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Wang M, Nie Y, Wu XL. Extracellular heme recycling and sharing across species by novel mycomembrane vesicles of a Gram-positive bacterium. THE ISME JOURNAL 2021; 15:605-617. [PMID: 33037324 PMCID: PMC8027190 DOI: 10.1038/s41396-020-00800-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/16/2020] [Accepted: 09/28/2020] [Indexed: 12/26/2022]
Abstract
Microbes spontaneously release membrane vesicles (MVs), which play roles in nutrient acquisition and microbial interactions. Iron is indispensable for microbes, but is a difficult nutrient to acquire. However, whether MVs are also responsible for efficient iron uptake and therefore involved in microbial interaction remains to be elucidated. Here, we used a Gram-positive strain, Dietzia sp. DQ12-45-1b, to analyze the function of its MVs in heme-iron recycling and sharing between species. We determined the structure and constituent of MVs and showed that DQ12-45-1b releases MVs originating from the mycomembrane. When comparing proteomes of MVs between iron-limiting and iron-rich conditions, we found that under iron-limiting conditions, heme-binding proteins are enriched. Next, we proved that MVs participate in extracellular heme capture and transport, especially in heme recycling from environmental hemoproteins. Finally, we found that the heme carried in MVs is utilized by multiple species, and we further verified that membrane fusion efficiency and species evolutionary distance determine heme delivery. Together, our findings strongly suggest that MVs act as a newly identified pathway for heme recycling, and represent a public good shared between phylogenetically closely related species.
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Affiliation(s)
- Meng Wang
- College of Engineering, Peking University, 100871, Beijing, China
| | - Yong Nie
- College of Engineering, Peking University, 100871, Beijing, China.
| | - Xiao-Lei Wu
- College of Engineering, Peking University, 100871, Beijing, China.
- Institute of Ocean Research, Peking University, 100871, Beijing, China.
- Institute of Ecology, Peking University, 100871, Beijing, China.
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2
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Chateau A, Van der Verren SE, Remaut H, Fioravanti A. The Bacillus anthracis Cell Envelope: Composition, Physiological Role, and Clinical Relevance. Microorganisms 2020; 8:E1864. [PMID: 33255913 PMCID: PMC7759979 DOI: 10.3390/microorganisms8121864] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 11/23/2020] [Accepted: 11/24/2020] [Indexed: 12/31/2022] Open
Abstract
Anthrax is a highly resilient and deadly disease caused by the spore-forming bacterial pathogen Bacillus anthracis. The bacterium presents a complex and dynamic composition of its cell envelope, which changes in response to developmental and environmental conditions and host-dependent signals. Because of their easy to access extracellular locations, B. anthracis cell envelope components represent interesting targets for the identification and development of novel therapeutic and vaccine strategies. This review will focus on the novel insights regarding the composition, physiological role, and clinical relevance of B. anthracis cell envelope components.
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Affiliation(s)
- Alice Chateau
- Avignon Université, INRAE, UMR SQPOV, F-84914 Avignon, France;
| | - Sander E. Van der Verren
- Structural and Molecular Microbiology, Structural Biology Research Center, VIB, 1050 Brussels, Belgium; (S.E.V.d.V.); (H.R.)
- Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium
| | - Han Remaut
- Structural and Molecular Microbiology, Structural Biology Research Center, VIB, 1050 Brussels, Belgium; (S.E.V.d.V.); (H.R.)
- Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium
| | - Antonella Fioravanti
- Structural and Molecular Microbiology, Structural Biology Research Center, VIB, 1050 Brussels, Belgium; (S.E.V.d.V.); (H.R.)
- Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium
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3
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Macdonald R, Mahoney BJ, Ellis-Guardiola K, Maresso A, Clubb RT. NMR experiments redefine the hemoglobin binding properties of bacterial NEAr-iron Transporter domains. Protein Sci 2019; 28:1513-1523. [PMID: 31120610 DOI: 10.1002/pro.3662] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 05/14/2019] [Indexed: 01/02/2023]
Abstract
Iron is a versatile metal cofactor that is used in a wide range of essential cellular processes. During infections, many bacterial pathogens acquire iron from human hemoglobin (Hb), which contains the majority of the body's total iron content in the form of heme (iron protoporphyrin IX). Clinically important Gram-positive bacterial pathogens scavenge heme using an array of secreted and cell-wall-associated receptors that contain NEAr-iron Transporter (NEAT) domains. Experimentally defining the Hb binding properties of NEAT domains has been challenging, limiting our understanding of their function in heme uptake. Here we show that solution-state NMR spectroscopy is a powerful tool to define the Hb binding properties of NEAT domains. The utility of this method is demonstrated using the NEAT domains from Bacillus anthracis and Listeria monocytogenes. Our results are compatible with the existence of at least two types of NEAT domains that are capable of interacting with either Hb or heme. These binding properties can be predicted from their primary sequences, with Hb- and heme-binding NEAT domains being distinguished by the presence of (F/Y)YH(Y/F) and S/YXXXY motifs, respectively. The results of this work should enable the functions of a wide range of NEAT domain containing proteins in pathogenic bacteria to be reliably predicted.
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Affiliation(s)
- Ramsay Macdonald
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, 90095.,UCLA-DOE Institute of Genomics and Proteomics, University of California, Los Angeles, Los Angeles, California, 90095
| | - Brendan J Mahoney
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, 90095.,UCLA-DOE Institute of Genomics and Proteomics, University of California, Los Angeles, Los Angeles, California, 90095
| | - Ken Ellis-Guardiola
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, 90095.,UCLA-DOE Institute of Genomics and Proteomics, University of California, Los Angeles, Los Angeles, California, 90095
| | - Anthony Maresso
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, 77030
| | - Robert T Clubb
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, 90095.,UCLA-DOE Institute of Genomics and Proteomics, University of California, Los Angeles, Los Angeles, California, 90095.,Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California, 90095
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4
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Chao A, Sieminski PJ, Owens CP, Goulding CW. Iron Acquisition in Mycobacterium tuberculosis. Chem Rev 2018; 119:1193-1220. [PMID: 30474981 DOI: 10.1021/acs.chemrev.8b00285] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The highly contagious disease tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis (Mtb), which has been evolving drug resistance at an alarming rate. Like all human pathogens, Mtb requires iron for growth and virulence. Consequently, Mtb iron transport is an emerging drug target. However, the development of anti-TB drugs aimed at these metabolic pathways has been restricted by the dearth of information on Mtb iron acquisition. In this Review, we describe the multiple strategies utilized by Mtb to acquire ferric iron and heme iron. Mtb iron uptake is a complex process, requiring biosynthesis and subsequent export of Mtb siderophores, followed by ferric iron scavenging and ferric-siderophore import into Mtb. Additionally, Mtb possesses two possible heme uptake pathways and an Mtb-specific mechanism of heme degradation that yields iron and novel heme-degradation products. We conclude with perspectives for potential therapeutics that could directly target Mtb heme and iron uptake machineries. We also highlight how hijacking Mtb heme and iron acquisition pathways for drug import may facilitate drug transport through the notoriously impregnable Mtb cell wall.
