET28a/Escherichia coli, purified by affinity chromatography and characterized. Results: A zone of clearance on tributyrin-agar and activity with pNP-decanoate confirmed the lipolytic activity of Rv1900c. The Rv1900NT demonstrated higher enzyme specific activity, V_max and k_cat, but Rv1900c was more thermostable. The lipolytic activity of Rv1900c decreased in presence of ATP. Mycobacterium smegmatis expressed rv1900c/rv1900NT-altered colony morphology, growth, cell surface properties and survival under stress conditions. The effect was more prominent with Rv1900NT as compared with Rv1900c. Conclusion: The study confirmed the lipolytic activity of Rv1900c and suggested its regulation by the adenylate cyclase domain and role in the intracellular survival of bacteria.

Hormone-sensitive lipase: sixty years later

Hormone-sensitive lipase (HSL) was initially characterized as the hormonally regulated neutral lipase activity responsible for the breakdown of triacylglycerols into fatty acids in adipose tissue. This review aims at providing up-to-date information on structural properties, regulation of expression, activity and function as well as therapeutic potential. The lipase is expressed as different isoforms produced from tissue-specific alternative promoters. All isoforms are composed of an N-terminal domain and a C-terminal catalytic domain within which a regulatory domain containing the phosphorylation sites is embedded. Some isoforms possess additional N-terminal regions. The catalytic domain shares similarities with bacteria, fungus and vascular plant proteins but not with other mammalian lipases. HSL singularity is provided by regulatory and N-terminal domains sharing no homology with other proteins. HSL has a broad substrate specificity compared to other neutral lipases. It hydrolyzes acylglycerols, cholesteryl and retinyl esters among other substrates. A novel role of HSL, independent of its enzymatic function, has recently been described in adipocytes. Clinical studies revealed dysregulations of HSL expression and activity in disorders, such as lipodystrophy, obesity, type 2 diabetes and cancer-associated cachexia. Development of specific inhibitors positions HSL as a pharmacological target for the treatment of metabolic complications.

A novel carboxylesterase from Acinetobacter sp. JNU9335 for efficient biosynthesis of Edoxaban precursor with high substrate to catalyst ratio

A novel carboxylesterase AcEst1 was identified from Acinetobacter sp. JNU9335 with high efficiency in the biosynthesis of chiral precursor of Edoxaban through kinetic resolution of methyl 3-cyclohexene-1-carboxylate (CHCM). Sequence analysis revealed AcEst1 belongs to family IV of esterolytic enzymes and exhibits <40% identities with known carboxylesterases. The optimum pH and temperature of recombinant AcEst1 are 8.0 and 40 °C. Substrate spectrum analysis indicated that AcEst1 prefers substrates with short acyl and alcohol groups. AcEst1 was highly active in the hydrolysis of CHCM with k_cat of 1153 s^-1 and displayed high substrate tolerance. As much as 2.0 M (280 g·L^-1) CHCM could be enantioselectively hydrolyzed into (S)-CHCM by merely 0.08 g·L^-1AcEst1 with ee_s of >99% (S) and substrate to catalyst ratio (S/C) of 3500 g·g^-1. These results indicate that the novel AcEst1 is a promising biocatalyst in the synthesis of chiral carboxylic acids.

Mycobacterium tuberculosis LipE Has a Lipase/Esterase Activity and Is Important for Intracellular Growth and In Vivo Infection

Mycobacterium tuberculosis Rv3775 (LipE) was annotated as a putative lipase. However, its lipase activity has never been characterized, and its precise role in tuberculosis (TB) pathogenesis has not been thoroughly studied to date. We overexpressed and purified the recombinant LipE (rLipE) protein and demonstrated that LipE has a lipase/esterase activity. rLipE prefers medium-chain ester substrates, with the maximal activity on hexanoate. Its activity is the highest at 40°C and pH 9. We determined that rLipE hydrolyzes trioctanoate. Using site-directed mutagenesis, we confirmed that the predicted putative activity triad residues Ser97, Gly342, and His363 are essential for the lipase activity of rLipE. The expression of the lipE gene was induced under stressed conditions mimicking M. tuberculosis' intracellular niche. The gene-disrupting mutation of lipE led to significantly reduced bacterial growth inside THP-1 cells and human peripheral blood mononuclear cell-derived macrophages and attenuated M. tuberculosis infection in mice (with ∼8-fold bacterial load reduction in mouse lungs). Our data suggest that LipE functions as a lipase and is important for M. tuberculosis intracellular growth and in vivo infection.

