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Santoshi M, Tare P, Nagaraja V. Nucleoid-associated proteins of mycobacteria come with a distinctive flavor. Mol Microbiol 2024. [PMID: 38922783 DOI: 10.1111/mmi.15287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Revised: 05/31/2024] [Accepted: 06/05/2024] [Indexed: 06/28/2024]
Abstract
In every bacterium, nucleoid-associated proteins (NAPs) play crucial roles in chromosome organization, replication, repair, gene expression, and other DNA transactions. Their central role in controlling the chromatin dynamics and transcription has been well-appreciated in several well-studied organisms. Here, we review the diversity, distribution, structure, and function of NAPs from the genus Mycobacterium. We highlight the progress made in our understanding of the effects of these proteins on various processes and in responding to environmental stimuli and stress of mycobacteria in their free-living as well as during distinctive intracellular lifestyles. We project them as potential drug targets and discuss future studies to bridge the information gap with NAPs from well-studied systems.
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Affiliation(s)
- Meghna Santoshi
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
| | - Priyanka Tare
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
| | - Valakunja Nagaraja
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India
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2
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Wang S, Fang R, Wang H, Li X, Xing J, Li Z, Song N. The role of transcriptional regulators in metal ion homeostasis of Mycobacterium tuberculosis. Front Cell Infect Microbiol 2024; 14:1360880. [PMID: 38529472 PMCID: PMC10961391 DOI: 10.3389/fcimb.2024.1360880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2023] [Accepted: 02/27/2024] [Indexed: 03/27/2024] Open
Abstract
Metal ions are essential trace elements for all living organisms and play critical catalytic, structural, and allosteric roles in many enzymes and transcription factors. Mycobacterium tuberculosis (MTB), as an intracellular pathogen, is usually found in host macrophages, where the bacterium can survive and replicate. One of the reasons why Tuberculosis (TB) is so difficult to eradicate is the continuous adaptation of its pathogen. It is capable of adapting to a wide range of harsh environmental stresses, including metal ion toxicity in the host macrophages. Altering the concentration of metal ions is the common host strategy to limit MTB replication and persistence. This review mainly focuses on transcriptional regulatory proteins in MTB that are involved in the regulation of metal ions such as iron, copper and zinc. The aim is to offer novel insights and strategies for screening targets for TB treatment, as well as for the development and design of new therapeutic interventions.
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Affiliation(s)
- Shuxian Wang
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
| | - Ren Fang
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
| | - Hui Wang
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
| | - Xiaotian Li
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
| | - Jiayin Xing
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
| | - Zhaoli Li
- Drug Innovation Research Center, SAFE Pharmaceutical Technology Co. Ltd., Beijing, China
| | - Ningning Song
- Key Laboratory of Respiratory Tract Pathogens and Drug Therapy, School of Life Science and Technology, Shandong Second Medical University, Weifang, China
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Yu X, Jiang S, Li Y, Zhou H, Wei Y, Li X, Zhang Y, Hu P, Wu H, Wang H, Wu S, Zhang S. Development of a new cellular immunological detection method for tuberculosis based on HupB protein induced IL-6 release test. Front Microbiol 2023; 14:1148503. [PMID: 37077246 PMCID: PMC10106748 DOI: 10.3389/fmicb.2023.1148503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 03/14/2023] [Indexed: 04/05/2023] Open
Abstract
ObjectiveAs a virulence factor, HupB plays important roles in the survival of MTB after infection and modulates the host immune response. In the current study, we aim to explore a new cellular immunological detection method for tuberculosis infection detection based on HupB protein.MethodsHupB was used to stimulate PBMCs extracted from pulmonary tuberculosis (PTB) patients, and secreted cytokines was examined. Then, we constructed a single center and a multi-center clinical trials to collect PBMCs from PTB patients, nPTB patients, or healthy volunteers to verify our findings.ResultsCytokine’s screening illustrated that IL-6 was the only cytokine released after HupB stimulation. Single-center and multi-center clinical trials showed that HupB stimulation significantly increased the level of IL-6 in the supernatant of PBMCs from PTB patients. Then we compared the specificity and sensitivity of HupB induced IL-6 release assay with ESAT-6 and CFP10 induced interferon γ release assay (IGRA), and found in smear positive PTB patients, the specificity and sensitivity of HupB induced IL-6 release assay was better than IGRA, and in smear negative PTB patients, the sensitivity was better. Combination of both assays provided an improved specificity and sensitivity for tuberculosis diagnosis.ConclusionThis study explored an immunological detection method for tuberculosis infection cells based on HupB protein-induced IL-6 release test, which can be used to enhance the diagnosis diagnostic accuracy of TB.
