1
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Schalk IJ. Bacterial siderophores: diversity, uptake pathways and applications. Nat Rev Microbiol 2024:10.1038/s41579-024-01090-6. [PMID: 39251840 DOI: 10.1038/s41579-024-01090-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/19/2024] [Indexed: 09/11/2024]
Abstract
Iron is an essential nutrient for the growth, survival and virulence of almost all bacteria. To access iron, many bacteria produce siderophores, molecules with a high affinity for iron. Research has highlighted substantial diversity in the chemical structure of siderophores produced by bacteria, as well as remarkable variety in the molecular mechanisms involved in strategies for acquiring iron through these molecules. The metal-chelating properties of siderophores, characterized by their high affinity for iron and ability to chelate numerous other metals (albeit with lower affinity compared with iron), have also generated interest in diverse fields. Siderophores find applications in the environment, such as in bioremediation and agriculture, in which emerging and innovative strategies are being developed to address pollution and enhance nutrient availability for plants. Moreover, in medicine, siderophores could be used as a tool for novel antimicrobial therapies and medical imaging, as well as in haemochromatosis, thalassemia or cancer treatments. This Review offers insights into the diversity of siderophores, highlighting their potential applications in environmental and medical contexts.
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2
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Knejski PP, Erramilli SK, Kossiakoff AA. Chaperone-assisted cryo-EM structure of P. aeruginosa PhuR reveals molecular basis for heme binding. Structure 2024; 32:411-423.e6. [PMID: 38325368 PMCID: PMC10997469 DOI: 10.1016/j.str.2024.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Revised: 12/14/2023] [Accepted: 01/11/2024] [Indexed: 02/09/2024]
Abstract
Pathogenic bacteria, such as Pseudomonas aeruginosa, depend on scavenging heme for the acquisition of iron, an essential nutrient. The TonB-dependent transporter (TBDT) PhuR is the major heme uptake protein in P. aeruginosa clinical isolates. However, a comprehensive understanding of heme recognition and TBDT transport mechanisms, especially PhuR, remains limited. In this study, we employed single-particle cryogenic electron microscopy (cryo-EM) and a phage display-generated synthetic antibody (sAB) as a fiducial marker to enable the determination of a high-resolution (2.5 Å) structure of PhuR with a bound heme. Notably, the structure reveals iron coordination by Y529 on a conserved extracellular loop, shedding light on the role of tyrosine in heme binding. Biochemical assays and negative-stain EM demonstrated that the sAB specifically targets the heme-bound state of PhuR. These findings provide insights into PhuR's heme binding and offer a template for developing conformation-specific sABs against outer membrane proteins (OMPs) for structure-function investigations.
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Affiliation(s)
- Paweł P Knejski
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA; Laboratory of Medical Biology, Faculty of Biotechnology, University of Wrocław, 50-383 Wrocław, Poland
| | - Satchal K Erramilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
| | - Anthony A Kossiakoff
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA; Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA.
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3
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Yang T, Zou Y, Ng HL, Kumar A, Newton SM, Klebba PE. Specificity and mechanism of TonB-dependent ferric catecholate uptake by Fiu. Front Microbiol 2024; 15:1355253. [PMID: 38601941 PMCID: PMC11005823 DOI: 10.3389/fmicb.2024.1355253] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Accepted: 01/23/2024] [Indexed: 04/12/2024] Open
Abstract
We studied the Escherichia coli outer membrane protein Fiu, a presumed transporter of monomeric ferric catecholates, by introducing Cys residues in its surface loops and modifying them with fluorescein maleimide (FM). Fiu-FM bound iron complexes of the tricatecholate siderophore enterobactin (FeEnt) and glucosylated enterobactin (FeGEnt), their dicatecholate degradation product Fe(DHBS)2 (FeEnt*), the monocatecholates dihydroxybenzoic acid (FeDHBA) and dihydroxybenzoyl serine (FeDHBS), and the siderophore antibiotics cefiderocol (FDC) and MB-1. Unlike high-affinity ligand-gated porins (LGPs), Fiu-FM had only micromolar affinity for iron complexes. Its apparent KD values for FeDHBS, FeDHBA, FeEnt*, FeEnt, FeGEnt, FeFDC, and FeMB-1 were 0.1, 0.7, 0.7, 1.0, 0.3, 0.4, and 4 μM, respectively. Despite its broad binding abilities, the transport repertoires of E. coli Fiu, as well as those of Cir and FepA, were less broad. Fiu only transported FeEnt*. Cir transported FeEnt* and FeDHBS (weakly); FepA transported FeEnt, FeEnt*, and FeDHBA. Both Cir and FepA bound FeGEnt, albeit with lower affinity. Related transporters of Acinetobacter baumannii (PiuA, PirA, BauA) had similarly moderate affinity and broad specificity for di- or monomeric ferric catecholates. Both microbiological and radioisotopic experiments showed Fiu's exclusive transport of FeEnt*, rather than ferric monocatecholate compounds. Molecular docking and molecular dynamics simulations predicted three binding sites for FeEnt*in the external vestibule of Fiu, and a fourth site deeper in its interior. Alanine scanning mutagenesis in the outermost sites (1a, 1b, and 2) decreased FeEnt* binding affinity as much as 20-fold and reduced or eliminated FeEnt* uptake. Finally, the molecular dynamics simulations suggested a pathway of FeEnt* movement through Fiu that may generally describe the process of metal transport by TonB-dependent receptors.
