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Pogoutse AK, Moraes TF. Iron acquisition through the bacterial transferrin receptor. Crit Rev Biochem Mol Biol 2017; 52:314-326. [PMID: 28276700 DOI: 10.1080/10409238.2017.1293606] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Transferrin is one of the sources of iron that is most readily available to colonizing and invading pathogens. In this review, we look at iron uptake by the bacterial transferrin receptor that is found in the families Neisseriaceae, Pasteurellaceae and Moraxellaceae. This bipartite receptor consists of the TonB-dependent transporter, TbpA, and the surface lipoprotein, TbpB. In the past three decades, major advancements have been made in our understanding of the mechanism through which the Tbps take up iron. We summarize these findings and discuss how they relate to the diversity and specificity of the transferrin receptor. We also outline several of the remaining unanswered questions about iron uptake via the bacterial transferrin receptor and suggest directions for future research.
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Affiliation(s)
| | - Trevor F Moraes
- a Department of Biochemistry , University of Toronto , Toronto , Canada
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2
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Brooks CL, Arutyunova E, Lemieux MJ. The structure of lactoferrin-binding protein B from Neisseria meningitidis suggests roles in iron acquisition and neutralization of host defences. Acta Crystallogr F Struct Biol Commun 2014; 70:1312-7. [PMID: 25286931 PMCID: PMC4188071 DOI: 10.1107/s2053230x14019372] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 08/27/2014] [Indexed: 11/10/2022] Open
Abstract
Pathogens have evolved a range of mechanisms to acquire iron from the host during infection. Several Gram-negative pathogens including members of the genera Neisseria and Moraxella have evolved two-component systems that can extract iron from the host glycoproteins lactoferrin and transferrin. The homologous iron-transport systems consist of a membrane-bound transporter and an accessory lipoprotein. While the mechanism behind iron acquisition from transferrin is well understood, relatively little is known regarding how iron is extracted from lactoferrin. Here, the crystal structure of the N-terminal domain (N-lobe) of the accessory lipoprotein lactoferrin-binding protein B (LbpB) from the pathogen Neisseria meningitidis is reported. The structure is highly homologous to the previously determined structures of the accessory lipoprotein transferrin-binding protein B (TbpB) and LbpB from the bovine pathogen Moraxella bovis. Docking the LbpB structure with lactoferrin reveals extensive binding interactions with the N1 subdomain of lactoferrin. The nature of the interaction precludes apolactoferrin from binding LbpB, ensuring the specificity of iron-loaded lactoferrin. The specificity of LbpB safeguards proper delivery of iron-bound lactoferrin to the transporter lactoferrin-binding protein A (LbpA). The structure also reveals a possible secondary role for LbpB in protecting the bacteria from host defences. Following proteolytic digestion of lactoferrin, a cationic peptide derived from the N-terminus is released. This peptide, called lactoferricin, exhibits potent antimicrobial effects. The docked model of LbpB with lactoferrin reveals that LbpB interacts extensively with the N-terminal lactoferricin region. This may provide a venue for preventing the production of the peptide by proteolysis, or directly sequestering the peptide, protecting the bacteria from the toxic effects of lactoferricin.
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Affiliation(s)
- Cory L. Brooks
- Department of Chemistry, California State University Fresno, Fresno, CA 93710, USA
| | - Elena Arutyunova
- Department of Biochemistry, University of Alberta, Edmonton, AB T6J 2H7, Canada
| | - M. Joanne Lemieux
- Department of Biochemistry, University of Alberta, Edmonton, AB T6J 2H7, Canada
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3
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Sun Y, Zhu Z, Wang R, Sun Y, Xu T. Miiuy croaker transferrin gene and evidence for positive selection events reveal different evolutionary patterns. PLoS One 2012; 7:e43936. [PMID: 22957037 PMCID: PMC3434209 DOI: 10.1371/journal.pone.0043936] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2012] [Accepted: 07/26/2012] [Indexed: 01/12/2023] Open
Abstract
Transferrin (TF) is a protein that plays a central role in iron metabolism. This protein is associated with the innate immune system, which is responsible for disease defense responses after bacterial infection. The clear link between TF and the immune defense mechanism has led researchers to consider TF as a candidate gene for disease resistance. In this study, the Miichthys miiuy (miiuy croaker) TF gene (MIMI-TF) was cloned and characterized. The gene structure consisted of a coding region of 2070 nucleotides divided into 17 exons, as well as a non-coding region that included 16 introns and spans 6757 nucleotides. The deduced MIMI-TF protein consisted of 689 amino acids that comprised a signal peptide and two lobes (N- and C-lobes). MIMI-TF expression was significantly up-regulated after infection with Vibrio anguillarum. A series of model tests implemented in the CODEML program showed that TF underwent a complex evolutionary process. Branch-site models revealed that vertebrate TF was vastly different from that of invertebrates, and that the TF of the ancestors of aquatic and terrestrial organisms underwent different selection pressures. The site models detected 10 positively selected sites in extant TF genes. One site was located in the cleft between the N1 and N2 domains and was expected to affect the capability of TF to bind to or release iron indirectly. In addition, eight sites were found near the TF exterior. Two of these sites, which could have evolved from the competition for iron between pathogenic bacteria and TF, were located in potential pathogen-binding domains. Our results could be used to further investigate the function of TF and the selective mechanisms involved.
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Affiliation(s)
- Yueyan Sun
- Laboratory for Marine Living Resources and Molecular Engineering, College of Marine Science, Zhejiang Ocean University, Zhoushan, China
| | - Zhihuang Zhu
- Laboratory for Marine Living Resources and Molecular Engineering, College of Marine Science, Zhejiang Ocean University, Zhoushan, China
| | - Rixin Wang
- Laboratory for Marine Living Resources and Molecular Engineering, College of Marine Science, Zhejiang Ocean University, Zhoushan, China
| | - Yuena Sun
- Laboratory for Marine Living Resources and Molecular Engineering, College of Marine Science, Zhejiang Ocean University, Zhoushan, China
| | - Tianjun Xu
- Laboratory for Marine Living Resources and Molecular Engineering, College of Marine Science, Zhejiang Ocean University, Zhoushan, China
- * E-mail:
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Silva LP, Yu R, Calmettes C, Yang X, Moraes TF, Schryvers AB, Schriemer DC. Conserved interaction between transferrin and transferrin-binding proteins from porcine pathogens. J Biol Chem 2011; 286:21353-60. [PMID: 21487007 DOI: 10.1074/jbc.m111.226449] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gram-negative porcine pathogens from the Pasteurellaceae family possess a surface receptor complex capable of acquiring iron from porcine transferrin (pTf). This receptor consists of transferrin-binding protein A (TbpA), a transmembrane iron transporter, and TbpB, a surface-exposed lipoprotein. Questions remain as to how the receptor complex engages pTf in such a way that iron is positioned for release, and whether divergent strains present distinct recognition sites on Tf. In this study, the TbpB-pTf interface was mapped using a combination of mass shift analysis and molecular docking simulations, localizing binding uniquely to the pTf C lobe for multiple divergent strains of Actinobacillus plueropneumoniae and suis. The interface was further characterized and validated with site-directed mutagenesis. Although targeting a common lobe, variants differ in preference for the two sublobes comprising the iron coordination site. Sublobes C1 and C2 participate in high affinity binding, but sublobe C1 contributes in a minor fashion to the overall affinity. Further, the TbpB-pTf complex does not release iron independent of other mediators, based on competitive iron binding studies. Together, our findings support a model whereby TbpB efficiently captures and presents iron-loaded pTf to other elements of the uptake pathway, even under low iron conditions.