Rv2223c, an acid inducible carboxyl-esterase of Mycobacterium tuberculosis enhanced the growth and survival of Mycobacterium smegmatis

Aim: To elucidate the role of Rv2223c in Mycobacterium tuberculosis. Methods: Purified recombinant Rv2223c protein was characterized. Expression of rv2223c in the presence of different stress environment and subcellular localization were performed in M. tuberculosis H37Ra and Mycobacterium smegmatis ( MS_2223c). Effect of its overexpression on growth rate, infection and intracellular survival in THP-1/PBMC cells were studied. Results: rRv2223c demonstrated esterase activity with preference for pNP-octanoate and hydrolyzed trioctanoate to di- and mono-octanoate. Expression of rv2223c was upregulated in acidic and nutritive stress conditions. rRv2223c was identified in extracellular and cell wall fractions. MS_2223c exhibited enhanced growth, survival during in vitro stress, infection and intracellular survival. Conclusions: Rv2223c is a secretary, carboxyl-esterase, with enhanced expression under acidic and nutritive stress condition and might help in intracellular survival of bacteria.

Molecular characterization and immunogenic function of ML1899 (LipG) of Mycobacterium leprae

Introduction. ML1899 is conserved in all mycobacterium sp. and is a middle member of mle-ML1898 operon involved in mycolic acid modification.Aim. In the present study attempts were made to characterize ML1899 in detail.Methodology. Bioinformatics tools were used for prediction of active-site residues, antigenic epitopes and a three-dimensional model of protein. The gene was cloned, expressed and purified as His-tagged protein in Escherichia coli for biophysical/biochemical characterization. Recombinant protein was used to treat THP-1 cells to study change in production of nitric oxide (NO), reactive oxygen species (ROS), cytokines and chemokines using flowcytometry/ELISA.Results. In silico analysis predicted ML1899 as a member of α/β hydrolase family with GXSXG-motif and Ser126, His282, Asp254 as active-site residues that were confirmed by site-directed mutagensis. ML1899 exhibited esterase activity. It hydrolysed pNP-butyrate as optimum substrate at pH 8.0 and 50 °C with 5.56 µM^-1 min^-1 catalytic efficiency. The enzyme exhibited stability up to 60 °C temperature and between pH 6.0 to 9.0. K _m, V _max and specific activity of ML1899 were calculated to be 400 µM, 40 µmoles min^-1 ml^-1 and 27 U mg^{- 1}, respectively. ML1899 also exhibited phospholipase activity. The protein affected the survival of macrophages when treated at higher concentration. ML1899 enhanced ROS/NO production and up-regulated pro-inflammatory cytokines and chemokine including TNF-α, IFN-γ, IL-6 and IL-8 in macrophages. ML1899 was also observed to elicit humoral response in 69 % of leprosy patients.Conclusion. These results suggested that ML1899, an esterase could up-regulate the immune responses in favour of macrophages at a low concentration but kills the THP-1 macrophages cells at a higher concentration.

Rv1075c of Mycobacterium tuberculosis is a GDSL-Like Esterase and Is Important for Intracellular Survival

Mycobacterium tuberculosis lipid metabolism pathways facilitate access to carbon and energy sources during infection. M. tuberculosis gene Rv1075c was annotated as a conserved hypothetical protein. We identified that Rv1075c amino acid sequence shares similarities with other bacterial lipase/esterases and we demonstrated that it has esterase activity, with preference for short-chain fatty acids, particularly acetate, with highest activity at 45°C, pH 9. Site-direct mutagenesis revealed its activity triad as Ser80, Asp244, and His247. We further determined that rRv1075c hydrolyzed triacetin and tributyrin, and it was mainly distributed in cell wall and membrane. Its expression was induced at pH 4.5, mimicking the acidic phagosome of macrophages. Mutation of Rv1075c led to reduced bacterial growth in THP-1 cells and human peripheral blood mononuclear cell-derived macrophages, and attenuated M. tuberculosis infection in mice. Our data suggest that Rv1075c is involved in ester and fatty acid metabolism inside host cells.

Rv1288, a Two Domain, Cell Wall Anchored, Nutrient Stress Inducible Carboxyl-Esterase of Mycobacterium tuberculosis, Modulates Cell Wall Lipid

Rv1288, a conserved hypothetical protein of M. tuberculosis (M.tb), was recently characterized as two-domain esterase enzyme by in silico study. In the present study, Rv1288 and its domains (Est and Lyt) were cloned individually from M.tb into E. coli for expression and purification. The purified rRv1288 and rEst proteins exhibited lipolytic activity with medium chain length esters as optimum substrates, while Lyt domain did not show enzymatic activity. However, presence of Lyt domain resulted in enhanced rate of protein aggregation at higher temperature. Both rRv1288 and rEst followed the similar patterns of substrate specificity, temperature and pH activity. Site directed mutagenesis confirmed the Ser-294, Asp-391 and His-425 as catalytic site residues. Rv1288 was found to be present in cell wall fraction of M.tb H37Ra. Peptidoglycan binding activity of Rv1288 and its domains demonstrated that the Lyt domain is essential for anchoring protein to the cell wall. Expression of rv1288 was up regulated in M.tb under nutrient starved condition. Over expression of rv1288 in surrogate host M. smegmatis led to change in colony morphology, enhanced pellicle and aggregate formation that might be linked with the changed lipid composition of bacterial cell wall. Cell wall of M. smegmatis expressing rv1288 had higher amount of lipids, with a significant increase in trehalose dimycolate content. Rv1288 also leads to increase in drug resistance of M. smegmatis. Rv1288 also enhanced the intracellular survival of M. smegmatis in Raw264.7 cell line. Overall, this study suggested that Rv1288, a cell wall localized carboxyl hydrolase with mycolyl-transferase activity, modulated the cell wall lipids to favor the survival of bacteria under stress condition.