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Affiliation(s)
- Xiaoli Yu
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Shengsheng Jiang
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Yang Li
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Huaiheng Zhou
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Yutong Wei
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Xuefang Li
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Ye Zhang
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Peng Hu
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Haoming Wu
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Hualin Wang
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
- *Correspondence: Hualin Wang,
| | - Shimin Wu
- Center for Clinical Laboratory, General Hospital of the Yangtze River Shipping, Wuhan Brain Hospital, Wuhan, China
- Shimin Wu,
| | - Shulin Zhang
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
- Department of Immunology and Microbiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shulin Zhang,
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Choudhury M, Virivinti J, Kandi S, Sritharan V, Sritharan M. Th2 immune response by the iron-regulated protein HupB of Mycobacterium tuberculosis. Indian J Tuberc 2022; 69:90-99. [PMID: 35074158 DOI: 10.1016/j.ijtb.2021.04.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Accepted: 04/06/2021] [Indexed: 06/14/2023]
Abstract
BACKGROUND HupB is an iron-regulated protein essential for the growth of Mycobacterium tuberculosis inside macrophages. To investigate if HupB induced a dominant Th2 type immune response, we studied the effect of rHupB on PBMCs from TB patients and by infecting mouse macrophages with wild type and hupB KO mutants. METHODS PBMCs from pulmonary TB (n = 60), extra pulmonary TB (n = 23) and healthy controls (n = 30) were stimulated with purified HupB and the cytokines secreted were assayed. The sera were screened for anti-HupB antibodies by ELISA. Mouse macrophages cell line (RAW 264.7) was infected with wild type, hupB KO and hupB-complemented strains of M. tuberculosis grown in high and low iron medium and the expression of cytokines was assayed by qRT-PCR. RESULTS Murine macrophages infected with the hupB KO strain produced low levels of the pro-inflammatory cytokines IFN-γ, TNF-α, IL-1, and IL-18 and high levels of IL-10. HupB induced IL-6 and IL-10 production in PBMCs of TB patients and down-regulated IFN-γ and TNF-α production. The influence of HupB was remarkable in the EPTB group. CONCLUSION HupB shifted the immune response to the Th2 type. Low IFN-γ and elevated IL-10 in EPTB patients is noteworthy.
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Affiliation(s)
- Mitali Choudhury
- Department of Animal Biology, University of Hyderabad, Hyderabad, 500046, India
| | - Jahnavi Virivinti
- Molecular Diagnostics and Biomarkers Lab, Global Hospitals, Hyderabad, 500004, India
| | - Subhakar Kandi
- Kamineni Academy of Medical Sciences and Research Centre, Hyderabad, 500038, India
| | | | - Manjula Sritharan
- Department of Animal Biology, University of Hyderabad, Hyderabad, 500046, India.