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Affiliation(s)
- Leslie P Silva
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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5
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Ling JML, Shima CH, Schriemer DC, Schryvers AB. Delineating the regions of human transferrin involved in interactions with transferrin binding protein B from Neisseria meningitidis. Mol Microbiol 2010; 77:1301-14. [DOI: 10.1111/j.1365-2958.2010.07289.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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6
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Liang GM, Jiang XP. Positive selection drives lactoferrin evolution in mammals. Genetica 2010; 138:757-62. [PMID: 20401683 DOI: 10.1007/s10709-010-9456-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2009] [Accepted: 04/06/2010] [Indexed: 01/05/2023]
Abstract
Lactoferrin (LF) is a member of the transferrin family that is abundantly expressed and secreted by glandular epithelial cells. The biological functions of LF involve in iron homeostasis regulation of the body and antibacterial activity. Previous studies demonstrated that it had a high cationic N-terminal domain that could interact with glycosaminoglycans, lipopolysaccharides and the bacterial virulence protein. Two anti-microbial peptides, lactoferricin (LFcin) and lactoferrampin (LFampin), were also isolated and identified in N-terminal of LF. Although the antibacterial mechanism was carefully studied, little was known about the molecular evolution of LF. In this study, we estimated the nonsynonymous-to-synonymous substitution ratios ( ) per site using maximum likelihood method to analyze the LF evolution. The results of omega > 1 and five identified positive selection sites of amino acid suggested that the evolution of LF gene was characterized by positive selection. Further study found that the positive selection sites were either located in the LF-bacteria binding region or the peptides of LFcin and LFampin, indicating that the selection pressure was related to LF-bacteria interaction. The identification of these sites may contribute to the mechanism of bacteria-LF interaction.
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Affiliation(s)
- Guo Ming Liang
- Animal Science Department, Huazhong Agricultural University, Wuhan, People's Republic of China
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7
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Beddek AJ, Schryvers AB. The lactoferrin receptor complex in gram negative bacteria. Biometals 2010; 23:377-86. [DOI: 10.1007/s10534-010-9299-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Accepted: 01/29/2010] [Indexed: 10/19/2022]
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Moraes TF, Yu RH, Strynadka NCJ, Schryvers AB. Insights into the bacterial transferrin receptor: the structure of transferrin-binding protein B from Actinobacillus pleuropneumoniae. Mol Cell 2009; 35:523-33. [PMID: 19716795 DOI: 10.1016/j.molcel.2009.06.029] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 05/09/2009] [Accepted: 06/11/2009] [Indexed: 11/17/2022]
Abstract
Pathogenic bacteria from the Neisseriaceae and Pasteurellacea families acquire iron directly from the host iron-binding glycoprotein, transferrin (Tf), in a process mediated by surface receptor proteins that directly bind host Tf, extract the iron, and transport it across the outer membrane. The bacterial Tf receptor is comprised of a surface exposed lipoprotein, Tf-binding protein B (TbpB), and an integral outer-membrane protein, Tf-binding protein A (TbpA), both of which are essential for survival in the host. In this study, we report the 1.98 A resolution structure of TbpB from the porcine pathogen Actinobacillus pleuropneumoniae, providing insights into the mechanism of Tf binding and the role of TbpB. A model for the complex of TbpB bound to Tf is proposed. Mutation of a single surface-exposed Phe residue on TbpB within the predicted interface completely abolishes binding to Tf, suggesting that the TbpB N lobe comprises the sole high-affinity binding region for Tf.
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Affiliation(s)
- Trevor F Moraes
- Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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9
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Jurecka P, Irnazarow I, Westphal AH, Forlenza M, Arts JAJ, Savelkoul HFJ, Wiegertjes GF. Allelic discrimination, three-dimensional analysis and gene expression of multiple transferrin alleles of common carp (Cyprinus carpio L.). FISH & SHELLFISH IMMUNOLOGY 2009; 26:573-581. [PMID: 18824109 DOI: 10.1016/j.fsi.2008.08.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Revised: 08/22/2008] [Accepted: 08/22/2008] [Indexed: 05/26/2023]
Abstract
We cloned and sequenced four different transferrin (Tf) alleles (C, D, F and G) of European common carp (Cyprinus carpio carpio L.) and studied allelic diversity with respect to differences in sequence, constitutive transcription and three-dimensional structure. Most of the disulfide bonds were conserved between human and carp Tf, and modeling confirmed the overall conservation of the three-dimensional structure of carp Tf. While the iron-binding sites in the C-lobe of carp Tf were completely conserved, in the N-lobe the majority of iron-coordinating residues were not conserved. This may have a serious impact on the ability of carp Tf to bind iron with both the C- and N-lobe. In contrast to human Tf, we could not detect potential N-glycosylation sites in carp Tf, which does not seem to be a glycoprotein. Comparison of the cDNA of the four Tf alleles of carp indicated 21 polymorphic sites of which 13 resulted in non-synonymous changes. Allelic diversity did not seem to influence the overall conservation of carp Tf. Neither the iron binding sites nor the receptor binding of carp Tf seemed influenced by allelic diversity. Possibly, interaction with pathogen-associated receptors for Tf could be influenced by allelic diversity. Basal gene expression of Tf alleles D and G was especially high in carp liver. Although we could detect a higher transcription level of allele D than of Tf allele G in head kidney, thymus and spleen, the differences seem minor with respect to the very high transcription level in liver. Preliminary results with Tf-typed serum suggest a difference in the ability of Tf alleles D and G to modulate LPS-induced NO production in carp macrophages.