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Affiliation(s)
| | | | - Cedric P Owens
- Schmid College of Science and Technology , Chapman University , Orange , California 92866 , United States
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5
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Abstract
Iron is an essential micronutrient for both microbes and humans alike. For well over half a century we have known that this element, in particular, plays a pivotal role in health and disease and, most especially, in shaping host-pathogen interactions. Intracellular iron concentrations serve as a critical signal in regulating the expression not only of high-affinity iron acquisition systems in bacteria, but also of toxins and other noted virulence factors produced by some major human pathogens. While we now are aware of many strategies that the host has devised to sequester iron from invading microbes, there are as many if not more sophisticated mechanisms by which successful pathogens overcome nutritional immunity imposed by the host. This review discusses some of the essential components of iron sequestration and scavenging mechanisms of the host, as well as representative Gram-negative and Gram-positive pathogens, and highlights recent advances in the field. Last, we address how the iron acquisition strategies of pathogenic bacteria may be exploited for the development of novel prophylactics or antimicrobials.
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6
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Choo JM, Cheung JK, Wisniewski JA, Steer DL, Bulach DM, Hiscox TJ, Chakravorty A, Smith AI, Gell DA, Rood JI, Awad MM. The NEAT Domain-Containing Proteins of Clostridium perfringens Bind Heme. PLoS One 2016; 11:e0162981. [PMID: 27637108 PMCID: PMC5026354 DOI: 10.1371/journal.pone.0162981] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 08/31/2016] [Indexed: 12/27/2022] Open
Abstract
The ability of a pathogenic bacterium to scavenge iron from its host is important for its growth and survival during an infection. Our studies on C. perfringens gas gangrene strain JIR325, a derivative of strain 13, showed that it is capable of utilizing both human hemoglobin and ferric chloride, but not human holo-transferrin, as an iron source for in vitro growth. Analysis of the C. perfringens strain 13 genome sequence identified a putative heme acquisition system encoded by an iron-regulated surface gene region that we have named the Cht (Clostridium perfringensheme transport) locus. This locus comprises eight genes that are co-transcribed and includes genes that encode NEAT domain-containing proteins (ChtD and ChtE) and a putative sortase (Srt). The ChtD, ChtE and Srt proteins were shown to be expressed in JIR325 cells grown under iron-limited conditions and were localized to the cell envelope. Moreover, the NEAT proteins, ChtD and ChtE, were found to bind heme. Both chtDE and srt mutants were constructed, but these mutants were not defective in hemoglobin or ferric chloride utilization. They were, however, attenuated for virulence when tested in a mouse myonecrosis model, although the virulence phenotype could not be restored via complementation and, as is common with such systems, secondary mutations were identified in these strains. In summary, this study provides evidence for the functional redundancies that occur in the heme transport pathways of this life threatening pathogen.
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Affiliation(s)
- Jocelyn M. Choo
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - Jackie K. Cheung
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - Jessica A. Wisniewski
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - David L. Steer
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Dieter M. Bulach
- Victorian Bioinformatics Consortium, Monash University, Clayton, Victoria, Australia
| | - Thomas J. Hiscox
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - Anjana Chakravorty
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - A. Ian Smith
- Victorian Bioinformatics Consortium, Monash University, Clayton, Victoria, Australia
| | - David A. Gell
- School of Medicine, University of Tasmania, Hobart, Tasmania 7000, Australia
| | - Julian I. Rood
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
| | - Milena M. Awad
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia
- * E-mail:
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7
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Choby JE, Skaar EP. Heme Synthesis and Acquisition in Bacterial Pathogens. J Mol Biol 2016; 428:3408-28. [PMID: 27019298 PMCID: PMC5125930 DOI: 10.1016/j.jmb.2016.03.018] [Citation(s) in RCA: 196] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 03/16/2016] [Accepted: 03/17/2016] [Indexed: 02/06/2023]
Abstract
Bacterial pathogens require the iron-containing cofactor heme to cause disease. Heme is essential to the function of hemoproteins, which are involved in energy generation by the electron transport chain, detoxification of host immune effectors, and other processes. During infection, bacterial pathogens must synthesize heme or acquire heme from the host; however, host heme is sequestered in high-affinity hemoproteins. Pathogens have evolved elaborate strategies to acquire heme from host sources, particularly hemoglobin, and both heme acquisition and synthesis are important for pathogenesis. Paradoxically, excess heme is toxic to bacteria and pathogens must rely on heme detoxification strategies. Heme is a key nutrient in the struggle for survival between host and pathogen, and its study has offered significant insight into the molecular mechanisms of bacterial pathogenesis.
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Affiliation(s)
- Jacob E Choby
- Department of Pathology, Microbiology, & Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Eric P Skaar
- Department of Pathology, Microbiology, & Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA; Tennessee Valley Healthcare System, U.S. Department of Veterans Affairs, Nashville, TN, USA.
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8
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Kim SK, Jung KH, Chai YG. Changes in Bacillus anthracis CodY regulation under host-specific environmental factor deprived conditions. BMC Genomics 2016; 17:645. [PMID: 27530340 PMCID: PMC4987991 DOI: 10.1186/s12864-016-3004-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 08/09/2016] [Indexed: 02/07/2023] Open
Abstract
Background Host-specific environmental factors induce changes in Bacillus anthracis gene transcription during infection. A global transcription regulator, CodY, plays a pivotal role in regulating central metabolism, biosynthesis, and virulence in B. anthracis. In this study, we utilized RNA-sequencing to assess changes in the transcriptional patterns of CodY-regulated B. anthracis genes in response to three conditions of environmental starvation: iron, CO2, or glucose deprivation. In addition, we performed chromatin immunoprecipitation on newly identified CodY-mediated genes. Results Environmental deprivation induced transcriptional changes in CodY-regulated genes in both wild-type and codY null strains, and both CodY-specific and environment-specific patterns were observed. In the iron-depleted condition, overexpression of iron homeostasis genes was observed independent of codY deletion; however, transcription of siderophore and amino acid biosynthesis genes was CodY dependent. Although CodY has a significant regulatory role in central metabolism and the carbon overflow pathway, metabolism-associated genes exhibited CodY-independent expression patterns under glucose starvation. Genes that were differentially expressed in response to CO2 availability showed CodY-dependent regulation, though their maximal expression did require a supply of CO2/bicarbonate. Conclusions We speculate that CodY regulates the expression of environmental-responsive genes in a hierarchical manner and is likely associated with other transcription regulators that are specific for a particular environmental change. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-3004-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Se Kye Kim
- Department of Molecular and Life Science, Hanyang University ERICA, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea
| | - Kyoung Hwa Jung
- Department of Molecular and Life Science, Hanyang University ERICA, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea
| | - Young Gyu Chai
- Department of Molecular and Life Science, Hanyang University ERICA, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea. .,Department of Bionanotechnology, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul, 04763, Republic of Korea.