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Affiliation(s)
| | | | | | | | | | - Phillip E. Klebba
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS, United States
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4
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Motz RN, Guo C, Sargun A, Walker GT, Sassone-Corsi M, Raffatellu M, Nolan EM. Conjugation to Native and Nonnative Triscatecholate Siderophores Enhances Delivery and Antibacterial Activity of a β-Lactam to Gram-Negative Bacterial Pathogens. J Am Chem Soc 2024; 146:7708-7722. [PMID: 38457782 PMCID: PMC11037102 DOI: 10.1021/jacs.3c14490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/10/2024]
Abstract
Developing new antibiotics and delivery strategies is of critical importance for treating infections caused by Gram-negative bacterial pathogens. Hijacking bacterial iron uptake machinery, such as that of the siderophore enterobactin (Ent), represents one promising approach toward these goals. Here, we report a novel Ent-inspired siderophore-antibiotic conjugate (SAC) employing an alternative siderophore moiety as the delivery vector and demonstrate the potency of our SACs harboring the β-lactam antibiotic ampicillin (Amp) against multiple pathogenic Gram-negative bacterial strains. We establish the ability of N,N',N''-(nitrilotris(ethane-2,1-diyl))tris(2,3-dihydroxybenzamide) (TRENCAM, hereafter TC), a synthetic mimic of Ent, to facilitate drug delivery across the outer membrane (OM) of Gram-negative pathogens. Conjugation of Amp to a new monofunctionalized TC scaffold affords TC-Amp, which displays markedly enhanced antibacterial activity against the gastrointestinal pathogen Salmonella enterica serovar Typhimurium (STm) compared with unmodified Amp. Bacterial uptake, antibiotic susceptibility, and microscopy studies with STm show that the TC moiety facilitates TC-Amp uptake by the OM receptors FepA and IroN and that the Amp warhead inhibits penicillin-binding proteins. Moreover, TC-Amp achieves targeted activity, selectively killing STm in the presence of a commensal lactobacillus. Remarkably, we uncover that TC-Amp and its Ent-based predecessor Ent-Amp achieve enhanced antibacterial activity against diverse Gram-negative ESKAPE pathogens that express Ent uptake machinery, including strains that possess intrinsic β-lactam resistance. TC-Amp and Ent-Amp exhibit potency comparable to that of the FDA-approved SAC cefiderocol against Gram-negative pathogens. These results demonstrate the effective application of native and appropriately designed nonnative siderophores as vectors for drug delivery across the OM of multiple Gram-negative bacterial pathogens.
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Affiliation(s)
- Rachel N. Motz
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Chuchu Guo
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Artur Sargun
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Gregory T. Walker
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California San Diego, La Jolla, CA 92093, USA
| | - Martina Sassone-Corsi
- Department of Microbiology & Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
| | - Manuela Raffatellu
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California San Diego, La Jolla, CA 92093, USA
- Department of Microbiology & Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
- Center for Microbiome Innovation, University of California San Diego, La Jolla, CA 92093, USA
- Chiba University-UC San Diego Center for Mucosal Immunology, Allergy, and Vaccines, La Jolla, CA 92093, USA
| | - Elizabeth M. Nolan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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5
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Schalk IJ, Perraud Q. Pseudomonas aeruginosa and its multiple strategies to access iron. Environ Microbiol 2022; 25:811-831. [PMID: 36571575 DOI: 10.1111/1462-2920.16328] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 12/21/2022] [Indexed: 12/27/2022]
Abstract
Pseudomonas aeruginosa is a ubiquitous bacterium found in many natural and man-made environments. It is also a pathogen for plants, animals, and humans. As for almost all living organisms, iron is an essential nutrient for the growth of P. aeruginosa. The bacterium has evolved complex systems to access iron and maintain its homeostasis to survive in diverse natural and dynamic host environments. To access ferric iron, P. aeruginosa is able to produce two siderophores (pyoverdine and pyochelin), as well as use a variety of siderophores produced by other bacteria (mycobactins, enterobactin, ferrioxamine, ferrichrome, vibriobactin, aerobactin, rhizobactin and schizokinen). Furthermore, it can also use citrate, in addition to catecholamine neuromediators and plant-derived mono catechols, as siderophores. The P. aeruginosa genome also encodes three heme-uptake pathways (heme being an iron source) and one ferrous iron acquisition pathway. This review aims to summarize current knowledge concerning the molecular mechanisms involved in all the iron and heme acquisition strategies used by P. aeruginosa.