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Baatjies L, Loxton AG, Williams MJ. Host and Bacterial Iron Homeostasis, an Underexplored Area in Tuberculosis Biomarker Research. Front Immunol 2021; 12:742059. [PMID: 34777355 PMCID: PMC8586213 DOI: 10.3389/fimmu.2021.742059] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 10/14/2021] [Indexed: 01/10/2023] Open
Abstract
Mycobacterium tuberculosis (Mtb) "a human adapted pathogen" has found multiple ways to manipulate the host immune response during infection. The human immune response to Mtb infection is a highly complex cascade of reactions, with macrophages as preferred intracellular location. Interaction with the host through infection gives rise to expression of specific gene products for survival and multiplication within the host. The signals that the pathogens encounter during infection cause them to selectively express genes in response to signals. One strategy to identify Mtb antigens with diagnostic potential is to identify genes that are specifically induced during infection or in specific disease stages. The shortcomings of current immunodiagnostics include the failure to detect progression from latent infection to active tuberculosis disease, and the inability to monitor treatment efficacy. This highlights the need for new tuberculosis biomarkers. These biomarkers should be highly sensitive and specific diagnosing TB infection, specifically distinguishing between latent infection and active disease. The regulation of iron levels by the host plays a crucial role in the susceptibility and outcome of Mtb infection. Of interest are the siderophore biosynthetic genes, encoded by the mbt-1 and mbt-2 loci and the SUF (mobilization of sulphur) operon (sufR-sufB-sufD-sufC-csd-nifU-sufT), which encodes the primary iron-sulphur cluster biogenesis system. These genes are induced during iron limitation and intracellular growth of Mtb, pointing to their importance during infection.
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Affiliation(s)
- Lucinda Baatjies
- Department of Science and Innovation (DSI)-National Research Foundation (NRF) Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - Andre G. Loxton
- Department of Science and Innovation (DSI)-National Research Foundation (NRF) Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - Monique J. Williams
- Department of Science and Innovation (DSI)-National Research Foundation (NRF) Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
- Department of Molecular and Cell Biology, University of Cape Town, Cape Town, South Africa
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Trutneva KA, Avdienko VG, Demina GR, Shleeva MO, Shumkov MS, Salina EG, Kaprelyants AS. Immunoreactive Proteins of Dormant Mycobacterium tuberculosis Cells. APPL BIOCHEM MICRO+ 2021. [DOI: 10.1134/s0003683821020174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Abstract
The protein profile of dormant Mtb obtained after the gradual acidification of Mtb culture was studied to find antigenic proteins for humans that are expressed by M. tuberculosis (Mtb) cells in vitro under conditions close to the situation of persistence in vivo. According to 2D electrophoresis, a significant diversity of proteins in dormant cells was found. However, the representation of individual proteins in dormant versus active cells differed substantially. Immunoblotting in different protein fractions of dormant cells revealed ten proteins that are able to bind antibodies in pooled sera of TB patients. Two proteins (Rv2018 and Rv0341) are new immunogenics that were not previously found in other studies. Four proteins (Rv0341, Rv2018, Rv1509, Rv2986) with the maximal structural specificity for Mtb due to their unique extended domains were selected for further analysis. These proteins were expressed in E. coli cells and studied via enzyme-linked immunosorbent assay (ELISA) for the immunogenicity of individual sera of TB patients and healthy donors. All proteins were found to have the ability to react with individual sera of TB patients. In TB patients, 5–45% (depending on the particulate protein) have a titer that is higher than the average titers of healthy donors +SD; the most immunogenic was protein Rv2986. Thus, the application of phenotypically changed (dormant) Mtb cells makes it possible to identify a specific repertoire of immunodominant proteins that could be used in the construction of polypeptides that are useful for the serodiagnosis of active/latent TB.
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Sustained elevated levels of C-reactive protein and ferritin in pulmonary tuberculosis patients remaining culture positive upon treatment initiation. PLoS One 2017; 12:e0175278. [PMID: 28384354 PMCID: PMC5383283 DOI: 10.1371/journal.pone.0175278] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 03/23/2017] [Indexed: 11/19/2022] Open
Abstract
Background Clinical trials that evaluate new anti-tubercular drugs and treatment regimens take years to complete due to the slow clearance of Mycobacterium tuberculosis infection and the lack of early biomarkers that predict treatment outcomes. Host Inflammation markers have been associated with tuberculosis (TB) pathogenesis. In the present study, we tested if circulating levels of C-reactive protein (CRP) and ferritin reflect mycobacterial loads and inflammation in pulmonary TB (PTB) patients undergoing anti-tuberculous therapy (ATT). Methods Prospective measurements of CRP and ferritin, used as readouts of systemic inflammation, were performed in cryopreserved serum samples from 165 Brazilian patients with active PTB initiating ATT. Associations between levels of these laboratory parameters with mycobacterial loads in sputum as well as with sputum conversion at day 60 of ATT were tested. Results Circulating levels of both ferritin and CRP gradually decreased over time on ATT. At pre-treatment, concentrations of these parameters were unable to distinguish patients with positive from those with negative acid-fast bacilli (AFB) in sputum cultures. However, patients who remained with positive cultures at day 60 of ATT exhibited heightened levels of these inflammatory markers compared to those with negative cultures at that time point. Conclusions CRP and Ferritin levels in serum may be useful to identify patients with positive cultures at day 60 of ATT.