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9
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Structural Characterization of Heme Environmental Mutants of CgHmuT that Shuttles Heme Molecules to Heme Transporters. Int J Mol Sci 2016; 17:ijms17060829. [PMID: 27240352 PMCID: PMC4926363 DOI: 10.3390/ijms17060829] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 05/19/2016] [Accepted: 05/24/2016] [Indexed: 01/19/2023] Open
Abstract
Corynebacteria contain a heme uptake system encoded in hmuTUV genes, in which HmuT protein acts as a heme binding protein to transport heme to the cognate transporter HmuUV. The crystal structure of HmuT from Corynebacterium glutamicum (CgHmuT) reveals that heme is accommodated in the central cleft with His141 and Tyr240 as the axial ligands and that Tyr240 forms a hydrogen bond with Arg242. In this work, the crystal structures of H141A, Y240A, and R242A mutants were determined to understand the role of these residues for the heme binding of CgHmuT. Overall and heme environmental structures of these mutants were similar to those of the wild type, suggesting that there is little conformational change in the heme-binding cleft during heme transport reaction with binding and the dissociation of heme. A loss of one axial ligand or the hydrogen bonding interaction with Tyr240 resulted in an increase in the redox potential of the heme for CgHmuT to be reduced by dithionite, though the wild type was not reduced under physiological conditions. These results suggest that the heme environmental structure stabilizes the ferric heme binding in CgHmuT, which will be responsible for efficient heme uptake under aerobic conditions where Corynebacteria grow.
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10
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Next-Generation Bacillus anthracis Live Attenuated Spore Vaccine Based on the htrA(-) (High Temperature Requirement A) Sterne Strain. Sci Rep 2016; 6:18908. [PMID: 26732659 PMCID: PMC4702213 DOI: 10.1038/srep18908] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 11/30/2015] [Indexed: 12/17/2022] Open
Abstract
Anthrax is a lethal disease caused by the gram-positive spore-producing bacterium Bacillus anthracis. Live attenuated vaccines, such as the nonencapsulated Sterne strain, do not meet the safety standards mandated for human use in the Western world and are approved for veterinary purposes only. Here we demonstrate that disrupting the htrA gene, encoding the chaperone/protease HtrA (High Temperature Requirement A), in the virulent Bacillus anthracis Vollum strain results in significant virulence attenuation in guinea pigs, rabbits and mice, underlying the universality of the attenuated phenotype associated with htrA knockout. Accordingly, htrA disruption was implemented for the development of a Sterne-derived safe live vaccine compatible with human use. The novel B. anthracis SterneΔhtrA strain secretes functional anthrax toxins but is 10–104-fold less virulent than the Sterne vaccine strain depending on animal model (mice, guinea pigs, or rabbits). In spite of this attenuation, double or even single immunization with SterneΔhtrA spores elicits immune responses which target toxaemia and bacteremia resulting in protection from subcutaneous or respiratory lethal challenge with a virulent strain in guinea pigs and rabbits. The efficacy of the immune-protective response in guinea pigs was maintained for at least 50 weeks after a single immunization.
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11
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Molecular and evolutionary analysis of NEAr-iron Transporter (NEAT) domains. PLoS One 2014; 9:e104794. [PMID: 25153520 PMCID: PMC4143258 DOI: 10.1371/journal.pone.0104794] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 07/18/2014] [Indexed: 12/25/2022] Open
Abstract
Iron is essential for bacterial survival, being required for numerous biological processes. NEAr-iron Transporter (NEAT) domains have been studied in pathogenic Gram-positive bacteria to understand how their proteins obtain heme as an iron source during infection. While a 2002 study initially discovered and annotated the NEAT domain encoded by the genomes of several Gram-positive bacteria, there remains a scarcity of information regarding the conservation and distribution of NEAT domains throughout the bacterial kingdom, and whether these domains are restricted to pathogenic bacteria. This study aims to expand upon initial bioinformatics analysis of predicted NEAT domains, by exploring their evolution and conserved function. This information was used to identify new candidate domains in both pathogenic and nonpathogenic organisms. We also searched metagenomic datasets, specifically sequence from the Human Microbiome Project. Here, we report a comprehensive phylogenetic analysis of 343 NEAT domains, encoded by Gram-positive bacteria, mostly within the phylum Firmicutes, with the exception of Eggerthella sp. (Actinobacteria) and an unclassified Mollicutes bacterium (Tenericutes). No new NEAT sequences were identified in the HMP dataset. We detected specific groups of NEAT domains based on phylogeny of protein sequences, including a cluster of novel clostridial NEAT domains. We also identified environmental and soil organisms that encode putative NEAT proteins. Biochemical analysis of heme binding by a NEAT domain from a protein encoded by the soil-dwelling organism Paenibacillus polymyxa demonstrated that the domain is homologous in function to NEAT domains encoded by pathogenic bacteria. Together, this study provides the first global bioinformatics analysis and phylogenetic evidence that NEAT domains have a strong conservation of function, despite group-specific differences at the amino acid level. These findings will provide information useful for future projects concerning the structure and function of NEAT domains, particularly in pathogens where they have yet to be studied.
