scholarly journals The Mycobacterium tuberculosis High-Affinity Iron Importer, IrtA, Contains an FAD-Binding Domain

2009 ◽  
Vol 192 (3) ◽  
pp. 861-869 ◽  
Author(s):  
Michelle B. Ryndak ◽  
Shuishu Wang ◽  
Issar Smith ◽  
G. Marcela Rodriguez
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Iron Acquisition ◽  
Binding Domain ◽  
Amino Terminus ◽  
High Affinity ◽  
Iron Deficient ◽  
Essential Nutrient ◽  
Iron Binding Proteins ◽  
Fad Binding

ABSTRACT Iron is an essential nutrient not freely available to microorganisms infecting mammals. To overcome iron deficiency, bacteria have evolved various strategies including the synthesis and secretion of high-affinity iron chelators known as siderophores. The siderophores produced and secreted by Mycobacterium tuberculosis, exomycobactins, compete for iron with host iron-binding proteins and, together with the iron-regulated ABC transporter IrtAB, are required for the survival of M. tuberculosis in iron deficient conditions and for normal replication in macrophages and in mice. This study further characterizes the role of IrtAB in M. tuberculosis iron acquisition. Our results demonstrate a role for IrtAB in iron import and show that the amino terminus domain of IrtA is a flavin-adenine dinucleotide-binding domain essential for iron acquisition. These results suggest a model in which the amino terminus of IrtA functions to couple iron transport and assimilation.

scholarly journals Reductive Iron Assimilation and Intracellular Siderophores Assist Extracellular Siderophore-Driven Iron Homeostasis and Virulence

2014 ◽  
Vol 27 (8) ◽  
pp. 793-808 ◽  
Author(s):  
Bradford J. Condon ◽  
Shinichi Oide ◽  
Donna M. Gibson ◽  
Stuart B. Krasnoff ◽  
B. Gillian Turgeon
Keyword(s):  
Iron Homeostasis ◽  
Iron Acquisition ◽  
Wild Type ◽  
Peptide Synthetases ◽  
Asexual Sporulation ◽  
High Affinity ◽  
Iron Assimilation ◽  
Genes Encoding ◽  
Essential Nutrient

Iron is an essential nutrient and prudent iron acquisition and management are key traits of a successful pathogen. Fungi use nonribosomally synthesized secreted iron chelators (siderophores) or reductive iron assimilation (RIA) mechanisms to acquire iron in a high affinity manner. Previous studies with the maize pathogen Cochliobolus heterostrophus identified two genes, NPS2 and NPS6, encoding different nonribosomal peptide synthetases responsible for biosynthesis of intra- and extracellular siderophores, respectively. Deletion of NPS6 results in loss of extracellular siderophore biosynthesis, attenuated virulence, hypersensitivity to oxidative and iron-depletion stress, and reduced asexual sporulation, while nps2 mutants are phenotypically wild type in all of these traits but defective in sexual spore development when NPS2 is missing from both mating partners. Here, it is reported that nps2nps6 mutants have more severe phenotypes than both nps2 and nps6 single mutants. In contrast, mutants lacking the FTR1 or FET3 genes encoding the permease and ferroxidase components, respectively, of the alternate RIA system, are like wild type in all of the above phenotypes. However, without supplemental iron, combinatorial nps6ftr1 and nps2nps6ftr1 mutants are less virulent, are reduced in growth, and are less able to combat oxidative stress and to sporulate asexually, compared with nps6 mutants alone. These findings demonstrate that, while the role of RIA in metabolism and virulence is overshadowed by that of extracellular siderophores as a high-affinity iron acquisition mechanism in C. heterostrophus, it functions as a critical backup for the fungus.

scholarly journals PPE Surface Proteins Are Required for Heme Utilization by Mycobacterium tuberculosis

mBio ◽  
2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Avishek Mitra ◽  
Alexander Speer ◽  
Kan Lin ◽  
Sabine Ehrt ◽  
Michael Niederweis
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Human Body ◽  
Iron Acquisition ◽  
Bacterial Pathogens ◽  
Surface Proteins ◽  
Resonance Spectroscopy ◽  
Heme Uptake ◽  
Human Host ◽  
Essential Nutrient ◽  
Growth Experiments