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Affiliation(s)
- Patrycja Jurecka
- Institute of Ichthyobiology and Aquaculture, Polish Academy of Sciences, Gołysz, 43-520 Chybie, Poland
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10
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DeRocco AJ, Yost-Daljev MK, Kenney CD, Cornelissen CN. Kinetic analysis of ligand interaction with the gonococcal transferrin-iron acquisition system. Biometals 2008; 22:439-51. [PMID: 19048191 DOI: 10.1007/s10534-008-9179-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Accepted: 11/07/2008] [Indexed: 11/30/2022]
Abstract
The transferrin iron acquisition system of Neisseria gonorrhoeae consists of two dissimilar transferrin binding proteins (Tbp) A and B. TbpA is a TonB dependent transporter while TbpB is a lipoprotein that makes iron acquisition from transferrin (Tf) more efficient. In an attempt to further define the individual roles of these receptors in the process of Tf-iron acquisition, the kinetics of the receptor proteins in regards to ligand association and dissociation were evaluated. Tf association with TbpB was rapid as compared to TbpA. Tf dissociation from the wild-type receptor occurred in a biphasic manner; an initial rapid release was followed by a slower dissociation over time. Both TbpA and TbpB demonstrated a two-phase release pattern; however, TbpA required both TonB and TbpB for efficient Tf dissociation from the cell surface. The roles of TbpA and TbpB in Tf dissociation were further examined, utilizing previously created HA fusion proteins. Using a Tf-utilization deficient TbpA-HA mutant, we concluded that the slower rate of ligand dissociation demonstrated by the wild-type transporter was a function of successful iron internalization. Insertion into the C-terminus of TbpB decreased the rate of Tf dissociation, while insertion into the N-terminus had no effect on this process. From these studies, we propose that TbpA and TbpB function synergistically during the process of Tf iron acquisition and that TbpB makes the process of Tf-iron acquisition more efficient at least in part by affecting association and dissociation of Tf from the cell surface.
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Affiliation(s)
- Amanda J DeRocco
- Department of Microbiology, Virginia Commonwealth University Medical Center, PO Box 980678, Richmond, VA 23298-0678, USA
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11
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Suzuki YA, Wong H, Ashida KY, Schryvers AB, Lönnerdal B. The N1 domain of human lactoferrin is required for internalization by caco-2 cells and targeting to the nucleus. Biochemistry 2008; 47:10915-20. [PMID: 18785755 DOI: 10.1021/bi8012164] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human lactoferrin (hLf) has been shown to interact with cells from the Caco-2 human small intestinal cell line. There currently is little information about the molecular details of its interaction. As a first step toward detailed characterization of this interaction, we used a series of Lf chimeras to analyze which part of Lf is responsible for the interaction with Caco-2 cells. Recombinant chimeric proteins consisting of segments of hLf and bovine transferrin (bTf) were produced in a baculovirus-insect cell system and purified by a combination of cation exchange chromatography and immobilized bTf antibody affinity chromatography. Each chimera was labeled with a green fluorescent dye to monitor its interaction with Caco-2 cells. Similarly, the intestinal Lf receptor (LfR), also known as intelectin, was probed with an anti-LfR antibody that was detected with a secondary antibody conjugated with a red-color fluorescent dye. The results demonstrated that chimeric proteins containing the N-lobe or the N1.1 subdomain of Lf bound as well as intact Lf to Caco-2 cells. Confocal microscopy analysis revealed that these proteins, along with the LfR, were internalized and targeted to the nucleus. These results indicate that the N1.1 subdomain of hLf is sufficient for binding, internalization, and targeting to the nucleus of Caco-2 cells.
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Affiliation(s)
- Yasushi A Suzuki
- Department of Nutrition, University of California, Davis, California 95616, USA
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12
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Perera Y, García D, Guirola O, Huerta V, García Y, Muñoz Y. Epitope mapping of anti-human transferrin monoclonal antibodies: potential uses for transferrin–transferrin receptor interaction studies. J Mol Recognit 2008; 21:103-13. [DOI: 10.1002/jmr.878] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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13
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Price GA, Masri HP, Hollander AM, Russell MW, Cornelissen CN. Gonococcal transferrin binding protein chimeras induce bactericidal and growth inhibitory antibodies in mice. Vaccine 2007; 25:7247-60. [PMID: 17720283 PMCID: PMC2225598 DOI: 10.1016/j.vaccine.2007.07.038] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Revised: 05/11/2007] [Accepted: 07/12/2007] [Indexed: 12/22/2022]
Abstract
We have previously demonstrated the full-length gonococcal transferrin binding proteins (TbpA and TbpB) to be promising antigens in the development of a protective vaccine against Neisseria gonorrhoeae. In the current study we employed a genetic chimera approach fusing domains from TbpA and TbpB to the A2 domain of cholera toxin, which naturally binds in a non-covalent fashion to the B subunit of cholera toxin during assembly. For one construct, the N-terminal half of TbpB (NB) was fused to the A2 subunit of cholera toxin. In a second construct, the loop 2 region (L2) of TbpA was genetically fused between the NB domain and the A2 domain, generating a double chimera. Both chimeras were immunogenic and induced serum bactericidal and vaginal growth-inhibiting antibodies. This study highlights the potential of using protective epitopes instead of full-length proteins in the development of an efficacious gonococcal vaccine.
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Affiliation(s)
- Gregory A. Price
- Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298 USA
| | - Heather P. Masri
- Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298 USA
| | - Aimee M. Hollander
- Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298 USA
| | - Michael W. Russell
- Departments of Oral Biology and Microbiology and Immunology, Witebsky Center for Microbial Pathogenesis and Immunology, University at Buffalo, Buffalo, New York
| | - Cynthia Nau Cornelissen
- Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298 USA
- To whom correspondence should be addressed Mailing address: P.O. Box 980678, Richmond, VA 23298-0678, , Phone: (804) 827-1754, Fax: (804) 828-9946
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Khan A, Shouldice S, Kirby S, Yu RH, Tari L, Schryvers A. High-affinity binding by the periplasmic iron-binding protein from Haemophilus influenzae is required for acquiring iron from transferrin. Biochem J 2007; 404:217-25. [PMID: 17313366 PMCID: PMC1868806 DOI: 10.1042/bj20070110] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The periplasmic iron-binding protein, FbpA (ferric-ion-binding protein A), performs an essential role in iron acquisition from transferrin in Haemophilus influenzae. A series of site-directed mutants in the metal-binding amino acids of FbpA were prepared to determine their relative contribution to iron binding and transport. Structural studies demonstrated that the mutant proteins crystallized in an open conformation with the iron atom associated with the C-terminal domain. The iron-binding properties of the mutant proteins were assessed by several assays, including a novel competitive iron-binding assay. The relative ability of the proteins to compete for iron was pH dependent, with a rank order at pH 6.5 of wild-type, Q58L, H9Q>H9A, E57A>Y195A, Y196A. The genes encoding the mutant FbpA were introduced into H. influenzae and the resulting strains varied in the level of ferric citrate required to support growth on iron-limited medium, suggesting a rank order for metal-binding affinities under physiological conditions comparable with the competitive binding assay at pH 6.5 (wild-type=Q58L>H9Q>H9A, E57A>Y195A, Y196A). Growth dependence on human transferrin was only obtained with cells expressing wild-type, Q58L or H9Q FbpAs, proteins with stability constants derived from the competition assay >2.0x10(18) M(-1). These results suggest that a relatively high affinity of iron binding by FbpA is required for removal of iron from transferrin and its transport across the outer membrane.
