Optimizing of a protein extraction method for Mycobacterium tuberculosis proteome analysis using mass spectrometry

Loss of allosteric regulation in α-isopropylmalate synthase identified as an antimicrobial resistance mechanism

Despite our best efforts to discover new antimicrobials, bacteria have evolved mechanisms to become resistant. Resistance to antimicrobials can be attributed to innate, inducible, and acquired mechanisms. Mycobacterium abscessus is one of the most antimicrobial resistant bacteria and is known to cause chronic pulmonary infections within the cystic fibrosis community. Previously, we identified epetraborole as an inhibitor against M. abscessus with in vitro and in vivo activities and that the efficacy of epetraborole could be improved with the combination of the non-proteinogenic amino acid norvaline. Norvaline demonstrated activity against the M. abscessus epetraborole resistant mutants thus, limiting resistance to epetraborole in wild-type populations. Here we show M. abscessus mutants with resistance to epetraborole can acquire resistance to norvaline in a leucyl-tRNA synthetase (LeuRS) editing-independent manner. After showing that the membrane hydrophobicity and efflux activity are not linked to norvaline resistance, whole-genome sequencing identified a mutation in the allosteric regulatory domain of α-isopropylmalate synthase (α-IPMS). We found that mutants with the α-IPMSA555V variant incorporated less norvaline in the proteome and produced more leucine than the parental strain. Furthermore, we found that leucine can rescue growth inhibition from norvaline challenge in the parental strain. Our results demonstrate that M. abscessus can modulate its metabolism through mutations in an allosteric regulatory site to upregulate the biosynthesis of the natural LeuRS substrate and outcompete norvaline. These findings emphasize the antimicrobial resistant nature of M. abscessus and describe a unique mechanism of substrate-inhibitor competition.

Unraveling Potential Candidate Targets Associated with Expression of p16INK4a or p16 Truncated Fragment by Comparative Proteomics Analysis

Background:

p16 is a tumor suppressor protein that is significantly involved in cycle regulation through the reduction of cell progression from the G1 phase to the S phase via CDK-cyclin D/p16INK4a/pRb/E2F cascade. The minimum functional domain of p16 has been uncovered that may function comparable to wild type p16.

Objective:

To expand the knowledge on molecules and mechanisms by which p16 or p1666-156 fragment suppresses human fibrosarcoma cell line growth, differential proteome profiles of fibrosarcoma cells following p16 full length or the functional domain overexpression, were analyzed.

Methods:

Following transfecting HT-1080 fibrosarcoma cells with p16 full length, p1666-156 truncated form, and pcDNA3.1 empty vector, protein extract of each sample was harvested and clarified by centrifugation, and then the protein content was determined via Bradford assay. All protein extract of each sample was analyzed by two-dimensional gel electrophoresis. Immunoblot analysis was performed as further validation of the expression status of identified proteins.

Results:

Expression of p16 or p1666-156 fragment could induce mostly the common alterations (up/- down-regulation) of proteome profile of HT-1080 cells. Mass spectrometry identification of the differentially expressed protein spots revealed several proteins that were grouped in functional clusters, including cell cycle regulation and proliferation, cell migration and structure, oxidative stress, protein metabolism, epigenetic regulation, and signal transduction.

Conclusion:

The minimum functional domain of p16 could act in the same way as p16 full length. Also, these new findings can significantly enrich the understanding of p16 growth-suppressive function at the molecular level by the introduction of potential candidate targets for new treatment strategies. Furthermore, the present study provides strong evidence on the functional efficacy of the identified fragment of p16 for further attempts toward peptidomimetic drug design or gene transfer to block cancer cell proliferation.

Biosafety and Proteome Profiles of Different Heat Inactivation Methods for Mycobacterium tuberculosis

Studies involving the pathogenic organism Mycobacterium tuberculosis routinely require advanced biosafety laboratory facilities, which might not be readily available in rural areas where tuberculosis burdens are high. Attempts to adapt heat inactivation techniques have led to inconsistent conclusions, and the risk of protein denaturation due to extensive heating is impractical for subsequent mass spectrometry (MS)-based protein analyses. In this study, 240 specimens with one or two loops of M. tuberculosis strain H37Rv biomass and specific inactivated solutions were proportionally assigned to six heat inactivation methods in a thermal block at 80°C and 95°C for 20, 30, and 90 min. Twenty untreated specimens served as a positive control, and bacterial growth was followed up for 12 weeks. Our results showed that 90 min of heat inactivation was necessary for samples with two loops of biomass. Further protein extraction and a matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) MS assay demonstrated adequate scores for bacterial identification (≥1.7), with the highest score achieved in the 80°C/90 min and 95°C/30 min treatment groups. A proteomics study also confidently identified 648 proteins with ∼93% to 96% consistent protein abundances following heating at 95°C for 20, 30, and 90 min. Heat inactivation at 95°C for 90 min yielded the most quantifiable proteins, and a functional analysis revealed proteins located in the ribosomal subunit. In summary, we proposed a heat inactivation method for the M. tuberculosis strain H37Rv and studied the preservation of protein components for subsequent bacterial identification and protein-related assays.