ABSTRACT Iron is essential for replication of Mycobacterium tuberculosis, but iron is efficiently sequestered in the human host during infection. Heme constitutes the largest iron reservoir in the human body and is utilized by many bacterial pathogens as an iron source. While heme acquisition is well studied in other bacterial pathogens, little is known in M. tuberculosis. To identify proteins involved in heme utilization by M. tuberculosis, a transposon mutant library was screened for resistance to the toxic heme analog gallium(III)-porphyrin (Ga-PIX). Inactivation of the ppe36, ppe62, and rv0265c genes resulted in resistance to Ga-PIX. Growth experiments using isogenic M. tuberculosis deletion mutants showed that PPE36 is essential for heme utilization by M. tuberculosis, while the functions of PPE62 and Rv0265c are partially redundant. None of the genes restored growth of the heterologous M. tuberculosis mutants, indicating that the proteins encoded by the genes have separate functions. PPE36, PPE62, and Rv0265c bind heme as shown by surface plasmon resonance spectroscopy and are associated with membranes. Both PPE36 and PPE62 proteins are cell surface accessible, while the Rv0265c protein is probably located in the periplasm. PPE36 and PPE62 are, to our knowledge, the first proline-proline-glutamate (PPE) proteins of M. tuberculosis that bind small molecules and are involved in nutrient acquisition. The absence of a virulence defect of the ppe36 deletion mutant indicates that the different iron acquisition pathways of M. tuberculosis may substitute for each other during growth and persistence in mice. The emerging model of heme utilization by M. tuberculosis as derived from this study is substantially different from those of other bacteria. IMPORTANCE Tuberculosis is caused by Mycobacterium tuberculosis and is a devastating disease affecting eight million people each year. Iron is an essential nutrient for replication of M. tuberculosis in the human host. More than 70% of iron in the human body is bound in heme. Not surprisingly, many bacterial pathogens, including M. tuberculosis, are able to acquire iron from heme. However, the mechanism of heme uptake by M. tuberculosis is poorly understood. We have identified two novel surface proteins that bind heme and are required for heme utilization by M. tuberculosis. These findings constitute a major advancement of our understanding of iron acquisition by M. tuberculosis and show that M. tuberculosis has evolved heme uptake systems different from the paradigms established by other bacteria. IMPORTANCE Tuberculosis is caused by Mycobacterium tuberculosis and is a devastating disease affecting eight million people each year. Iron is an essential nutrient for replication of M. tuberculosis in the human host. More than 70% of iron in the human body is bound in heme. Not surprisingly, many bacterial pathogens, including M. tuberculosis, are able to acquire iron from heme. However, the mechanism of heme uptake by M. tuberculosis is poorly understood. We have identified two novel surface proteins that bind heme and are required for heme utilization by M. tuberculosis. These findings constitute a major advancement of our understanding of iron acquisition by M. tuberculosis and show that M. tuberculosis has evolved heme uptake systems different from the paradigms established by other bacteria.

scholarly journals Transferrin and Lactoferrin – Human Iron Sources for Enterococci

2017 ◽  
Vol 66 (4) ◽  
pp. 419-425 ◽  
Author(s):  
Paweł Lisiecki
Keyword(s):  
Iron Reduction ◽  
Protein Complexes ◽  
Iron Acquisition ◽  
Polyacrylamide Gel Electrophoresis ◽  
Binding Activity ◽  
Host Protein ◽  
Iron Release ◽  
Reduction Of Iron ◽  
Iron Deficient ◽  
Iron Binding Proteins

To overcome limitations in iron acquisition, enterococci have evolved a number of mechanisms to scavenge iron from the host iron-binding proteins – transferrin (TR) and lactoferrin (LF). The aim of this study was to demonstrate the mechanisms by which enterococci utilize human TR and LF bound iron. The study included two strains of Enterococcus faecalis grown in iron-deficient and iron-excess media respectively. The binding activity of both proteins was monitored using proteins labelled with 125I. The uptake of iron by enterococci was determined using 59Fe labelled proteins. Reduction of iron bound to TR and LF was assayed with ferrozine. The proteolytic cleavage of TR and LF was visualized by SDS-polyacrylamide gel electrophoresis. The siderophore activity was measured with chrome azurol S. The study revealed that enterococci use several ways to acquire iron from TR and LF, such as iron chelating siderophores, iron reduction – facilitated iron release, protein degradation – promoted iron release, and receptor mediated capture of the iron-host protein complexes. The broad spectrum of iron acquisition mechanisms used by enterococci may play a significant role in the colonization of the human body and the resulting pathogenicity.