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Affiliation(s)
- Ali G. Khan
- *Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, AB, Canada T2N 4N1
| | - Stephen R. Shouldice
- *Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, AB, Canada T2N 4N1
| | - Shane D. Kirby
- *Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, AB, Canada T2N 4N1
| | - Rong-hua Yu
- *Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, AB, Canada T2N 4N1
| | | | - Anthony B. Schryvers
- *Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, AB, Canada T2N 4N1
- To whom correspondence should be addressed (email )
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DeRocco AJ, Cornelissen CN. Identification of transferrin-binding domains in TbpB expressed by Neisseria gonorrhoeae. Infect Immun 2007; 75:3220-32. [PMID: 17438025 PMCID: PMC1932913 DOI: 10.1128/iai.00072-07] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The transferrin iron acquisition system of Neisseria gonorrhoeae is necessary for iron uptake from transferrin in the human host and requires the participation of two distinct proteins: TbpA and TbpB. TbpA is a TonB-dependent outer membrane transporter responsible for the transport of iron into the cell. TbpB is a lipid-modified protein, for which a precise role in receptor function has not yet been elucidated. These receptor complex proteins show promise as vaccine candidates; therefore, it is important to identify surface-exposed regions of the proteins required for wild-type functions. In this study we examined TbpB, which has been reported to be surface exposed in its entirety; however, this hypothesis has never been tested experimentally. We placed the hemagglutinin (HA) epitope into TbpB with the dual purpose of examining the surface exposure of particular epitopes as well as their impact on receptor function. Nine insertion mutants were created, placing the epitope downstream of the signal peptidase II cleavage site. We report that the HA epitope is surface accessible in all mutants, indicating that the full-length TbpB is completely surface exposed. By expressing the TbpB-HA fusion proteins in N. gonorrhoeae, we were able to examine the impact of each insertion on the function of TbpB and the transferrin acquisition process. We propose that TbpB is comprised of two transferrin-binding-competent lobes, both of which are critical for efficient iron uptake from human transferrin.
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Affiliation(s)
- Amanda J DeRocco
- Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, VA 23298-0678, USA
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Izadi-Pruneyre N, Huché F, Lukat-Rodgers GS, Lecroisey A, Gilli R, Rodgers KR, Wandersman C, Delepelaire P. The heme transfer from the soluble HasA hemophore to its membrane-bound receptor HasR is driven by protein-protein interaction from a high to a lower affinity binding site. J Biol Chem 2006; 281:25541-50. [PMID: 16774915 DOI: 10.1074/jbc.m603698200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
HasA is an extracellular heme binding protein, and HasR is an outer membrane receptor protein from Serratia marcescens. They are the initial partners of a heme internalization system allowing S. marcescens to scavenge heme at very low concentrations due to the very high affinity of HasA for heme (Ka = 5,3 x 10(10) m(-1)). Heme is then transferred to HasR, which has a lower affinity for heme. The mechanism of the heme transfer between HasA and HasR is largely unknown. HasR has been overexpressed and purified in holo and apo forms. It binds one heme molecule with a Ka of 5 x 10(6) m(-1) and shows the characteristic absorbance spectrum of a low spin heme iron. Both holoHasA and apoHasA bind tightly to apoHasR in a 1:1 stoichiometry. In this study we show that heme transfer occurs in vitro in the purified HasA.HasR complex, demonstrating that heme transfer is energy- and TonB complex-independent and driven by a protein-protein interaction. We also show that heme binding to HasR involves two conserved histidine residues.
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Affiliation(s)
- Nadia Izadi-Pruneyre
- Unité des Membranes Bactériennes, CNRS URA 2172 Département de Microbiologie, Institut Pasteur, 75724 Paris Cedex 15 France
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Ling JML, Schryvers AB. Perspectives on interactions between lactoferrin and bacteriaThis paper is one of a selection of papers published in this Special Issue, entitled 7th International Conference on Lactoferrin: Structure, Function, and Applications, and has undergone the Journal's usual peer review process. Biochem Cell Biol 2006; 84:275-81. [PMID: 16936797 DOI: 10.1139/o06-044] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Lactoferrin has long been recognized for its antimicrobial properties, initially attributed primarily to iron sequestration. It has since become apparent that interaction between the host and bacteria is modulated by a complex series of interactions between lactoferrin and bacteria, lactoferrin and bacterial products, and lactoferrin and host cells. The primary focus of this review is the interaction between lactoferrin and bacteria, but interactions with the lactoferrin-derived cationic peptide lactoferricin will also be discussed. We will summarize what is currently known about the interaction between lactoferrin (or lactoferricin) and surface or secreted bacterial components, comment on the potential physiological relevance of the findings, and identify key questions that remain unanswered.
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Affiliation(s)
- Jessmi M L Ling
- Department of Microbiology and Infectious Diseases, 274 Heritage Medical Research Building, Faculty of Medicine, University of Calgary, 3330 Hospital Dr. N.W, Calgary, AB T2N 4N1, Canada
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Cantini F, Savino S, Scarselli M, Masignani V, Pizza M, Romagnoli G, Swennen E, Veggi D, Banci L, Rappuoli R. Solution structure of the immunodominant domain of protective antigen GNA1870 of Neisseria meningitidis. J Biol Chem 2005; 281:7220-7. [PMID: 16407174 DOI: 10.1074/jbc.m508595200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GNA1870, a 28-kDa surface-exposed lipoprotein of Neisseria meningitidis recently discovered by reverse vaccinology, is one of the most potent antigens of Meningococcus and a promising candidate for a universal vaccine against a devastating disease. Previous studies of epitope mapping and genetic characterization identified residues critical for bactericidal response within the C-terminal domain of the molecule. To elucidate the conformation of protective epitopes, we used NMR spectroscopy to obtain the solution structure of the immunodominant 18-kDa C-terminal portion of GNA1870. The structure consists of an eight-stranded antiparallel beta-barrel overlaid by a short alpha-helix with an unstructured N-terminal end. Residues previously shown to be important for antibody recognition were mapped on loops facing the same ridge of the molecule. The sequence similarity of GNA1870 with members of the bacterial transferrin receptor family allows one to predict the folding of this class of well known bacterial antigens, providing the basis for the rational engineering of high affinity B cell epitopes.