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Affiliation(s)
- Isabelle J Schalk
- CNRS, UMR7242, ESBS, Strasbourg, France.,University of Strasbourg, UMR7242, ESBS, Strasbourg, France
| | - Quentin Perraud
- CNRS, UMR7242, ESBS, Strasbourg, France.,University of Strasbourg, UMR7242, ESBS, Strasbourg, France
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6
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Kumar A, Yang T, Chakravorty S, Majumdar A, Nairn BL, Six DA, Marcondes Dos Santos N, Price SL, Lawrenz MB, Actis LA, Marques M, Russo TA, Newton SM, Klebba PE. Fluorescent sensors of siderophores produced by bacterial pathogens. J Biol Chem 2022; 298:101651. [PMID: 35101443 PMCID: PMC8921320 DOI: 10.1016/j.jbc.2022.101651] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 11/25/2022] Open
Abstract
Siderophores are iron-chelating molecules that solubilize Fe3+ for microbial utilization and facilitate colonization or infection of eukaryotes by liberating host iron for bacterial uptake. By fluorescently labeling membrane receptors and binding proteins, we created 20 sensors that detect, discriminate, and quantify apo- and ferric siderophores. The sensor proteins originated from TonB-dependent ligand-gated porins (LGPs) of Escherichia coli (Fiu, FepA, Cir, FhuA, IutA, BtuB), Klebsiella pneumoniae (IroN, FepA, FyuA), Acinetobacter baumannii (PiuA, FepA, PirA, BauA), Pseudomonas aeruginosa (FepA, FpvA), and Caulobacter crescentus (HutA) from a periplasmic E. coli binding protein (FepB) and from a human serum binding protein (siderocalin). They detected ferric catecholates (enterobactin, degraded enterobactin, glucosylated enterobactin, dihydroxybenzoate, dihydroxybenzoyl serine, cefidericol, MB-1), ferric hydroxamates (ferrichromes, aerobactin), mixed iron complexes (yersiniabactin, acinetobactin, pyoverdine), and porphyrins (hemin, vitamin B12). The sensors defined the specificities and corresponding affinities of the LGPs and binding proteins and monitored ferric siderophore and porphyrin transport by microbial pathogens. We also quantified, for the first time, broad recognition of diverse ferric complexes by some LGPs, as well as monospecificity for a single metal chelate by others. In addition to their primary ferric siderophore ligands, most LGPs bound the corresponding aposiderophore with ∼100-fold lower affinity. These sensors provide insights into ferric siderophore biosynthesis and uptake pathways in free-living, commensal, and pathogenic Gram-negative bacteria.
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Affiliation(s)
- Ashish Kumar
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Taihao Yang
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Somnath Chakravorty
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA; Department of Medicine, Jacobs School of Medicine & Biomedical Sciences, University of Buffalo School of Medicine, Buffalo, New York, USA
| | - Aritri Majumdar
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Brittany L Nairn
- Department of Biological Sciences, Bethel University, St. Paul, Minnesota, USA
| | - David A Six
- Department of Biology, Venatorx Pharmaceuticals, Inc, Malvern, Pennsylvania, USA
| | - Naara Marcondes Dos Santos
- Departamento de Microbiologia, Instituto de Ciencias Biomedicas, Universidade de São Paulo, São Paulo, Brazil
| | - Sarah L Price
- Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, Kentucky, USA
| | - Matthew B Lawrenz
- Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, Kentucky, USA
| | - Luis A Actis
- Department of Microbiology, Miami University, Oxford, Ohio, USA
| | - Marilis Marques
- Departamento de Microbiologia, Instituto de Ciencias Biomedicas, Universidade de São Paulo, São Paulo, Brazil
| | - Thomas A Russo
- Department of Medicine, Jacobs School of Medicine & Biomedical Sciences, University of Buffalo School of Medicine, Buffalo, New York, USA
| | - Salete M Newton
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Phillip E Klebba
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA.