scholarly journals Examining the role of Rv2895c (ViuB) in iron acquisition in Mycobacterium tuberculosis

Tuberculosis ◽  
2012 ◽  
Vol 92 (1) ◽  
pp. 60-62 ◽  
Author(s):  
Sujatha M. Santhanagopalan ◽  
G. Marcela Rodriguez
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Iron Acquisition

scholarly journals Norepinephrine Mediates Acquisition of Transferrin-Iron in Bordetella bronchiseptica

2008 ◽  
Vol 190 (11) ◽  
pp. 3940-3947 ◽  
Author(s):  
Mark T. Anderson ◽  
Sandra K. Armstrong
Keyword(s):  
Iron Transport ◽  
Iron Acquisition ◽  
Receptor Gene ◽  
Growth Stimulation ◽  
Bordetella Bronchiseptica ◽  
Carrier Protein ◽  
Host Environment ◽  
High Affinity ◽  
Essential Nutrient ◽  
Transport Receptor

ABSTRACT Previous research demonstrated that the sympathoadrenal catecholamine norepinephrine could promote the growth of Bordetella bronchiseptica in iron-restricted medium containing serum. In this study, norepinephrine was demonstrated to stimulate growth of this organism in the presence of partially iron-saturated transferrin but not lactoferrin. Although norepinephrine is known to induce transcription of the Bordetella bfeA enterobactin catechol xenosiderophore receptor gene, neither a bfeA mutant nor a bfeR regulator mutant was defective in growth responsiveness to norepinephrine. However, growth of a tonB mutant strain was not enhanced by norepinephrine, indicating that the response to this catecholamine was the result of high-affinity outer membrane transport. The B. bronchiseptica genome encodes a total of 19 known and predicted iron transport receptor genes, none of which, when mutated individually, were found to confer a defect in norepinephrine-mediated growth stimulation in the presence of transferrin. Labeling experiments demonstrated a TonB-dependent increase in cell-associated iron levels when bacteria grown in the presence of 55Fe-transferrin were exposed to norepinephrine. In addition, TonB was required for maximum levels of cell-associated norepinephrine. Together, these results demonstrate that norepinephrine facilitates B. bronchiseptica iron acquisition from the iron carrier protein transferrin and this process may represent a mechanism by which some bacterial pathogens obtain this essential nutrient in the host environment.

scholarly journals Exochelins of Mycobacterium tuberculosis remove iron from human iron-binding proteins and donate iron to mycobactins in the M. tuberculosis cell wall.

1996 ◽  
Vol 183 (4) ◽  
pp. 1527-1532 ◽  
Author(s):  
J Gobin ◽  
M A Horwitz
Keyword(s):  
Cell Wall ◽  
Mycobacterium Tuberculosis ◽  
Binding Proteins ◽  
Core Structure ◽  
Water Soluble ◽  
Side Chain ◽  
Iron Binding ◽  
Alkyl Side Chain ◽  
High Affinity ◽  
Iron Binding Proteins

To multiply and cause disease in the host, Mycobacterium tuberculosis must acquire iron from the extracellular environment at sites of replication. To do so, the bacterium releases high-affinity iron-binding siderophores called exochelins. In previous studies, we have described the purification and characterization of the exochelin family of molecules. These molecules share a common core structure with another type of high-affinity iron-binding molecule located in the cell wall of M. tuberculosis: the mycobactins. The water-soluble exochelins differ from each other and from water insoluble mycobactins in polarity, which is dependent primarily upon the length and modifications of an alkyl side chain. In this study, we have investigated the capacity of purified exochelins to remove iron from host high-affinity iron-binding molecules, and to transfer iron to mycobactins. Purified desferri-exochelins rapidly removed iron from human transferrin, whether it was 95 or 40% iron saturated, its approximate percent saturation in human serum, and from human lactoferrin. Desferri-exochelins also removed iron, but at a slower rate, from the iron storage protein ferritin. Purified ferri-exochelins, but not iron transferrin, transferred iron to desferri-mycobactins in the cell wall of live bacteria. To explore the possibility that the transfer iron from exochelins to mycobactins was influenced by their polarity, we investigated the influence of polarity on the iron affinity of exochelins. Exochelins of different polarity exchanged iron equally with each other. This study supports the concept that exochelins acquire iron for M. tuberculosis by removing this element from host iron-binding proteins and transferring it to desferri-mycobactins in the cell wall of the bacterium. The finding that ferri-exochelins but not iron transferrin transfer iron to mycobactins in the cell wall underscores the importance of exochelins in iron acquisition. This study also shows that the variable alkyl side chain on the core structure of exochelins and mycobactins, the principal determinant of their polarity, has little or no influence on their iron affinity.