IMPORTANCE Inactivation of Mycobacterium tuberculosis is an important step to guarantee biosafety for subsequent M. tuberculosis identification and related research, notably in areas of endemicity with minimal resources. However, certain biomolecules might be denatured or hydrolyzed because of the harsh inactivation process, and a standardized protocol is yet to be determined. We evaluated distinct heating conditions to report the inactivation efficiency and performed downstream mass spectrometry-based M. tuberculosis identification and proteomics study. The results are important and useful for both basic and clinical M. tuberculosis studies.

Efficacy of epetraborole against Mycobacterium abscessus is increased with norvaline

Mycobacterium abscessus is the most common rapidly growing non-tuberculous mycobacteria to cause pulmonary disease in patients with impaired lung function such as cystic fibrosis. M. abscessus displays high intrinsic resistance to common antibiotics and inducible resistance to macrolides like clarithromycin. As such, M. abscessus is clinically resistant to the entire regimen of front-line M. tuberculosis drugs, and treatment with antibiotics that do inhibit M. abscessus in the lab results in cure rates of 50% or less. Here, we identified epetraborole (EPT) from the MMV pandemic response box as an inhibitor against the essential protein leucyl-tRNA synthetase (LeuRS) in M. abscessus. EPT protected zebrafish from lethal M. abscessus infection and did not induce self-resistance nor against clarithromycin. Contrary to most antimycobacterials, the whole-cell activity of EPT was greater against M. abscessus than M. tuberculosis, but crystallographic and equilibrium binding data showed that EPT binds LeuRS_Mabs and LeuRS_Mtb with similar residues and dissociation constants. Since EPT-resistant M. abscessus mutants lost LeuRS editing activity, these mutants became susceptible to misaminoacylation with leucine mimics like the non-proteinogenic amino acid norvaline. Proteomic analysis revealed that when M. abscessus LeuRS mutants were fed norvaline, leucine residues in proteins were replaced by norvaline, inducing the unfolded protein response with temporal changes in expression of GroEL chaperonins and Clp proteases. This supports our in vitro data that supplementation of media with norvaline reduced the emergence of EPT mutants in both M. abscessus and M. tuberculosis. Furthermore, the combination of EPT and norvaline had improved in vivo efficacy compared to EPT in a murine model of M. abscessus infection. Our results emphasize the effectiveness of EPT against the clinically relevant cystic fibrosis pathogen M. abscessus, and these findings also suggest norvaline adjunct therapy with EPT could be beneficial for M. abscessus and other mycobacterial infections like tuberculosis.

Current antimycobacterial drugs are inadequate to handle the increasing number of non-tuberculous mycobacteria infections that eclipse tuberculosis infections in many developed countries. Of particular importance for cystic fibrosis patients, Mycobacterium abscessus is notoriously difficult to treat where patients spend extended time on antibiotics with cure rates comparable to extreme drug resistant M. tuberculosis. Here, we identified epetraborole (EPT) with in vitro and in vivo activities against M. abscessus. We showed that EPT targets the editing domain of the leucyl-tRNA synthetase (LeuRS) and that escape mutants lost LeuRS editing activity, making these mutants susceptible to misaminoacylation with leucine mimics. Most importantly, combination therapy of EPT and norvaline limited the rate of EPT resistance in both M. abscessus and M. tuberculosis, and this was the first study to demonstrate improved in vivo efficacy of EPT and norvaline compared to EPT in a murine model of M. abscessus pulmonary infection. The demonstration of norvaline adjunct therapy with EPT for M. abscessus infections is promising for cystic fibrosis patients and could translate to other mycobacterial infections, such as tuberculosis.

Regulation of Ribosomal Protein Synthesis in Mycobacteria: The Autogenous Control of rpsO

The autogenous regulation of ribosomal protein (r-protein) synthesis plays a key role in maintaining the stoichiometry of ribosomal components in bacteria. In this work, taking the rpsO gene as a classic example, we addressed for the first time the in vivo regulation of r-protein synthesis in the mycobacteria M. smegmatis (Msm) and M. tuberculosis (Mtb). We used a strategy based on chromosomally integrated reporters under the control of the rpsO regulatory regions and the ectopic expression of Msm S15 to measure its impact on the reporter expression. Because the use of E. coli as a host appeared inefficient, a fluorescent reporter system was developed by inserting Msm or Mtb rpsO-egfp fusions into the Msm chromosome and expressing Msm S15 or E. coli S15 in trans from a novel replicative shuttle vector, pAMYC. The results of the eGFP expression measurements in Msm cells provided evidence that the rpsO gene in Msm and Mtb was feedback-regulated at the translation level. The mutagenic analysis showed that the folding of Msm rpsO 5'UTR in a pseudoknot appeared crucial for repression by both Msm S15 and E. coli S15, thus indicating a striking resemblance of the rpsO feedback control in mycobacteria and in E. coli.