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Iron Homeostasis in Mycobacterium tuberculosis: Mechanistic Insights into Siderophore-Mediated Iron Uptake. J Bacteriol 2016; 198:2399-409. [PMID: 27402628 DOI: 10.1128/jb.00359-16] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mycobacterium tuberculosis requires iron for normal growth but faces a limitation of the metal ion due to its low solubility at biological pH and the withholding of iron by the mammalian host. The pathogen expresses the Fe(3+)-specific siderophores mycobactin and carboxymycobactin to chelate the metal ion from insoluble iron and the host proteins transferrin, lactoferrin, and ferritin. Siderophore-mediated iron uptake is essential for the survival of M. tuberculosis, as knockout mutants, which were defective in siderophore synthesis or uptake, failed to survive in low-iron medium and inside macrophages. But as excess iron is toxic due to its catalytic role in the generation of free radicals, regulation of iron uptake is necessary to maintain optimal levels of intracellular iron. The focus of this review is to present a comprehensive overview of iron homeostasis in M. tuberculosis that is discussed in the context of mycobactin biosynthesis, transport of iron across the mycobacterial cell envelope, and storage of excess iron. The clinical significance of the serum iron status and the expression of the iron-regulated protein HupB in tuberculosis (TB) patients is presented here, highlighting the potential of HupB as a marker, notably in extrapulmonary TB cases.
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Sritharan N, Choudhury M, Sivakolundu S, Chaurasia R, Chouhan N, Rao PP, Sritharan M. Highly immunoreactive antibodies against the rHup-F2 fragment (aa 63-161) of the iron-regulated HupB protein of Mycobacterium tuberculosis and its potential for the serodiagnosis of extrapulmonary and recurrent tuberculosis. Eur J Clin Microbiol Infect Dis 2014; 34:33-40. [PMID: 25037869 DOI: 10.1007/s10096-014-2203-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 06/30/2014] [Indexed: 11/30/2022]
Abstract
HupB is an iron-regulated protein in Mycobacterium tuberculosis that functions as a positive regulator of mycobactin biosynthesis. It is essential for the growth and survival of the pathogen inside macrophages. Previously, using the full-length rHupB of M. tuberculosis, we demonstrated high levels of anti-HupB antibodies in the serum of pulmonary tuberculosis (TB) and, interestingly, extrapulmonary TB patients with negligible levels in household contacts and healthy controls. Here, we used three antigenic fragments of HupB, namely the recombinant HupB-F1 (aa 1-71), HupB-F2 (aa 63-161) and HupB-F3 (aa 164-214), as antigens in enzyme-linked immunosorbent assay (ELISA) to screen serum from TB patients. HupB-F2 showed enhanced immunoreactivity with serum from patients with pulmonary TB (three groups consisting of new cases, defaulters and recurrent cases) and extrapulmonary TB, with negligible levels in normal healthy controls. The negative correlation of the anti-(HupB-F2) antibodies with serum iron was maximal, with a Pearson's correlation coefficient value of -0.415. The study, in addition to strengthening the diagnostic potential of HupB, reflected the superior performance of HupB-F2 as an antigen in screening pulmonary and extrapulmonary TB.