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.

[Formula: see text]

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.

mbtJ: an iron stress-induced acetyl hydrolase/esterase of Mycobacterium tuberculosis helps bacteria to survive during iron stress

AIM

mbtJ from Mycobacterium tuberculosis H37Rv is a member of mbt A-J operon required for mycobactin biogenesis.

MATERIALS & METHODS

The esterase/acetyl-hydrolase activity of mbtJ was determined by pNP-esters/native-PAGE and expression under iron stress by quantitative-PCR. Effect of gene on growth/survival of Mycobacterium was studied using antisense. Its effect on morphology, growth/infection was studied in Mycobacterium smegmatis.

RESULTS

It showed acetyl hydrolase/esterase activity at pH 8.0 and 50°C with pNP-butyrate. Its expression was upregulated under iron stress. The antisense inhibited the survival of bacterium during iron stress. Expression of mbtJ changed colony morphology and enhanced the growth/infection in M. smegmatis.

CONCLUSION

mbtJ, an acetyl-hydrolase/esterase, enhanced the survival of M. tuberculosis under iron stress, affected the growth/infection efficiency in M. smegmatis, suggesting its pivotal role in the intracellular survival of bacterium.

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.

Structural and functional insights into thermostable and organic solvent stable variant Pro247-Ser of Bacillus lipase

Thermostability of enzymes is an important issue in protein engineering and has been studied in detail. Still there is no hard and fast rule to define the conditions which will provide thermal stability. Understanding the various factors and mechanism responsible for thermal stability will add on new insights into our present knowledge in this area. Pro247-Ser variant was constructed based on homology modelling and rational design. It exhibited 60 fold increase in thermal stability at 60°C and+0.7M shift in C_1/2 value for urea denaturation as compared to WT. Variant displayed noticeable tolerance to organic solvents. With decrease in K_m, catalytic efficiency of Pro247-Ser variant was increased by 12 fold. The activity and stability assay including circular dichroism and fluorescence spectroscopy favoured increased thermal performance of variant. Hydrolytic activity of variant was found to be high in comparison to control for all p-nitrophenol esters investigated. The immobilized variant enzyme demonstrated nearly two fold enhanced conversion of methyl oleate than WT enzyme. The additional molecular interactions of variant residue might contribute to increased thermostability of lipase. The homology modeling predicted formation of additional hydrogen bonds between Ser247/O-Thr251/OG1 as well as Ser247/O-Glu250/N.

Cyclipostins and Cyclophostin analogs as promising compounds in the fight against tuberculosis

A new class of Cyclophostin and Cyclipostins (CyC) analogs have been investigated against Mycobacterium tuberculosis H37Rv (M. tb) grown either in broth medium or inside macrophages. Our compounds displayed a diversity of action by acting either on extracellular M. tb bacterial growth only, or both intracellularly on infected macrophages as well as extracellularly on bacterial growth with very low toxicity towards host macrophages. Among the eight potential CyCs identified, CyC₁₇ exhibited the best extracellular antitubercular activity (MIC₅₀ = 500 nM). This compound was selected and further used in a competitive labelling/enrichment assay against the activity-based probe Desthiobiotin-FP in order to identify its putative target(s). This approach, combined with mass spectrometry, identified 23 potential candidates, most of them being serine or cysteine enzymes involved in M. tb lipid metabolism and/or in cell wall biosynthesis. Among them, Ag85A, CaeA and HsaD, have previously been reported as essential for in vitro growth of M. tb and/or survival and persistence in macrophages. Overall, our findings support the assumption that CyC₁₇ may thus represent a novel class of multi-target inhibitor leading to the arrest of M. tb growth through a cumulative inhibition of a large number of Ser- and Cys-containing enzymes participating in important physiological processes.

mesT, a unique epoxide hydrolase, is essential for optimal growth of Mycobacterium tuberculosis in the presence of styrene oxide

Aim: mesT of Mycobacterium tuberculosis, a hypothetical/putative epoxide hydrolase, is predicted to convert toxic epoxides to the more water-soluble and less toxic diols. Detailed characterization of the protein was carried out. Results: mesT demonstrated esterase as well as epoxide hydrolase activity. It was membrane bound and was upregulated under hypoxic conditions. The enzyme was able to degrade styrene oxide. The presence of antisense against this gene resulted in the inhibition of in vitro bacterial growth/survival in the presence of styrene oxide. Conclusion & future perspective: We demonstrated that mesT possessed epoxide hydrolase activity and styrene oxide might be its physiological substrate. Inhibition of mesT reduced the growth of the bacteria in presence of styrene oxide and its expression under hypoxic condition suggested its role in intracellular survival of bacteria.