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12
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Whiting G, Wheeler JX, Rijpkema S. Identification of peptide sequences as a measure of Anthrax vaccine stability during storage. Hum Vaccin Immunother 2014; 10:1669-81. [PMID: 24637775 PMCID: PMC4185962 DOI: 10.4161/hv.28443] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The UK anthrax vaccine is an alum precipitate of a sterile filtrate of Bacillus anthracis Sterne culture (AVP). An increase in shelf life of AVP from 3 to 5 years prompted us to investigate the in vivo potency and the antigen content of 12 batches with a shelf life of 6.4 to 9.9 years and one bulk with a shelf life of 23.8 years. All batches, except for a 9.4-year-old batch, passed the potency test. Mass spectrometry (MS) and in-gel difference 2-dimensional gel electrophoresis (DIGE) were used to examine antigens of the pellet and supernatant of AVP. The pellet contained proteins with a MW in excess of 15 kDa. DIGE of desorbed proteins from the pellet revealed that with aging, 19 spots showed a significant change in size or intensity, a sign of protein degradation. MS identified 21 proteins including protective antigen (PA), enolase, lethal factor (LF), nucleoside diphosphate kinase, edema factor, and S-layer proteins. Fifteen proteins were detected for the first time including metabolic enzymes, iron binding proteins, and manganese dependent superoxide dismutase (MnSOD). The supernatant contained131 peptide sequences. Peptides representing septum formation inhibitor protein and repeat domain protein were most abundant. Five proteins were shared with the pellet: 2,3,4,5-tetrahydropyridine-6-dicarboxylate N-succinyltransferase, enolase, LF, MnSOD, and PA. The number of peptide sequences increased with age. Peptides from PA and LF appeared once batches exceeded their shelf life by 2 and 4 years, respectively. In conclusion, changes in antigen content resulting from decay or desorption only had a limited effect on in vivo potency of AVP. The presence of PA and LF peptides in the supernatant can inform on the age and stability of AVP.
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Affiliation(s)
- Gail Whiting
- Division of Bacteriology; National Institute for Biological Standards and Control; Hertfordshire, UK
| | - Jun X Wheeler
- Laboratory of Molecular Structure; National Institute for Biological Standards and Control; Hertfordshire, UK
| | - Sjoerd Rijpkema
- Division of Bacteriology; National Institute for Biological Standards and Control; Hertfordshire, UK
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13
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Honsa ES, Owens CP, Goulding CW, Maresso AW. The near-iron transporter (NEAT) domains of the anthrax hemophore IsdX2 require a critical glutamine to extract heme from methemoglobin. J Biol Chem 2013; 288:8479-8490. [PMID: 23364793 DOI: 10.1074/jbc.m112.430009] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Several gram-positive pathogenic bacteria employ near-iron transporter (NEAT) domains to acquire heme from hemoglobin during infection. However, the structural requirements and mechanism of action for NEAT-mediated heme extraction remains unknown. Bacillus anthracis exhibits a rapid growth rate during systemic infection, suggesting that the bacterium expresses efficient iron acquisition systems. To understand how B. anthracis acquires iron from heme sources, which account for 80% of mammalian iron stores, we investigated the properties of the five-NEAT domain hemophore IsdX2. Using a combination of bioinformatics and site-directed mutagenesis, we determined that the heme extraction properties of IsdX2 are dependent on an amino acid with an amide side chain within the 310-helix of the NEAT domain. Additionally, we used a spectroscopic analysis to show that IsdX2 NEAT domains only scavenge heme from methemoglobin (metHb) and that autoxidation of oxyhemoglobin to metHb must occur prior to extraction. We also report the crystal structures of NEAT5 wild type and a Q29T mutant and present surface plasmon resonance data that indicate that the loss of this amide side chain reduces the affinity of the NEAT domain for metHb. We propose a model whereby the amide side chain is first required to drive an interaction with metHb that destabilizes heme, which is subsequently extracted and coordinated in the aliphatic heme-binding environment of the NEAT domain. Because an amino acid with an amide side chain in this position is observed in NEAT domains of several genera of gram-positive pathogenic bacteria, these results suggest that specific targeting of this or nearby residues may be an entry point for inhibitor development aimed at blocking bacterial iron acquisition during infection.
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Affiliation(s)
- Erin S Honsa
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030
| | - Cedric P Owens
- Departments of Molecular Biology and Biochemistry, University of California, Irvine, California 92617
| | - Celia W Goulding
- Departments of Molecular Biology and Biochemistry, University of California, Irvine, California 92617
| | - Anthony W Maresso
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030.
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14
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Abstract
The metal iron is a limiting nutrient for bacteria during infection. Bacillus anthracis, the causative agent of anthrax and a potential weapon of bioterrorism, grows rapidly in mammalian hosts, which suggests that it efficiently attains iron during infection. Recent studies have uncovered both heme (isd) and siderophore-mediated (asb) iron transport pathways in this pathogen. Whereas deletion of the asb genes results in reduced virulence, the loss of three surface components from isd had no effect, thereby leaving open the question of what additional factors in B. anthracis are responsible for iron uptake from the most abundant iron source for mammals, heme. Here, we describe the first functional characterization of bas0520, a gene recently implicated in anthrax disease progression. bas0520 encodes a single near-iron transporter (NEAT) domain and several leucine-rich repeats. The NEAT domain binds heme, despite lacking a stabilizing tyrosine common to the NEAT superfamily of hemoproteins. The NEAT domain also binds hemoglobin and can acquire heme from hemoglobin in solution. Finally, deletion of bas0520 resulted in bacilli unable to grow efficiently on heme or hemoglobin as an iron source and yielded the most significant phenotype relative to that for other putative heme uptake systems, a result that suggests that this protein plays a prominent role in the replication of B. anthracis in hematogenous environments. Thus, we have assigned the name of Hal (heme-acquisition leucine-rich repeat protein) to BAS0520. These studies advance our understanding of heme acquisition by this dangerous pathogen and justify efforts to determine the mechanistic function of this novel protein for vaccine or inhibitor development.