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Affiliation(s)
- Francesca Cantini
- Centro Risonanze Magnetiche (CERM), University of Florence, Via L. Sacconi 6, 50019 Sesto Fiorentino, Italy
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Agarwal S, King CA, Klein EK, Soper DE, Rice PA, Wetzler LM, Genco CA. The gonococcal Fur-regulated tbpA and tbpB genes are expressed during natural mucosal gonococcal infection. Infect Immun 2005; 73:4281-7. [PMID: 15972520 PMCID: PMC1168583 DOI: 10.1128/iai.73.7.4281-4287.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2004] [Revised: 01/04/2005] [Accepted: 03/02/2005] [Indexed: 11/20/2022] Open
Abstract
Iron is limiting in the human host, and bacterial pathogens respond to this environment by regulating gene expression through the ferric uptake regulator protein (Fur). In vitro studies have demonstrated that Neisseria gonorrhoeae controls the expression of several critical genes through an iron- and Fur-mediated mechanism. While most in vitro experiments are designed to determine the response of N. gonorrhoeae to an exogenous iron concentration of zero, these organisms are unlikely to be exposed to such severe limitations of iron in vivo. To determine if N. gonorrhoeae expresses iron- and Fur-regulated genes in vivo during uncomplicated gonococcal infection, we examined gene expression profiles of specimens obtained from male subjects with urethral infections. RNA was isolated from urethral swab specimens and used as a template to amplify, by reverse transcriptase PCR (RT-PCR), gonococcal genes known to be regulated by iron and Fur (tbpA, tbpB, and fur). The constitutively expressed gonococcal rmp gene was used as a positive control. RT-PCR analysis indicated that gonorrhea-positive specimens where rmp expression was seen were also 93% (51/55) fbpA positive, 87% (48/55) tbpA positive, and 86% (14 of 16 tested) tbpB positive. In addition, we detected a fur transcript in 79% (37 of 47 tested) of positive specimens. We also measured increases in levels of immunoglobulin G antibody against TbpA (91%) and TbpB (73%) antigens in sera from infected male subjects compared to those in uninfected controls. A positive trend between tbpA gene expression and TbpA antibody levels in sera indicated a relationship between levels of gene expression and immune response in male subjects infected with gonorrhea for the first time. These results indicate that gonococcal iron- and Fur-regulated tbpA and tbpB genes are expressed in gonococcal infection and that male subjects with mucosal gonococcal infections exhibit antibodies to these proteins.
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Affiliation(s)
- Sarika Agarwal
- Department of Medicine, Section of Infectious Diseases, Boston University School of Medicine, 650 Albany Street, Room 637, Boston, Massachusetts 02118, USA
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Stokes RH, Oakhill JS, Joannou CL, Gorringe AR, Evans RW. Meningococcal transferrin-binding proteins A and B show cooperation in their binding kinetics for human transferrin. Infect Immun 2005; 73:944-52. [PMID: 15664936 PMCID: PMC546982 DOI: 10.1128/iai.73.2.944-952.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Neisseria meningitidis, a causative agent of bacterial meningitis and septicemia, obtains transferrin-bound iron by expressing two outer membrane-located transferrin-binding proteins, TbpA and TbpB. A novel system was developed to investigate the interaction between Tbps and human transferrin. Copurified TbpA-TbpB, recombined TbpA-TbpB, and individual TbpA and TbpB were reconstituted into liposomes and fused onto an HPA chip (BIAcore). All preparations formed stable monolayers, which, with the exception of TbpB, could be regenerated by removing bound transferrin. The ligand binding properties of these monolayers were characterized with surface plasmon resonance and shown to be specific for human transferrin. Kinetic data for diferric human transferrin binding showed that recombined TbpA-TbpB had K(a) and K(d) values similar to those of copurified TbpA-TbpB. Individual TbpA and TbpB also displayed K(a) values similar to those of copurified TbpA-TbpB, but their K(d) values were one order of magnitude higher. Chemical cross-linking studies revealed that TbpA and TbpB, in the absence of human transferrin, formed large complexes with TbpA as the predominant species. Upon human transferrin binding, a complex was formed with a molecular mass corresponding to that of a TbpB-human transferrin heterodimer as well as a higher-molecular-mass complex of this heterodimer cross-linked to TbpA. This indicates that TbpA and TbpB form a functional meningococcal receptor complex in which there is cooperativity in the human transferrin binding kinetics. However, iron loss from the diferric human transferrin-TbpA-TbpB complex was not greater than that from human transferrin alone, suggesting that additional meningococcal transport components are involved in the process of iron removal.
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Affiliation(s)
- Russell H Stokes
- Metalloprotein Research Group, Randall Division of Cell and Molecular Biophysics, GKT School of Biomedical Sciences, King's College London, Guy's Campus, New Hunt's House, London SE1 1UL, United Kingdom
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Abstract
Iron is an essential element for most organisms, including bacteria. The oxidized form is insoluble, and the reduced form is highly toxic for most macromolecules and, in biological systems, is generally sequestrated by iron- and heme-carrier proteins. Thus, despite its abundance on earth, there is practically no free iron available for bacteria whatever biotope they colonize. To fulfill their iron needs, bacteria have multiple iron acquisition systems, reflecting the diversity of their potential biotopes. The iron/heme acquisition systems in bacteria have one of two general mechanisms. The first involves direct contact between the bacterium and the exogenous iron/heme sources. The second mechanism relies on molecules (siderophores and hemophores) synthesized and released by bacteria into the extracellular medium; these molecules scavenge iron or heme from various sources. Recent genetic, biochemical, and crystallographic studies have allowed substantial progress in describing molecular mechanisms of siderophore and hemophore interactions with the outer membrane receptors, transport through the inner membrane, iron storage, and regulation of genes encoding biosynthesis and uptake proteins.
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Affiliation(s)
- Cécile Wandersman
- Unité des Membranes Bactériennes, Département de Microbiologie Fondamentale et Médicale, Institut Pasteur, 75724 Paris Cedex 15, France.
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Nemish U, Yu RH, Tari LW, Krewulak K, Schryvers AB. The bacterial receptor protein, transferrin-binding protein B, does not independently facilitate the release of metal ion from human transferrin. Biochem Cell Biol 2004; 81:275-83. [PMID: 14569300 DOI: 10.1139/o03-057] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pathogenic Gram-negative bacteria of the Pasteurellaceae and Neisseriaceae acquire iron for growth from host transferrin through the action of specific surface receptors. Iron is removed from transferrin by the receptor at the cell surface and is transported across the outer membrane to the periplasm. A periplasmic binding protein-dependent pathway subsequently transports iron into the cell. The transferrin receptor is composed of a largely surface-exposed lipoprotein, transferrin binding protein B, and a TonB-dependent integral outer membrane protein, transferrin binding protein A. To examine the role of transferrin binding protein B in the iron removal process, complexes of recombinant transferrin binding protein B and transferrin were prepared and compared with transferrin in metal-binding and -removal experiments. A polyhistidine-tagged form of recombinant transferrin binding protein B was able to purify a complex with transferrin that was largely monodisperse by dynamic light scattering analysis. Gallium was used instead of iron in the metal-binding studies, since it resulted in increased stability of recombinant transferrin binding protein B in the complex. Difference absorption spectra were used to monitor removal of gallium by nitrilotriacetic acid. Kinetic and equilibrium binding studies indicated that transferrin binds gallium more tightly in the presence of transferrin binding protein B. Thus, transferrin binding protein B does not facilitate metal ion removal and additional components are required for this process.