The role of lactoferrin binding protein B in mediating protection against human lactoferricin1This article is part of a Special Issue entitled Lactoferrin and has undergone the Journal's usual peer review process.

2012 ◽  
Vol 90 (3) ◽  
pp. 417-423 ◽  
Author(s):  
Ari Morgenthau ◽  
Margaret Livingstone ◽  
Paul Adamiak ◽  
Anthony B. Schryvers
Keyword(s):  
Peer Review Process ◽  
Binding Protein ◽  
Iron Acquisition ◽  
Protein A ◽  
Human Lactoferrin ◽  
Cationic Antimicrobial Peptide ◽  
Iron Source ◽  
Iron Deficient ◽  
Protein B

Bacteria that inhabit the mucosal surfaces of the respiratory and genitourinary tracts of mammals encounter an iron-deficient environment because of iron sequestration by the host iron-binding proteins transferrin and lactoferrin. Lactoferrin is also present in high concentrations at sites of inflammation where the cationic, antimicrobial peptide lactoferricin is produced by proteolysis of lactoferrin. Several Gram-negative pathogens express a lactoferrin receptor that enables the bacteria to use lactoferrin as an iron source. The receptor is composed of an integral membrane protein, lactoferrin binding protein A (LbpA), and a membrane-bound lipoprotein, lactoferrin binding protein B (LbpB). LbpA is essential for growth with lactoferrin as the sole iron source, whereas the role of LbpB in iron acquisition is not yet known. In this study, we demonstrate that LbpB from 2 different species is capable of providing protection against the killing activity of a human lactoferrin-derived peptide. We investigated the prevalence of lactoferrin receptors in bacteria and examined their sequence diversity. We propose that the protection against the cationic antimicrobial human lactoferrin-derived peptide is associated with clusters of negatively charged amino acids in the C-terminal lobe of LbpB that is a common feature of this protein.

scholarly journals Strategies for acquiring the phospholipid metabolite inositol in pathogenic bacteria, fungi and protozoa: making it and taking it

Microbiology ◽  
2009 ◽  
Vol 155 (5) ◽  
pp. 1386-1396 ◽  
Author(s):  
Todd B. Reynolds
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Candida Albicans ◽  
Trypanosoma Brucei ◽  
Pathogenic Bacteria ◽  
De Novo ◽  
The Other ◽  
Inositol Monophosphatase ◽  
Essential Nutrient ◽  
Phosphate Synthase

myo-Inositol (inositol) is an essential nutrient that is used for building phosphatidylinositol and its derivatives in eukaryotes and even in some eubacteria such as the mycobacteria. As a consequence, fungal, protozoan and mycobacterial pathogens must be able to acquire inositol in order to proliferate and cause infection in their hosts. There are two primary mechanisms for acquiring inositol. One is to synthesize inositol from glucose 6-phosphate using two sequentially acting enzymes: inositol-3-phosphate synthase (Ino1p) converts glucose 6-phosphate to inositol 3-phosphate, and then inositol monophosphatase (IMPase) dephosphorylates inositol 3-phosphate to generate inositol. The other mechanism is to import inositol from the environment via inositol transporters. Inositol is readily abundant in the bloodstream of mammalian hosts, providing a source from which many pathogens could potentially import inositol. However, despite this abundance of inositol in the host, some pathogens such as the bacterium Mycobacterium tuberculosis and the protist parasite Trypanosoma brucei must be able to make inositol de novo in order to cause disease (M. tuberculosis) or even grow (T. brucei). Other pathogens such as the fungus Candida albicans are equally adept at causing disease by importing inositol or by making it de novo. The role of inositol acquisition in the biology and pathogenesis of the parasite Leishmania and the fungus Cryptococcus are being explored as well. The specific strategies used by these pathogens to acquire inositol while in the host are discussed in relation to each pathogen's unique metabolic requirements.