CD38 +CD27 -TNF-α + on Mtb-specific CD4 + T is a robust biomarker for tuberculosis diagnosis

BACKGROUND

Early and accurate diagnosis followed by timely treatment are the key prerequisites to fight tuberculosis (TB) and reduce its global burden. Despite scientific advances, the rapid and correct diagnosis of both pulmonary and extrapulmonary tuberculosis remains a challenge due to traditional reliance on detection of the elusive bacilli. Mycobacterium tuberculosis (Mtb)-specific host immune activation and cytokine production have shown significant promise as alternative means of detecting and distinguishing active disease from latent infection. We queried the diagnostic ability of phenotypic markers on Mtb-specific cytokine-producing immune cell subsets for identifying active tuberculosis.

METHODS

Subjects belonging to the following groups were recruited - pulmonary and extrapulmonary TB, latent TB, cured TB, sick controls and healthy controls. Polychromatic flow cytometry was used to identify host immune biomarkers in an exploratory cohort comprising 56 subjects using peripheral blood mononuclear cells. Clinical performance of the identified biomarker was evaluated using whole blood in a blinded validation cohort comprising 165 individuals.

RESULTS

Cytokine secreting frequencies of Mtb-specific CD4 + T cells with CD38 +CD27 - phenotype clearly distinguished infected individuals with active tuberculosis from those without disease. TNF-α secretion from CD38 +CD27 -CD4 + T cells upon stimulation with ESAT6/CFP10 peptides had the best diagnostic accuracy at a cut-off of 9.91% [exploratory: 96.67% specificity, 88.46% sensitivity; validation: 96.15% specificity, 90.16% sensitivity]. Additionally, this subset differentiated treatment-naive TB patients from individuals cured of TB following completion of anti-tuberculosis therapy.

CONCLUSIONS

Mtb-specific CD38 +CD27 -TNF-α +CD4 + T cell subset is a robust biomarker both for diagnosing tuberculosis and assessing cure.

Method of extraction and proteome profiling of mycobacteria using liquid chromatography-high resolution mass spectrometry

Advances in massively parallel sequencing, of complete bacterial genomes, have led to many novel findings in the field of genomics. However, these data often lack correlation with expressed protein profiles. It has been demonstrated that even very closely related genomes, such as in mycobacteria, express drastically different phenotypes. These phenotypes often have major roles in pathogenicity. Therefore, it is just as important to have a method for examining the proteome of a bacterium as well as its genome. These studies are further complicated in mycobacteria due to the cell wall and mycolic acid. A comprehensive method for the identification and characterization of the whole mycobacterium protein profile is needed. In the present study, a simple, sensitive, and specific liquid chromatography tandem mass spectrometry method was developed for the extraction, purification and profiling the mycobacterial proteome in various species. During development, sonication and bead-beating cell lysis protocol was tested using 15% Acetonitrile and 6 M guanidine-HCl (GuHCl) as extraction solvent. Sonication lysis in 6 M GuHCl with glass beads was the preferred method for cell lysis. This method was developed using reverse phase liquid chromatography and a Q Exactive ™ Plus Orbitrap™ mass spectrometer for peptide and protein identification. Bottom-up liquid chromatography-mass spectrometry LC–MS analysis resulted in identification of greater than 2500 proteins.

Improvement of Mycobacterium tuberculosis detection in sputum using DNA extracted by sonication

Tuberculosis (TB) is one of the infectious diseases with high mortality in the world. DNA amplification techniques have been used to overcome barriers to the diagnosis of this disease. However, the success of these methodologies is highly dependent on the DNA obtained from the sample. This study was carried out to verify whether the DNA extracted by sonication (in house method) could yield suitable DNA for amplification by real-time PCR (qPCR). Sixty sputum samples were submitted to DNA extraction using sonication compared to a commercial method (Detect-TB kit, Labtest/MG-Brazil). All DNA samples were amplified by qPCR for IS6110 region (IS6110-qPCR/SYBR Green assay). Out of 60 samples, 40 were positive for TB; of these, all had positive results when extracted by sonication (100%) and 80% when extracted by the commercial method. The limit of detection (LOD) of Mycobacterium tuberculosis (H37Rv strain) by qPCR was 14 CFU/mL when the DNA was extracted by sonication, compared to countless colonies when extracted by commercial kit. In conclusion, the sonication protocol (without purification step) proved to be a simple, fast, and suitable method for obtaining DNA for use in qPCR from sputum samples.