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Affiliation(s)
- Ulyana Nemish
- Department of Biological Sciences, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
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Perkins-Balding D, Ratliff-Griffin M, Stojiljkovic I. Iron transport systems in Neisseria meningitidis. Microbiol Mol Biol Rev 2004; 68:154-71. [PMID: 15007100 PMCID: PMC362107 DOI: 10.1128/mmbr.68.1.154-171.2004] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Acquisition of iron and iron complexes has long been recognized as a major determinant in the pathogenesis of Neisseria meningitidis. In this review, high-affinity iron uptake systems, which allow meningococci to utilize the human host proteins transferrin, lactoferrin, hemoglobin, and haptoglobin-hemoglobin as sources of essential iron, are described. Classic features of bacterial iron transport systems, such as regulation by the iron-responsive repressor Fur and TonB-dependent transport activity, are discussed, as well as more specific features of meningococcal iron transport. Our current understanding of how N. meningitidis acquires iron from the human host and the vaccine potentials of various components of these iron transport systems are also reviewed.
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Affiliation(s)
- Donna Perkins-Balding
- Rollins Research Center, Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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Renauld-Mongénie G, Lins L, Krell T, Laffly L, Mignon M, Dupuy M, Delrue RM, Guinet-Morlot F, Brasseur R, Lissolo L. Transferrin-binding protein B of Neisseria meningitidis: sequence-based identification of the transferrin-Binding site confirmed by site-directed mutagenesis. J Bacteriol 2004; 186:850-7. [PMID: 14729713 PMCID: PMC321495 DOI: 10.1128/jb.186.3.850-857.2004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2003] [Accepted: 10/24/2003] [Indexed: 11/20/2022] Open
Abstract
A sequence-based prediction method was employed to identify three ligand-binding domains in transferrin-binding protein B (TbpB) of Neisseria meningitidis strain B16B6. Site-directed mutagenesis of residues located in these domains has led to the identification of two domains, amino acids 53 to 57 and 240 to 245, which are involved in binding to human transferrin (htf). These two domains are conserved in an alignment of different TbpB sequences from N. meningitidis and Neisseria gonorrhoeae, indicating a general functional role of the domains. Western blot analysis and BIAcore and isothermal titration calorimetry experiments demonstrated that site-directed mutations in both binding domains led to a decrease or abolition of htf binding. Analysis of mutated proteins by circular dichroism did not provide any evidence for structural alterations due to the amino acid replacements. The TbpB mutant R243N was devoid of any htf-binding activity, and antibodies elicited by the mutant showed strong bactericidal activity against the homologous strain, as well as against several heterologous tbpB isotype I strains.
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Létoffé S, Debarbieux L, Izadi N, Delepelaire P, Wandersman C. Ligand delivery by haem carrier proteins: the binding of Serratia marcescens haemophore to its outer membrane receptor is mediated by two distinct peptide regions. Mol Microbiol 2003; 50:77-88. [PMID: 14507365 DOI: 10.1046/j.1365-2958.2003.03686.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Haem is involved in essential processes. It is toxic and thus is not found free in living organisms but almost entirely sequestered by haem carrier proteins. We investigated the mechanisms of haem transfer between the proteins of a bacterial haem acquisition system involving haemophores. Haemophores are secreted by several Gram-negative bacteria and are able to extract haem (assimilated as an iron source) from haemoproteins and deliver it to specific outer membrane receptors. The Serratia marcescens haemophore (HasA) is folded into a globular form and tyrosine and histidine are involved in haem ligation. Interaction with the receptor is of high affinity (5 nM) and does not involve haem. Identification and study of mutants with altered binding properties led to the description of two regions of the haemophore that bind to the receptor. They consist of residues involved in two beta strands located on the same side of HasA. Each region is sufficient for high affinity binding. The synthetic peptide corresponding to one beta strand competes with the corresponding haemophore region for binding to the receptor, suggesting that the two binding regions are independent binding sites. We propose a model for haem release and transfer to the receptor.
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Affiliation(s)
- Sylvie Létoffé
- Unité des Membranes Bactériennes, Institut Pasteur (CNRS URA2172) 25 rue du Dr Roux, 75724 Paris Cedex 15, France
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26
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Krell T, Renauld-Mongénie G, Nicolaï MC, Fraysse S, Chevalier M, Bérard Y, Oakhill J, Evans RW, Gorringe A, Lissolo L. Insight into the structure and function of the transferrin receptor from Neisseria meningitidis using microcalorimetric techniques. J Biol Chem 2003; 278:14712-22. [PMID: 12571247 DOI: 10.1074/jbc.m204461200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transferrin receptor of Neisseria meningitidis is composed of the transmembrane protein TbpA and the outer membrane protein TbpB. Both receptor proteins have the capacity to independently bind their ligand human transferrin (htf). To elucidate the specific role of these proteins in receptor function, isothermal titration calorimetry was used to study the interaction between purified TbpA, TbpB or the entire receptor (TbpA + TbpB) with holo- and apo-htf. The entire receptor was shown to contain a single high affinity htf-binding site on TbpA and approximately two lower affinity binding sites on TbpB. The binding sites appear to be independent. Purified TbpA was shown to have strong ligand preference for apo-htf, whereas TbpA in the receptor complex with TbpB preferentially binds the holo form of htf. The orientation of the ligand specificity of TbpA toward holo-htf is proposed to be the physiological function of TbpB. Furthermore, the thermodynamic mode of htf binding by TbpB of isotypes I and II was shown to be different. A protocol for the generation of active, histidine-tagged TbpB as well as its individual N- and C-terminal domains is presented. Both domains are shown to strongly interact with each other, and isothermal titration calorimetry and circular dichroism experiments provide clear evidence for this interaction causing conformational changes. The N-terminal domain of TbpB was shown to be the site of htf binding, whereas the C-terminal domain is not involved in binding. Furthermore, the interactions between TbpA and the different domains of TbpB have been demonstrated.
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Affiliation(s)
- Tino Krell
- Aventis Pasteur, 1541 avenue Marcel Mérieux, 69280 Marcy l'Etoile, France.
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27
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Sims KL, Schryvers AB. Peptide-peptide interactions between human transferrin and transferrin-binding protein B from Moraxella catarrhalis. J Bacteriol 2003; 185:2603-10. [PMID: 12670985 PMCID: PMC152632 DOI: 10.1128/jb.185.8.2603-2610.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Transferrin-binding protein B (TbpB) is one component of a bipartite receptor in several gram-negative bacterial species that binds host transferrin and mediates the uptake of iron for growth. Transferrin and TbpB are both bilobed proteins, and the interaction between these proteins seems to involve similar lobe-lobe interactions. Synthetic overlapping peptide libraries representing the N lobe of TbpB from Moraxella catarrhalis were prepared and probed with labeled human transferrin. Transferrin-binding peptides were localized to six different regions of the TbpB N lobe, and reciprocal experiments identified six different regions of the C lobe of transferrin that bound TbpB. Truncations of the N lobe of TbpB that sequentially removed each transferrin-binding determinant were used to probe an overlapping peptide library of the C lobe of human transferrin. The removal of each TbpB N-lobe transferrin-binding determinant resulted in a loss of reactivity with peptides from the synthetic peptide library representing the C lobe of transferrin. Thus, individual peptide-peptide interactions between ligand and receptor were identified. A structural model of human transferrin was used to map surface regions capable of binding to TbpB.