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15
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Ekworomadu MT, Poor CB, Owens CP, Balderas MA, Fabian M, Olson JS, Murphy F, Balkabasi E, Honsa ES, He C, Goulding CW, Maresso AW. Differential function of lip residues in the mechanism and biology of an anthrax hemophore. PLoS Pathog 2012; 8:e1002559. [PMID: 22412371 PMCID: PMC3297588 DOI: 10.1371/journal.ppat.1002559] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 01/16/2012] [Indexed: 11/19/2022] Open
Abstract
To replicate in mammalian hosts, bacterial pathogens must acquire iron. The majority of iron is coordinated to the protoporphyrin ring of heme, which is further bound to hemoglobin. Pathogenic bacteria utilize secreted hemophores to acquire heme from heme sources such as hemoglobin. Bacillus anthracis, the causative agent of anthrax disease, secretes two hemophores, IsdX1 and IsdX2, to acquire heme from host hemoglobin and enhance bacterial replication in iron-starved environments. Both proteins contain NEAr-iron Transporter (NEAT) domains, a conserved protein module that functions in heme acquisition in Gram-positive pathogens. Here, we report the structure of IsdX1, the first of a Gram-positive hemophore, with and without bound heme. Overall, IsdX1 forms an immunoglobin-like fold that contains, similar to other NEAT proteins, a 310-helix near the heme-binding site. Because the mechanistic function of this helix in NEAT proteins is not yet defined, we focused on the contribution of this region to hemophore and NEAT protein activity, both biochemically and biologically in cultured cells. Site-directed mutagenesis of amino acids in and adjacent to the helix identified residues important for heme and hemoglobin association, with some mutations affecting both properties and other mutations affecting only heme stabilization. IsdX1 with mutations that reduced the ability to associate with hemoglobin and bind heme failed to restore the growth of a hemophore-deficient strain of B. anthracis on hemoglobin as the sole iron source. These data indicate that not only is the 310-helix important for NEAT protein biology, but also that the processes of hemoglobin and heme binding can be both separate as well as coupled, the latter function being necessary for maximal heme-scavenging activity. These studies enhance our understanding of NEAT domain and hemophore function and set the stage for structure-based inhibitor design to block NEAT domain interaction with upstream ligands. Pathogenic bacteria need to acquire host iron to replicate during infection. Approximately 80% of mammalian iron is associated with a small molecule termed heme, most of which is bound to circulating hemoglobin and involved in O2 transport in red cells. Bacteria secrete proteins, termed hemophores, to acquire the heme from hemoglobin, a process thought to accelerate delivery of the heme to the bacterial surface for iron import into the cell. The mechanisms by which hemophores extract host heme from hemoglobin are not known. Here, we report that the IsdX1 hemophore from B. anthracis, the causative agent of anthrax disease, uses a conserved structural feature to link hemoglobin association with heme binding and extraction, thereby facilitating bacterial growth in low-iron environments. Such “molecular coupling” suggests that specific inhibition of the hemophore-hemoglobin interaction for this class of proteins may serve as a starting point for new anti-infective therapeutics aimed at short-circuiting iron uptake networks in bacterial pathogens.
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Affiliation(s)
- MarCia T. Ekworomadu
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Catherine B. Poor
- Department of Chemistry, University of Chicago, Chicago, Illinois, United States of America
| | - Cedric P. Owens
- Departments of Molecular Biology and Biochemistry, University of California-Irvine, Irvine, California, United States of America
| | - Miriam A. Balderas
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Marian Fabian
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas, United States of America
| | - John S. Olson
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas, United States of America
| | - Frank Murphy
- Northeastern Collaborative Access Team, Argonne National Laboratory, Argonne, Illinois, United States of America
| | - Erol Balkabasi
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Erin S. Honsa
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Chuan He
- Department of Chemistry, University of Chicago, Chicago, Illinois, United States of America
| | - Celia W. Goulding
- Departments of Molecular Biology and Biochemistry, University of California-Irvine, Irvine, California, United States of America
| | - Anthony W. Maresso
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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16
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Abstract
Although successful iron acquisition by pathogens within a host is a prerequisite for the establishment of infection, surprisingly little is known about the intracellular distribution of iron within bacterial pathogens. We have used a combination of anaerobic native liquid chromatography, inductively coupled plasma mass spectrometry, principal-component analysis, and peptide mass fingerprinting to investigate the cytosolic iron distribution in the pathogen Bacillus anthracis. Our studies identified three of the major iron pools as being associated with the electron transfer protein ferredoxin, the miniferritin Dps2, and the superoxide dismutase (SOD) enzymes SodA1 and SodA2. Although both SOD isozymes were predicted to utilize manganese cofactors, quantification of the metal ions associated with SodA1 and SodA2 in cell extracts established that SodA1 is associated with both manganese and iron, whereas SodA2 is bound exclusively to iron in vivo. These data were confirmed by in vitro assays using recombinant protein preparations, showing that SodA2 is active with an iron cofactor, while SodA1 is cambialistic, i.e., active with manganese or iron. Furthermore, we observe that B. anthracis cells exposed to superoxide stress increase their total iron content more than 2-fold over 60 min, while the manganese and zinc contents are unaffected. Notably, the acquired iron is not localized to the three identified cytosolic iron pools.
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17
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Characterization of the sortase repertoire in Bacillus anthracis. PLoS One 2011; 6:e27411. [PMID: 22076158 PMCID: PMC3208642 DOI: 10.1371/journal.pone.0027411] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Accepted: 10/17/2011] [Indexed: 02/04/2023] Open
Abstract
LPXTG proteins, present in most if not all Gram-positive bacteria, are known to be anchored by sortases to the bacterial peptidoglycan. More than one sortase gene is often encoded in a bacterial species, and each sortase is supposed to specifically anchor given LPXTG proteins, depending of the sequence of the C-terminal cell wall sorting signal (cwss), bearing an LPXTG motif or another recognition sequence. B. anthracis possesses three sortase genes. B. anthracis sortase deleted mutant strains are not affected in their virulence. To determine the sortase repertoires, we developed a genetic screen using the property of the gamma phage to lyse bacteria only when its receptor, GamR, an LPXTG protein, is exposed at the surface. We identified 10 proteins that contain a cell wall sorting signal and are covalently anchored to the peptidoglycan. Some chimeric proteins yielded phage lysis in all sortase mutant strains, suggesting that cwss proteins remained surface accessible in absence of their anchoring sortase, probably as a consequence of membrane localization of yet uncleaved precursor proteins. For definite assignment of the sortase repertoires, we consequently relied on a complementary test, using a biochemical approach, namely immunoblot experiments. The sortase anchoring nine of these proteins has thus been determined. The absence of virulence defect of the sortase mutants could be a consequence of the membrane localization of the cwss proteins.