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Affiliation(s)
- N Sritharan
- NRI Academy of Sciences, Guntur, Andhra Pradesh, India
| | - M Choudhury
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. CR Rao Road, Gachibowli, Hyderabad, 500 046, India
| | - S Sivakolundu
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. CR Rao Road, Gachibowli, Hyderabad, 500 046, India
| | - R Chaurasia
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. CR Rao Road, Gachibowli, Hyderabad, 500 046, India
| | - N Chouhan
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. CR Rao Road, Gachibowli, Hyderabad, 500 046, India
| | - P P Rao
- NRI Academy of Sciences, Guntur, Andhra Pradesh, India
| | - M Sritharan
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. CR Rao Road, Gachibowli, Hyderabad, 500 046, India.
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Pandey SD, Choudhury M, Sritharan M. Transcriptional regulation of Mycobacterium tuberculosis hupB gene expression. MICROBIOLOGY-SGM 2014; 160:1637-1647. [PMID: 24858079 DOI: 10.1099/mic.0.079640-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The influence of iron levels on the transcription of the hupB gene in Mycobacterium tuberculosis is the focus of this study. Studies in our laboratory showed HupB to be co-expressed with the two siderophores in low-iron organisms. Mycobactin biosynthesis is repressed by the IdeR-Fe(2+) complex that binds the IdeR box in the mbtB promoter. Recently, we demonstrated the positive regulatory effect of HupB on mycobactin biosynthesis by demonstrating its binding to a 10 bp HupB box in the mbtB promoter. Earlier, we observed that HupB, expressed maximally in low-iron media (0.02 µg Fe ml(-1); 0.36 µM Fe) was still detectable at 8 µg Fe ml(-1) (144 µM Fe) when the siderophores were absent and complete repression was seen only at 12 µg Fe ml(-1) (216 µM Fe). In this study, we observed elevated levels of hupB transcripts in iron-limited organisms. IdeR, and not FurA, functioned as the iron regulator, by binding to two IdeR boxes in the hupB promoter. Interestingly, the 10 bp HupB box, first reported in the mbtB promoter, was identified in the hupB promoter. Using DNA footprinting and electrophoretic mobility shift assays, we demonstrated the functionality of the HupB box and the two IdeR boxes. The high hupB transcript levels expressed by the organism and the in vitro protein-DNA interaction studies led us to hypothesize the sequence of events occurring in response to changes in the intracellular iron concentration, emphasizing the roles played by IdeR and HupB in iron homeostasis.
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Affiliation(s)
- Satya Deo Pandey
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. C.R. Rao Road, Gachibowli, Hyderabad 500046, India
| | - Mitali Choudhury
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. C.R. Rao Road, Gachibowli, Hyderabad 500046, India
| | - Manjula Sritharan
- Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Prof. C.R. Rao Road, Gachibowli, Hyderabad 500046, India
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Iron-regulated protein HupB of Mycobacterium tuberculosis positively regulates siderophore biosynthesis and is essential for growth in macrophages. J Bacteriol 2014; 196:1853-65. [PMID: 24610707 DOI: 10.1128/jb.01483-13] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mycobacterium tuberculosis expresses the 28-kDa protein HupB (Rv2986c) and the Fe(3+)-specific high-affinity siderophores mycobactin and carboxymycobactin upon iron limitation. The objective of this study was to understand the functional role of HupB in iron acquisition. A hupB mutant strain of M. tuberculosis, subjected to growth in low-iron medium (0.02 μg Fe ml(-1)), showed a marked reduction of both siderophores with low transcript levels of the mbt genes encoding the MB biosynthetic machinery. Complementation of the mutant strain with hupB restored siderophore production to levels comparable to that of the wild type. We demonstrated the binding of HupB to the mbtB promoter by both electrophoretic mobility shift assays and DNA footprinting. The latter revealed the HupB binding site to be a 10-bp AT-rich region. While negative regulation of the mbt machinery by IdeR is known, this is the first report of positive regulation of the mbt operon by HupB. Interestingly, the mutant strain failed to survive inside macrophages, suggesting that HupB plays an important role in vivo.
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