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Affiliation(s)
- Kurtis L Sims
- Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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28
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Bergman NH, Akerley BJ. Position-based scanning for comparative genomics and identification of genetic islands in Haemophilus influenzae type b. Infect Immun 2003; 71:1098-108. [PMID: 12595420 PMCID: PMC148883 DOI: 10.1128/iai.71.3.1098-1108.2003] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacteria exhibit extensive genetic heterogeneity within species. In many cases, these differences account for virulence properties unique to specific strains. Several such loci have been discovered in the genome of the type b serotype of Haemophilus influenzae, a human pathogen able to cause meningitis, pneumonia, and septicemia. Here we report application of a PCR-based scanning procedure to compare the genome of a virulent type b (Hib) strain with that of the laboratory-passaged Rd KW20 strain for which a complete genome sequence is available. We have identified seven DNA segments or H. influenzae genetic islands (HiGIs) present in the type b genome and absent from the Rd genome. These segments vary in size and content and show signs of horizontal gene transfer in that their percent G+C content differs from that of the rest of the H. influenzae genome, they contain genes similar to those found on phages or other mobile elements, or they are flanked by DNA repeats. Several of these loci represent potential pathogenicity islands, because they contain genes likely to mediate interactions with the host. These newly identified genetic islands provide areas of investigation into both the evolution and pathogenesis of H. influenzae. In addition, the genome scanning approach developed to identify these islands provides a rapid means to compare the genomes of phenotypically diverse bacterial strains once the genome sequence of one representative strain has been determined.
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Affiliation(s)
- Nicholas H Bergman
- Department of Microbiology & Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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29
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Yu RH, Schryvers AB. Bacterial lactoferrin receptors: insights from characterizing the Moraxella bovis receptors. Biochem Cell Biol 2002; 80:81-90. [PMID: 11908647 DOI: 10.1139/o01-235] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Moraxella bovis is the causative agent of infectious conjunctivitis in cattle. Moraxella bovis isolates were shown to specifically bind bovine lactoferrin (bLf) and bovine transferrin (bTf) and to use these proteins as a source of iron to support the growth of iron-limited cells. Affinity isolation experiments with immobilized bTf yielded two proteins readily resolved by SDS-PAGE analysis, whereas only a single band of approximately 100 kDa was detected when immobilized bLf was used as the affinity ligand. Using a novel cloning strategy, regions containing the genes encoding the lactoferrin (Lf) and transferrin (Tf) receptor proteins were isolated and sequenced, demonstrating that they both consisted of two genes, with the tbpB or lbpB gene preceding the tbpA or lbpA gene. The cloned lbp genes were used to generate isogenic mutants deficient in lactoferrin binding protein A and (or) B, and the resulting strains were tested in growth and binding assays. The isogenic mutants were deficient in their use of bLf for growth and had substantially diminished bLf binding capability. The predicted amino acid sequence from the segment encoding Lf binding protein B revealed an internal amino acid homology suggesting it is a bi-lobed protein, with a C-lobe enriched in acidic amino acids, but without the evident clustering observed in Lf-binding proteins from other species.
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Affiliation(s)
- Rong-Hua Yu
- Department of Microbiology and Infectious Diseases, University of Calgary, Alberta, Canada
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30
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Sethi S, Murphy TF. Bacterial infection in chronic obstructive pulmonary disease in 2000: a state-of-the-art review. Clin Microbiol Rev 2001; 14:336-63. [PMID: 11292642 PMCID: PMC88978 DOI: 10.1128/cmr.14.2.336-363.2001] [Citation(s) in RCA: 408] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States. The precise role of bacterial infection in the course and pathogenesis of COPD has been a source of controversy for decades. Chronic bacterial colonization of the lower airways contributes to airway inflammation; more research is needed to test the hypothesis that this bacterial colonization accelerates the progressive decline in lung function seen in COPD (the vicious circle hypothesis). The course of COPD is characterized by intermittent exacerbations of the disease. Studies of samples obtained by bronchoscopy with the protected specimen brush, analysis of the human immune response with appropriate immunoassays, and antibiotic trials reveal that approximately half of exacerbations are caused by bacteria. Nontypeable Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae are the most common causes of exacerbations, while Chlamydia pneumoniae causes a small proportion. The role of Haemophilus parainfluenzae and gram-negative bacilli remains to be established. Recent progress in studies of the molecular mechanisms of pathogenesis of infection in the human respiratory tract and in vaccine development guided by such studies promises to lead to novel ways to treat and prevent bacterial infections in COPD.
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Affiliation(s)
- S Sethi
- Division of Pulmonary and Critical Medicine, State University of New York at Buffalo, Buffalo, New York, USA
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31
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Abstract
Transferrins are iron-binding proteins that are involved in iron storage and resistance to bacterial disease. Previous work has shown that nonsynonymous-to-synonymous-site substitution ratios (d(n)/d(s) ratios) between transferrin genes from some salmonid species were significantly greater than 1.0, providing evidence for positive selection at the transferrin gene. The purpose of the current study was to put these earlier results in a broader evolutionary context by examining variation among 25 previously published transferrin sequences from fish, amphibians, and mammals. The results of the study show that evidence for positive selection at transferrin is limited to salmonids-d(n)/d(s) ratios estimated for nonsalmonid lineages were generally less than 1.0. Within the salmonids, approximately 13% of the transferrin codon sites are estimated to be subject to positive selection, with an estimated d(n)/d(s) ratio of approximately 7. The three- dimensional locations of some of the selected sites were inferred by comparing these sites to homologous sites in the bovine lactoferrin crystallographic structure. The selected sites generally fall on the outside of the molecule, within and near areas that are bound by transferrin-binding proteins from human pathogenic bacteria. The physical locations of sites estimated to be subject to positive selection support previous speculation that competition for iron from pathogenic bacteria could be the source of positive selection.
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Affiliation(s)
- M J Ford
- National Marine Fisheries Service, Northwest Fisheries Science Center, Conservation Biology Division, Seattle, Washington 98112, USA.