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18
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Honsa ES, Fabian M, Cardenas AM, Olson JS, Maresso AW. The five near-iron transporter (NEAT) domain anthrax hemophore, IsdX2, scavenges heme from hemoglobin and transfers heme to the surface protein IsdC. J Biol Chem 2011; 286:33652-60. [PMID: 21808055 PMCID: PMC3190864 DOI: 10.1074/jbc.m111.241687] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2011] [Revised: 07/19/2011] [Indexed: 11/06/2022] Open
Abstract
Pathogenic bacteria require iron to replicate inside mammalian hosts. Recent studies indicate that heme acquisition in Gram-positive bacteria is mediated by proteins containing one or more near-iron transporter (NEAT) domains. Bacillus anthracis is a spore-forming, Gram-positive pathogen and the causative agent of anthrax disease. The rapid, extensive, and efficient replication of B. anthracis in host tissues makes this pathogen an excellent model organism for the study of bacterial heme acquisition. B. anthracis secretes two NEAT hemophores, IsdX1 and IsdX2. IsdX1 contains a single NEAT domain, whereas IsdX2 has five, a novel property among hemophores. To understand the functional significance of harboring multiple, non-identical NEAT domains, we purified each individual NEAT domain of IsdX2 as a GST fusion and analyzed the specific function of each domain as it relates to heme acquisition and transport. NEAT domains 1, 3, 4, and 5 all bind heme, with domain 5 having the highest affinity. All NEATs associate with hemoglobin, but only NEAT1 and -5 can extract heme from hemoglobin, seemingly by a specific and active process. NEAT1, -3, and -4 transfer heme to IsdC, a cell wall-anchored anthrax NEAT protein. These results indicate that IsdX2 has all the features required to acquire heme from the host and transport heme to the bacterial cell wall. Additionally, these results suggest that IsdX2 may accelerate iron import rates by acting as a "heme sponge" that enhances B. anthracis replication in iron-starved environments.
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Affiliation(s)
- Erin Sarah Honsa
- From the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030 and
| | - Marian Fabian
- the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77096
| | - Ana Maria Cardenas
- From the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030 and
| | - John S. Olson
- the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77096
| | - Anthony William Maresso
- From the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030 and
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19
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Château A, van Schaik W, Six A, Aucher W, Fouet A. CodY regulation is required for full virulence and heme iron acquisition in Bacillus anthracis. FASEB J 2011; 25:4445-56. [PMID: 21911592 DOI: 10.1096/fj.11-188912] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Capsule and toxin are the major virulence factors of Bacillus anthracis. The B. anthracis pleiotropic regulator CodY activates toxin gene expression by post-translationally regulating the accumulation of the global regulator AtxA. However, the role of CodY on B. anthracis capsulation and virulence of encapsulated strains has been unknown. The role of CodY in B. anthracis virulence was studied in mouse and guinea pig models. Spore outgrowth and dissemination of the vegetative cells was followed in mice by bioluminescent imaging. We also determined the state of capsulation and the iron requirement for growth of the codY mutant. In all models tested, the codY mutant strain was strongly attenuated compared to the wild-type strain and, in mice, also compared to the atxA strain. The disruption of codY did not affect either ex vivo or in vivo capsulation, whereas atxA deletion affected ex vivo capsulation only. The disruption of codY led to a delayed initiation of dissemination but similar kinetics of subsequent spread of the bacilli. The codY mutant cannot grow on heme iron as sole iron source, whereas the parental and complemented strains can. The lack of CodY-mediated transcription weakens virulence by controlling iron acquisition and synthesis of toxin, but without modifying capsulation.
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Affiliation(s)
- Alice Château
- Unité des Toxines et Pathogénie Bactériennes, Laboratoire Pathogénie des Toxi-Infections Bactériennes, Institut Pasteur, Paris, France
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20
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Stauff DL, Skaar EP. Bacillus anthracis HssRS signalling to HrtAB regulates haem resistance during infection. Mol Microbiol 2010; 72:763-78. [PMID: 19400785 DOI: 10.1111/j.1365-2958.2009.06684.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Bacillus anthracis proliferates to high levels within vertebrate tissues during the pathogenesis of anthrax. This growth is facilitated by the acquisition of nutrient iron from host haem. However, haem acquisition can lead to the accumulation of toxic amounts of haem within B. anthracis. Here, we show that B. anthracis resists haem toxicity by sensing haem through the HssRS two-component system, which regulates expression of the haem-detoxifying transporter HrtAB. In addition, we demonstrate that B. anthracis exhibits elevated HssRS function compared with its evolutionary relative Staphylococcus aureus. Elevated haem sensing is likely required by B. anthracis due to the significant haem sensitivity exhibited by members of the genus Bacilli. We also demonstrate that B. anthracis depends on conserved residues within the previously uncharacterized sensing domain of the histidine kinase HssS for HssS function. Finally, we show that the haem- and HssRS-regulated hrtAB promoter is activated in a murine model of anthrax. These results demonstrate the evolutionary conservation of haem sensing among multiple Gram-positive bacteria and begin to provide a mechanistic explanation for the haem resistance of B. anthracis. Further, these data suggest that haem stress is experienced by bacterial pathogens during infection.
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Affiliation(s)
- Devin L Stauff
- Department of Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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21
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Ouattara M, Cunha EB, Li X, Huang YS, Dixon D, Eichenbaum Z. Shr of group A streptococcus is a new type of composite NEAT protein involved in sequestering haem from methaemoglobin. Mol Microbiol 2010; 78:739-56. [PMID: 20807204 DOI: 10.1111/j.1365-2958.2010.07367.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A growing body of evidence suggests that surface or secreted proteins with NEAr Transporter (NEAT) domains play a central role in haem acquisition and trafficking across the cell envelope of Gram-positive bacteria. Group A streptococcus (GAS), a β-haemolytic human pathogen, expresses a NEAT protein, Shr, which binds several haemoproteins and extracellular matrix (ECM) components. Shr is a complex, membrane-anchored protein, with a unique N-terminal domain (NTD) and two NEAT domains separated by a central leucine-rich repeat region. In this study we have carried out an analysis of the functional domains in Shr. We show that Shr obtains haem in solution and furthermore reduces the haem iron; this is the first report of haem reduction by a NEAT protein. More specifically, we demonstrate that both of the constituent NEAT domains of Shr are responsible for binding haem, although they are missing a critical tyrosine residue found in the ligand-binding pocket of other haem-binding NEAT domains. Further investigations show that a previously undescribed region within the Shr NTD interacts with methaemoglobin. Shr NEAT domains, however, do not contribute significantly to the binding of methaemoglobin but mediate binding to the ECM components fibronectin and laminin. A protein fragment containing the NTD plus the first NEAT domain was found to be sufficient to sequester haem directly from methaemoglobin. Correlating these in vitro findings to in vivo biological function, mutants analysis establishes the role of Shr in GAS growth with methaemoglobin as a sole source of iron, and indicates that at least one NEAT domain is necessary for the utilization of methaemoglobin. We suggest that Shr is the prototype of a new group of NEAT composite proteins involved in haem uptake found in pyogenic streptococci and Clostridium novyi.