Recent advances in production and extraction of bacterial lipids for biofuel production

Lipid-based biofuel is a clean and renewable energy that has been recognized as a promising replacement for petroleum-based fuels. Lipid-based biofuel can be made from three different types of intracellular biolipids; triacylglycerols (TAGs), wax esters (WEs), and polyhydroxybutyrate (PHB). Among many lipid-producing prokaryotes and eukaryotes, biolipids from prokaryotes have been recently highlighted due to simple cultivation of lipid-producing prokaryotes and their ability to accumulate high biolipid contents. However, the cost of lipid-based biofuel production remains high, in part, because of high cost of lipid extraction processes. This review summarizes the production mechanisms of these different types of biolipids from prokaryotes and extraction methods for these biolipids. Traditional and improved physical/chemical approaches for biolipid extraction remain costly, and these methods are summarized and compared in this review. Recent advances in biological lipid extraction including phage-based cell lysis or secretion of biolipids are also discussed. These new techniques are promising for bacterial biolipids extraction. Challenges and future research needs for cost-effective lipid extraction are identified in this review.

Assessment of seven protocols to prepare Cutibacterium acnes bacterial lysates to measure its immunogenic potential and review of the literature

Seven protocols were tested to prepare cell wall extracts from live Cutibacterium acnes. Different parameters were modified: thawing/freezing and sonication/freezing cycles, to impact on mechanical degradation of the bacteria. Finally, the immunogenic potential of the extracts generated was evaluated by measuring IL-8 releases using an in vitro skin explants system. The aim of this article was to compare the existing protocols from the scientific literature, and also propose a standardized method developed in our facilities.

Uncloaking an ancient adversary: Can pathogen biomarker elicitors play a role in confirming extrapulmonary TB and latent TB infection?

Latent tuberculosis infection (LTBI) is diagnosed immunologically using the Mantoux tuberculin skin test (TST) or interferon-gamma release assays (IGRAs). While widely used, immunodiagnostics can produce false negative or false positive results. Pathogen biomarkers provide an alternative, but direct detection in LTBI and extrapulmonary TB cases is challenging. Mycobacterium tuberculosis grows slowly, has limited hematogenous movement, is protected by a lipid rich cell wall, and produces low levels of secreted factors. Here we discuss the potential of elicitors by first considering pathogen markers that may be released following the administration of isoniazid. Isoniazid targets the cell wall of mycobacteria found in extracellular compartments and within monocytes, macrophages, dendritic cells, and lymphatic endothelial cells. Isoniazid's dual-purpose potential as an antibiotic and elicitor is supported by knowledge of latent infection dynamics, time-kill kinetics, and new detection techniques. Within hours, the bactericidal action of isoniazid likely enriches plasma with M. tuberculosis DNA, RNA, proteins/peptides, and lipids. Undoubtedly a portion of these biomarkers are eliminated as some bacilli undergo phagocytosis and lysosomal destruction. However, advances in immunoprecipitation and nucleic acid amplification, combined with the use of larger blood volumes during assay development, may overcome these losses. Other anticipated challenges include determining optimal sample collection times and designing diagnostic workflows that minimize processing-associated marker loss and degradation. Conventional, commercial, and emerging technologies that address these variables are discussed. If realized, isoniazid associated markers could provide proof of concept for novel elicitor-based diagnostic approaches capable of confirming LTBI and empirically treated extrapulmonary TB.

Comprehensive Analysis and Comparison on the Codon Usage Pattern of Whole Mycobacterium tuberculosis Coding Genome from Different Area

Phenomenon of unequal use of synonymous codons in Mycobacterium tuberculosis is common. Codon usage bias not only plays an important regulatory role at the level of gene expression, but also helps in improving the accuracy and efficiency of translation. Meanwhile, codon usage pattern of Mycobacterium tuberculosis genome is important for interpreting evolutionary characteristics in species. In order to investigate the codon usage pattern of the Mycobacterium tuberculosis genome, 12 Mycobacterium tuberculosis genomes from different area are downloaded from the GeneBank. The correlations between G₃, GC₁₂, whole GC content, codon adaptation index, codon bias index, and so on of Mycobacterium tuberculosis genomes are calculated. The ENC-plot, relationship between A₃/(A₃ + T₃) and G₃/(G₃ + C₃), GC₁₂ versus GC₃ plot, and the RSCU of overall/separated genomes all show that the codon usage bias exists in all 12 Mycobacterium tuberculosis genomes. Lastly, relationship between CBI and the equalization of ENC shows a strong negative correlation between them. The relationship between protein length and GC content (GC₃ and GC₁₂) shows that more obvious differences in the GC content may be in shorter protein. These results show that codon usage bias existing in the Mycobacterium tuberculosis genomes could be used for further study on their evolutionary phenomenon.