scholarly journals Identification and Analysis of “Extended −10” Promoters from Mycobacteria

1998 ◽  
Vol 180 (9) ◽  
pp. 2568-2573 ◽  
Author(s):  
Murali D. Bashyam ◽  
Anil K. Tyagi
Keyword(s):  
Escherichia Coli ◽  
Mycobacterium Tuberculosis ◽  
Sigma Factor ◽  
Mycobacterium Smegmatis ◽  
Important Determinant ◽  
Comparative Assessment ◽  
Binding Domain ◽  
Site Specific ◽  
E Coli

ABSTRACT Earlier studies from our laboratory on randomly isolated transcriptional signals of mycobacteria had revealed that the −10 region of mycobacterial promoters and the corresponding binding domain in the major sigma factor are highly similar to their Escherichia coli counterparts. In contrast, the sequences in −35 regions of mycobacterial promoters and the corresponding binding domain in the major sigma factor are vastly different from their E. colicounterparts (M. D. Bashyam, D. Kaushal, S. K. Dasgupta, and A. K. Tyagi, J. Bacteriol. 178:4847–4853, 1996). We have now analyzed the role of the TGN motif present immediately upstream of the −10 region of mycobacterial promoters. Sequence analysis and site-specific mutagenesis of a Mycobacterium tuberculosispromoter and a Mycobacterium smegmatis promoter reveal that the TGN motif is an important determinant of transcriptional strength in mycobacteria. We show that mutation in the TGN motif can drastically reduce the transcriptional strength of a mycobacterial promoter. The influence of the TGN motif on transcriptional strength is also modulated by the sequences in the −35 region. Comparative assessment of these extended −10 promoters in mycobacteria and E. coli suggests that functioning of the TGN motif in promoters of these two species is similar.

scholarly journals Contribution of Active Iron Uptake toAcinetobacter baumanniiPathogenicity

2019 ◽  
Vol 87 (4) ◽  
Author(s):  
Federica Runci ◽  
Valentina Gentile ◽  
Emanuela Frangipani ◽  
Giordano Rampioni ◽  
Livia Leoni ◽  
...  
Keyword(s):  
Human Serum ◽  
Iron Uptake ◽  
Iron Acquisition ◽  
Human Infection ◽  
Intracellular Iron ◽  
Content Type ◽  
Promising Target ◽  
Essential Nutrient

ABSTRACTAcinetobacter baumanniiis an important nosocomial pathogen. Mechanisms that allowA. baumanniito cause human infection are still poorly understood. Iron is an essential nutrient for bacterial growthin vivo, and the multiplicity of iron uptake systems inA. baumanniisuggests that iron acquisition contributes to the ability ofA. baumanniito cause infection. In Gram-negative bacteria, active transport of ferrisiderophores and heme relies on the conserved TonB-ExbB-ExbD energy-transducing complex, while active uptake of ferrous iron is mediated by the Feo system. TheA. baumanniigenome invariably contains threetonBgenes (tonB1,tonB2, andtonB3), whose role in iron uptake is poorly understood. Here, we generatedA. baumanniimutants with knockout mutations in thefeoand/ortonBgene. We report thattonB3is essential forA. baumanniigrowth under iron-limiting conditions, whereastonB1,tonB2, andfeoBappear to be dispensable for ferric iron uptake.tonB3deletion resulted in reduced intracellular iron content despite siderophore overproduction, supporting a key role of TonB3 in iron uptake. In contrast to the case fortonB1andtonB2, the promoters oftonB3andfeocontain functional Fur boxes and are upregulated in iron-poor media. Both TonB3 and Feo systems are required for growth in complement-free human serum and contribute to resistance to the bactericidal activity of normal human serum, but only TonB3 appears to be essential for virulence in insect and mouse models of infection. Our findings highlight a central role of the TonB3 system forA. baumanniipathogenicity. Hence, TonB3 represents a promising target for novel antibacterial therapies and for the generation of attenuated vaccine strains.

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