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Affiliation(s)
- Mahamoudou Ouattara
- Department of Biology,College of Arts and Sciences, Georgia State University, Atlanta, GA 30303, USA
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22
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Overcoming the heme paradox: heme toxicity and tolerance in bacterial pathogens. Infect Immun 2010; 78:4977-89. [PMID: 20679437 DOI: 10.1128/iai.00613-10] [Citation(s) in RCA: 208] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Virtually all bacterial pathogens require iron to infect vertebrates. The most abundant source of iron within vertebrates is in the form of heme as a cofactor of hemoproteins. Many bacterial pathogens have elegant systems dedicated to the acquisition of heme from host hemoproteins. Once internalized, heme is either degraded to release free iron or used intact as a cofactor in catalases, cytochromes, and other bacterial hemoproteins. Paradoxically, the high redox potential of heme makes it a liability, as heme is toxic at high concentrations. Although a variety of mechanisms have been proposed to explain heme toxicity, the mechanisms by which heme kills bacteria are not well understood. Nonetheless, bacteria employ various strategies to protect against and eliminate heme toxicity. Factors involved in heme acquisition and detoxification have been found to contribute to virulence, underscoring the physiological relevance of heme stress during pathogenesis. Herein we describe the current understanding of the mechanisms of heme toxicity and how bacterial pathogens overcome the heme paradox during infection.
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23
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A Bacillus anthracis S-layer homology protein that binds heme and mediates heme delivery to IsdC. J Bacteriol 2010; 192:3503-11. [PMID: 20435727 DOI: 10.1128/jb.00054-10] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The sequestration of iron by mammalian hosts represents a significant obstacle to the establishment of a bacterial infection. In response, pathogenic bacteria have evolved mechanisms to acquire iron from host heme. Bacillus anthracis, the causative agent of anthrax, utilizes secreted hemophores to scavenge heme from host hemoglobin, thereby facilitating iron acquisition from extracellular heme pools and delivery to iron-regulated surface determinant (Isd) proteins covalently attached to the cell wall. However, several Gram-positive pathogens, including B. anthracis, contain genes that encode near iron transporter (NEAT) proteins that are genomically distant from the genetically linked Isd locus. NEAT domains are protein modules that partake in several functions related to heme transport, including binding heme and hemoglobin. This finding raises interesting questions concerning the relative role of these NEAT proteins, relative to hemophores and the Isd system, in iron uptake. Here, we present evidence that a B. anthracis S-layer homology (SLH) protein harboring a NEAT domain binds and directionally transfers heme to the Isd system via the cell wall protein IsdC. This finding suggests that the Isd system can receive heme from multiple inputs and may reflect an adaptation of B. anthracis to changing iron reservoirs during an infection. Understanding the mechanism of heme uptake in pathogenic bacteria is important for the development of novel therapeutics to prevent and treat bacterial infections.
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24
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Daou N, Buisson C, Gohar M, Vidic J, Bierne H, Kallassy M, Lereclus D, Nielsen-LeRoux C. IlsA, a unique surface protein of Bacillus cereus required for iron acquisition from heme, hemoglobin and ferritin. PLoS Pathog 2009; 5:e1000675. [PMID: 19956654 PMCID: PMC2777315 DOI: 10.1371/journal.ppat.1000675] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2009] [Accepted: 10/30/2009] [Indexed: 12/05/2022] Open
Abstract
The human opportunistic pathogen Bacillus cereus belongs to the B. cereus group that includes bacteria with a broad host spectrum. The ability of these bacteria to colonize diverse hosts is reliant on the presence of adaptation factors. Previously, an IVET strategy led to the identification of a novel B. cereus protein (IlsA, Iron-regulated leucine rich surface protein), which is specifically expressed in the insect host or under iron restrictive conditions in vitro. Here, we show that IlsA is localized on the surface of B. cereus and hence has the potential to interact with host proteins. We report that B. cereus uses hemoglobin, heme and ferritin, but not transferrin and lactoferrin. In addition, affinity tests revealed that IlsA interacts with both hemoglobin and ferritin. Furthermore, IlsA directly binds heme probably through the NEAT domain. Inactivation of ilsA drastically decreases the ability of B. cereus to grow in the presence of hemoglobin, heme and ferritin, indicating that IlsA is essential for iron acquisition from these iron sources. In addition, the ilsA mutant displays a reduction in growth and virulence in an insect model. Hence, our results indicate that IlsA is a key factor within a new iron acquisition system, playing an important role in the general virulence strategy adapted by B. cereus to colonize susceptible hosts. Iron is an essential compound for almost all living organisms, taking part in basic cellular homeostasis. Preventing access to iron sources for invading pathogens is one of the defense systems used by hosts to avoid pathogen colonization. To counteract this, pathogens have developed mechanisms to acquire nutrient iron during infection. Bacillus cereus is an opportunistic bacterium able to infect both insects and mammals; thus, it should have systems enabling iron uptake from these hosts. Here we describe, for the first time, a unique surface protein, called IlsA, which is essential for iron uptake from two very different iron binding molecules: ferritin and hemoglobin. IlsA is only produced in iron limited environments. We show that during insect infection, its expression is specific to insect hemocoel (blood), where ferritin is the major iron-binding molecule. Interestingly, the IlsA mutant has reduced survival in in vivo infection and in vitro when heme, hemoglobin and ferritin are the sole iron sources available. Thus, as IlsA is important for iron uptake from the major iron rich molecules in insects and mammals, we suggest that this new iron acquisition system may be a key factor that is evolutionary adapted to infection of such diverse hosts.