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Kahler CM, Blum E, Miller YK, Ryan D, Popovic T, Stephens DS. exl, an exchangeable genetic island in Neisseria meningitidis. Infect Immun 2001; 69:1687-96. [PMID: 11179344 PMCID: PMC98073 DOI: 10.1128/iai.69.3.1687-1696.2001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genetic structure and evolution of a novel exchangeable meningococcal genomic island was defined for the important human pathogen Neisseria meningitidis. In 125 meningococcal strains tested, one of three unrelated nucleotide sequences, designated exl (exchangeable locus), was found between a gene required for heme utilization, hemO, and col, encoding a putative Escherichia coli collagenase homologue. The 5' boundary of each exl cassette was the stop codon of hemO, whereas the 3' boundary was delineated by a 33-bp repeat containing neisserial uptake sequences located downstream of col. One of the three alternative exl cassettes contained the meningococcal hemoglobin receptor gene, hmbR (exl3). In other meningococcal strains, hmbR was absent from the genome and was replaced by either a nucleotide sequence containing a novel open reading frame, exl2, or a cassette containing exl3. The proteins encoded by exl2 and exl3 had no significant amino acid homology to HmbR but contained six motifs that are also present in the lipoprotein components of the lactoferrin (LbpB), transferrin (TbpB), and hemoglobin-haptoglobin (HpuA) uptake systems. To determine the evolutionary relationships among meningococci carrying hmbR, exl2, or exl3, isolates representing 92 electrophoretic types were examined. hmbR was found throughout the population structure of N. meningitidis (genetic distance, >0.425), whereas exl2 and exl3 were found in clonal groups at genetic distances of <0.2. The commensal neisserial species were identified as reservoirs for all of the exl cassettes found in meningococci. The structure of these cassettes and their correlation with clonal groups emphasize the extensive gene pool and frequent horizontal DNA transfer events that contribute to the evolution and virulence of N. meningitidis.
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Affiliation(s)
- C M Kahler
- Department of Medicine and Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA.
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33
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Ogunnariwo JA, Schryvers AB. Characterization of a novel transferrin receptor in bovine strains of Pasteurella multocida. J Bacteriol 2001; 183:890-6. [PMID: 11208786 PMCID: PMC94955 DOI: 10.1128/jb.183.3.890-896.2001] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Analysis of bovine respiratory isolates of Pasteurella multocida demonstrated that six of nine strains tested were capable of growth dependent upon bovine transferrin and of specifically binding ruminant transferrins. A single 82-kDa protein was affinity isolated from the P. multocida strains with immobilized bovine transferrin. In contrast to what has been observed in other species, binding of this protein to immobilized transferrin was specifically blocked by the N-lobe subfragment of bovine transferrin. A single gene encoding the 82-kDa protein was flanked by a leucyl-tRNA synthetase gene and an IS1060 element, in contrast to other species where genes encoding the two receptor proteins (TbpB and TbpA) are found in an operonic arrangement. A similar gene arrangement was observed in all of the receptor-positive strains, in spite of the observation that they belonged to different genomic groups. Analysis of the deduced amino acid sequence of the receptor protein indicated that it is a member of the TonB-dependent outer membrane receptor family, and although it is related to transferrin and lactoferrin receptor proteins (TbpAs and LbpAs) from other species, it differs substantially from other members of this group. Amino acid alignments suggest that the reduced size (20 kDa smaller) of the P. multocida TbpA is primarily due to the absence of larger predicted external loops. Collectively these results suggest that P. multocida has a single, novel receptor protein (TbpA) that is capable of efficiently mediating iron acquisition from bovine transferrin without the involvement of a second receptor protein (TbpB).
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Affiliation(s)
- J A Ogunnariwo
- Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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Rokbi B, Renauld-Mongenie G, Mignon M, Danve B, Poncet D, Chabanel C, Caugant DA, Quentin-Millet MJ. Allelic diversity of the two transferrin binding protein B gene isotypes among a collection of Neisseria meningitidis strains representative of serogroup B disease: implication for the composition of a recombinant TbpB-based vaccine. Infect Immun 2000; 68:4938-47. [PMID: 10948108 PMCID: PMC101705 DOI: 10.1128/iai.68.9.4938-4947.2000] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The distribution of the two isotypes of tbpB in a collection of 108 serogroup B meningococcal strains belonging to the four major clonal groups associated with epidemic and hyperendemic disease (the ET-37 complex, the ET-5 complex, lineage III, and cluster A4) was determined. Isotype I strains (with a 1.8-kb tbpB gene) was less represented than isotype II strains (19.4 versus 80.6%). Isotype I was restricted to the ET-37 complex strains, while isotype II was found in all four clonal complexes. The extent of the allelic diversity of tbpB in these two groups was studied by PCR restriction analysis and sequencing of 10 new tbpB genes. Four major tbpB gene variants were characterized: B16B6 (representative of isotype I) and M982, BZ83, and 8680 (representative of isotype II). The relevance of these variants was assessed at the antigenic level by the determination of cross-bactericidal activity of purified immunoglobulin G preparations raised to the corresponding recombinant TbpB (rTbpB) protein against a panel of 27 strains (5 of isotype I and 22 of isotype II). The results indicated that rTbpB corresponding to each variant was able to induce cross-bactericidal antibodies. However, the number of strains killed with an anti-rTbpB serum was slightly lower than that obtained with an anti-TbpA(+)B complex. None of the sera tested raised against an isotype I strain was able to kill an isotype II strain and vice versa. None of the specific antisera tested (anti-rTbpB or anti-TbpA(+)B complex) was able to kill all of the 22 isotype II strains tested. Moreover, using sera raised against the C-terminus domain of TbpB M982 (amino acids 352 to 691) or BZ83 (amino acids 329 to 669) fused to the maltose-binding protein, cross-bactericidal activity was detected against 12 and 7 isotype II strains, respectively, of the 22 tested. These results suggest surface accessibility of the C-terminal end of TbpB. Altogether, these results show that although more than one rTbpB will be required in the composition of a TbpB-based vaccine to achieve a fully cross-bactericidal activity, rTbpB and its C terminus were able by themselves to induce cross-bactericidal antibodies.
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Affiliation(s)
- B Rokbi
- Aventis Pasteur, Marcy-L'Etoile, France.
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Abstract
Pathogenic neisseriae have a repertoire of high-affinity iron uptake systems to facilitate acquisition of this essential element in the human host. They possess surface receptor proteins that directly bind the extracellular host iron-binding proteins transferrin and lactoferrin. Alternatively, they have siderophore receptors capable of scavenging iron when exogenous siderophores are present. Released intracellular haem iron present in the form of haemoglobin, haemoglobin-haptoglobin or free haem can be used directly as a source of iron for growth through direct binding by specific surface receptors. Although these receptors may vary in complexity and composition, the key protein involved in the transport of iron (as iron, haem or iron-siderophore) across the outer membrane is a TonB-dependent receptor with an overall structure presumably similar to that determined recently for Escherichia coli FhuA or FepA. The receptors are potentially ideal vaccine targets in view of their critical role in survival in the host. Preliminary pilot studies indicate that transferrin receptor-based vaccines may be protective in humans.
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Affiliation(s)
- A B Schryvers
- Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.
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