Multifaceted role of lipids in Mycobacterium leprae

Mycobacterium leprae must adopt a metabolic strategy and undergo various metabolic alterations upon infection to survive inside the human body for years in a dormant state. A change in lipid homeostasis upon infection is highly pronounced in Mycobacterium leprae. Lipids play an essential role in the survival and pathogenesis of mycobacteria. Lipids are present in several forms and serve multiple roles from being a source of nutrition, providing rigidity, evading the host immune response to serving as virulence factors, etc. The synthesis and degradation of lipids is a highly regulated process and is the key to future drug designing and diagnosis for mycobacteria. In the current review, an account of the distinct roles served by lipids, the mechanism of their synthesis and degradation has been elucidated.

Rv0774c, an iron stress inducible, extracellular esterase is involved in immune-suppression associated with altered cytokine and TLR2 expression

Tuberculosis, one of the leading cause of death from infectious diseases, is caused by Mycobacterium tuberculosis. The genome of M. tuberculosis has been sequenced and nearly 40% of the whole genome sequence was categorized as hypothetical. Rv0774c was annotated as membrane exported hypothetical protein in TB database. In silico analysis revealed that Rv0774c is a paralog of PE-PGRS multi gene family with 100 aa N-terminal domain similar to PE domain of PE-PGRS proteins. Its C-terminal domain is quite different from PGRS domain, having characteristic lipase signature GXSXG & HG and catalytic residues predicted for lipolytic activity. Therefore, DNA coding for Rv0774c (303 aa), its N-terminal (1-100 aa) and C- terminal domain (100-303 aa) were separately cloned from M. tuberculosis and were over expressed in E. coli. Rv0774c gene and its C-terminal lipolytic domain preferably hydrolyzed short chain esters. Though no enzyme activity was observed in N-terminus PE like domain, it was demonstrated to enhance the thermostability of full length Rv0774c. Tetrahydrolipstatin inhibited the enzyme activity and predicted catalytic residues (Ser-185, Asp-255 and His-281) were confirmed by site directed mutagenesis. Rv0774c was secreted out in culture media by M. tuberculosis and was up-regulated in iron limiting conditions. Treatment of THP-1 cells with rRv0774c resulted in a decline in the LPS induced production of NO and expression of iNOS. rRv0774c treated THP-1 cells also showed an enhanced expression of IL-10 and TLR2. On contrary, it suppressed the LPS induced production of IL-12, chemokines MCP-1 and IL-8. Rv0774c inhibited the LPS induced phosphorylation of p38. These observations suggested that Rv0774c could modulate the pro-inflammatory immune response to support intracellular survival of the mycobacterium.

Structural Basis for the Strict Substrate Selectivity of the Mycobacterial Hydrolase LipW

The complex life cycle of Mycobacterium tuberculosis requires diverse energy mobilization and utilization strategies facilitated by a battery of lipid metabolism enzymes. Among lipid metabolism enzymes, the Lip family of mycobacterial serine hydrolases is essential to lipid scavenging, metabolic cycles, and reactivation from dormancy. On the basis of the homologous rescue strategy for mycobacterial drug targets, we have characterized the three-dimensional structure of full length LipW from Mycobacterium marinum, the first structure of a catalytically active Lip family member. LipW contains a deep, expansive substrate-binding pocket with only a narrow, restrictive active site, suggesting tight substrate selectivity for short, unbranched esters. Structural alignment reinforced this strict substrate selectivity of LipW, as the binding pocket of LipW aligned most closely with the bacterial acyl esterase superfamily. Detailed kinetic analysis of two different LipW homologues confirmed this strict substrate selectivity, as each homologue selected for unbranched propionyl ester substrates, irrespective of the alcohol portion of the ester. Using comprehensive substitutional analysis across the binding pocket, the strict substrate selectivity of LipW for propionyl esters was assigned to a narrow funnel in the acyl-binding pocket capped by a key hydrophobic valine residue. The polar, negatively charged alcohol-binding pocket also contributed to substrate orientation and stabilization of rotameric states in the catalytic serine. Together, the structural, enzymatic, and substitutional analyses of LipW provide a connection between the structure and metabolic properties of a Lip family hydrolase that refines its biological function in active and dormant tuberculosis infection.