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Affiliation(s)
- Nadine Daou
- INRA-UR1249 Génétique Microbienne et Environnement, La Minière, Guyancourt, France
- Laboratoire de Biotechnologie, Université Saint-Joseph, Beyrouth, Lebanon
| | - Christophe Buisson
- INRA-UR1249 Génétique Microbienne et Environnement, La Minière, Guyancourt, France
| | - Michel Gohar
- INRA-UR1249 Génétique Microbienne et Environnement, La Minière, Guyancourt, France
| | - Jasmina Vidic
- INRA-UR892 Unité de Biologie Physico-Chimique des Prions, Virologie et Immunologie Moléculaires, Jouy en Josas, France
| | - Hélène Bierne
- Unité Interaction Bactéries Cellules, Institut Pasteur, INSERM U604 – INRA USC2020, Paris, France
| | - Mireille Kallassy
- Laboratoire de Biotechnologie, Université Saint-Joseph, Beyrouth, Lebanon
| | - Didier Lereclus
- INRA-UR1249 Génétique Microbienne et Environnement, La Minière, Guyancourt, France
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25
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Fabian M, Solomaha E, Olson JS, Maresso AW. Heme transfer to the bacterial cell envelope occurs via a secreted hemophore in the Gram-positive pathogen Bacillus anthracis. J Biol Chem 2009; 284:32138-46. [PMID: 19759022 PMCID: PMC2797284 DOI: 10.1074/jbc.m109.040915] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Revised: 08/28/2009] [Indexed: 11/06/2022] Open
Abstract
To initiate and sustain an infection in mammals, bacterial pathogens must acquire host iron. However, the host's compartmentalization of large amounts of iron in heme, which is bound primarily by hemoglobin in red blood cells, acts as a barrier to bacterial iron assimilation. Bacillus anthracis, the causative agent of the disease anthrax, secretes two NEAT (near iron transporter) proteins, IsdX1 and IsdX2, which scavenge heme from host hemoglobin and promote growth under low iron conditions. The mechanism of heme transfer from these hemophores to the bacterial cell is not known. We present evidence that the heme-bound form of IsdX1 rapidly and directionally transfers heme to IsdC, a NEAT protein covalently attached to the cell wall, as well as to IsdX2. In both cases, the transfer of heme is mediated by a physical association between the donor and recipient. Unlike Staphylococcus aureus, whose NEAT proteins acquire heme from hemoglobin directly at the bacterial surface, B. anthracis secretes IsdX1 to capture heme in the extracellular milieu and relies on NEAT-NEAT interactions to deliver the bound heme to the envelope via IsdC. Understanding the mechanism of NEAT-mediated iron transport into pathogenic Gram-positive bacteria may provide an avenue for the development of therapeutics to combat infection.
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Affiliation(s)
- Marian Fabian
- From the Department of Biochemistry & Cell Biology, Rice University, Houston, Texas 77096
| | - Elena Solomaha
- the Biophysics Core Facility, The University of Chicago, Chicago, Illinois 60637, and
| | - John S. Olson
- From the Department of Biochemistry & Cell Biology, Rice University, Houston, Texas 77096
| | - Anthony W. Maresso
- the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030
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26
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Sela-Abramovich S, Chitlaru T, Gat O, Grosfeld H, Cohen O, Shafferman A. Novel and unique diagnostic biomarkers for Bacillus anthracis infection. Appl Environ Microbiol 2009; 75:6157-67. [PMID: 19648366 PMCID: PMC2753070 DOI: 10.1128/aem.00766-09] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2009] [Accepted: 07/22/2009] [Indexed: 01/28/2023] Open
Abstract
A search for bacterium-specific biomarkers in peripheral blood following infection with Bacillus anthracis was carried out with rabbits, using a battery of specific antibodies generated by DNA vaccination against 10 preselected highly immunogenic bacterial antigens which were identified previously by a genomic/proteomic/serologic screen of the B. anthracis secretome. Detection of infection biomarkers in the circulation of infected rabbits could be achieved only after removal of highly abundant serum proteins by chromatography using a random-ligand affinity column. Besides the toxin component protective antigen, the following three secreted proteins were detected in the circulation of infected animals: the chaperone and protease HtrA (BA3660), an NlpC/P60 endopeptidase (BA1952), and a protein of unknown function harboring two SH3 (Src homology 3) domains (BA0796). The three proteins could be detected in plasma samples from infected animals exhibiting 10(3) to 10(5) CFU/ml blood and also in standard blood cultures at 3 to 6 h post-bacterial inoculation at a bacteremic level as low as 10(3) CFU/ml. Furthermore, the three biomarkers appear to be present only in the secretome of B. anthracis, not in those of the related pathogens B. thuringiensis and B. cereus. To the best of our knowledge, this is the first report of direct detection of B. anthracis-specific proteins, other than the toxin components, in the circulation of infected animals.
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Affiliation(s)
- Sagit Sela-Abramovich
- Department of Biochemistry and Molecular Genetics, Life Science Research Israel Ltd, 2 Ness-Ziona 74100, Israel
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27
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Carlson PE, Carr KA, Janes BK, Anderson EC, Hanna PC. Transcriptional profiling of Bacillus anthracis Sterne (34F2) during iron starvation. PLoS One 2009; 4:e6988. [PMID: 19768119 PMCID: PMC2742718 DOI: 10.1371/journal.pone.0006988] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Accepted: 08/06/2009] [Indexed: 12/31/2022] Open
Abstract
Lack of available iron is one of many environmental challenges that a bacterium encounters during infection and adaptation to iron starvation is important for the pathogen to efficiently replicate within the host. Here we define the transcriptional response of B. anthracis Sterne (34F2) to iron depleted conditions. Genome-wide transcript analysis showed that B. anthracis undergoes considerable changes in gene expression during growth in iron-depleted media, including the regulation of known and candidate virulence factors. Two genes encoding putative internalin proteins were chosen for further study. Deletion of either gene (GBAA0552 or GBAA1340) resulted in attenuation in a murine model of infection. This attenuation was amplified in a double mutant strain. These data define the transcriptional changes induced during growth in low iron conditions and illustrate the potential of this dataset in the identification of putative virulence determinants for future study.
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Affiliation(s)
- Paul E. Carlson
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Katherine A. Carr
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Brian K. Janes
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Erica C. Anderson
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
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28
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Koehler TM. Bacillus anthracis physiology and genetics. Mol Aspects Med 2009; 30:386-96. [PMID: 19654018 DOI: 10.1016/j.mam.2009.07.004] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Accepted: 07/28/2009] [Indexed: 01/11/2023]
Abstract
Bacillus anthracis is a member of the Bacillus cereus group species (also known as the "group 1 bacilli"), a collection of Gram-positive spore-forming soil bacteria that are non-fastidious facultative anaerobes with very similar growth characteristics and natural genetic exchange systems. Despite their close physiology and genetics, the B. cereus group species exhibit certain species-specific phenotypes, some of which are related to pathogenicity. B. anthracis is the etiologic agent of anthrax. Vegetative cells of B. anthracis produce anthrax toxin proteins and a poly-d-glutamic acid capsule during infection of mammalian hosts and when cultured in conditions considered to mimic the host environment. The genes associated with toxin and capsule synthesis are located on the B. anthracis plasmids, pXO1 and pXO2, respectively. Although plasmid content is considered a defining feature of the species, pXO1- and pXO2-like plasmids have been identified in strains that more closely resemble other members of the B. cereus group. The developmental nature of B. anthracis and its pathogenic (mammalian host) and environmental (soil) lifestyles of make it an interesting model for study of niche-specific bacterial gene expression and physiology.
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Affiliation(s)
- Theresa M Koehler
- Department of Microbiology and Molecular Genetics, The University of Texas, Houston Health Science Center, Houston, TX, United States.
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