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7
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Klebba PE, Newton SMC, Six DA, Kumar A, Yang T, Nairn BL, Munger C, Chakravorty S. Iron Acquisition Systems of Gram-negative Bacterial Pathogens Define TonB-Dependent Pathways to Novel Antibiotics. Chem Rev 2021; 121:5193-5239. [PMID: 33724814 PMCID: PMC8687107 DOI: 10.1021/acs.chemrev.0c01005] [Citation(s) in RCA: 58] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Iron is an indispensable metabolic cofactor in both pro- and eukaryotes, which engenders a natural competition for the metal between bacterial pathogens and their human or animal hosts. Bacteria secrete siderophores that extract Fe3+ from tissues, fluids, cells, and proteins; the ligand gated porins of the Gram-negative bacterial outer membrane actively acquire the resulting ferric siderophores, as well as other iron-containing molecules like heme. Conversely, eukaryotic hosts combat bacterial iron scavenging by sequestering Fe3+ in binding proteins and ferritin. The variety of iron uptake systems in Gram-negative bacterial pathogens illustrates a range of chemical and biochemical mechanisms that facilitate microbial pathogenesis. This document attempts to summarize and understand these processes, to guide discovery of immunological or chemical interventions that may thwart infectious disease.
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Affiliation(s)
- Phillip E Klebba
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Salete M C Newton
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - David A Six
- Venatorx Pharmaceuticals, Inc., 30 Spring Mill Drive, Malvern, Pennsylvania 19355, United States
| | - Ashish Kumar
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Taihao Yang
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Brittany L Nairn
- Department of Biological Sciences, Bethel University, 3900 Bethel Drive, St. Paul, Minnesota 55112, United States
| | - Colton Munger
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Somnath Chakravorty
- Jacobs School of Medicine and Biomedical Sciences, SUNY Buffalo, Buffalo, New York 14203, United States
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8
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Majumdar A, Trinh V, Moore KJ, Smallwood CR, Kumar A, Yang T, Scott DC, Long NJ, Newton SM, Klebba PE. Conformational rearrangements in the N-domain of Escherichia coli FepA during ferric enterobactin transport. J Biol Chem 2020; 295:4974-4984. [PMID: 32098871 DOI: 10.1074/jbc.ra119.011850] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/14/2020] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli outer membrane receptor FepA transports ferric enterobactin (FeEnt) by an energy- and TonB-dependent, but otherwise a mechanistically undetermined process involving its internal 150-residue N-terminal globular domain (N-domain). We genetically introduced pairs of Cys residues in different regions of the FepA tertiary structure, with the potential to form disulfide bonds. These included Cys pairs on adjacent β-strands of the N-domain (intra-N) and Cys pairs that bridged the external surface of the N-domain to the interior of the C-terminal transmembrane β-barrel (inter-N-C). We characterized FeEnt uptake by these mutants with siderophore nutrition tests, [59Fe]Ent binding and uptake experiments, and fluorescence decoy sensor assays. The three methods consistently showed that the intra-N disulfide bonds, which restrict conformational motion within the N-domain, prevented FeEnt uptake, whereas most inter-N-C disulfide bonds did not prevent FeEnt uptake. These outcomes indicate that conformational rearrangements must occur in the N terminus of FepA during FeEnt transport. They also argue against disengagement of the N-domain out of the channel as a rigid body and suggest instead that it remains within the transmembrane pore as FeEnt enters the periplasm.
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Affiliation(s)
- Aritri Majumdar
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Vy Trinh
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Kyle J Moore
- Department of Chemistry, Physics and Engineering, Cameron University, Lawton, Oklahoma 73505
| | | | - Ashish Kumar
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Taihao Yang
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Daniel C Scott
- Howard Hughes Medical Institute, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Noah J Long
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Salete M Newton
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Phillip E Klebba
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
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9
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Moynié L, Milenkovic S, Mislin GLA, Gasser V, Malloci G, Baco E, McCaughan RP, Page MGP, Schalk IJ, Ceccarelli M, Naismith JH. The complex of ferric-enterobactin with its transporter from Pseudomonas aeruginosa suggests a two-site model. Nat Commun 2019; 10:3673. [PMID: 31413254 PMCID: PMC6694100 DOI: 10.1038/s41467-019-11508-y] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 07/16/2019] [Indexed: 11/17/2022] Open
Abstract
Bacteria use small molecules called siderophores to scavenge iron. Siderophore-Fe3+ complexes are recognised by outer-membrane transporters and imported into the periplasm in a process dependent on the inner-membrane protein TonB. The siderophore enterobactin is secreted by members of the family Enterobacteriaceae, but many other bacteria including Pseudomonas species can use it. Here, we show that the Pseudomonas transporter PfeA recognises enterobactin using extracellular loops distant from the pore. The relevance of this site is supported by in vivo and in vitro analyses. We suggest there is a second binding site deeper inside the structure and propose that correlated changes in hydrogen bonds link binding-induced structural re-arrangements to the structural adjustment of the periplasmic TonB-binding motif.
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Affiliation(s)
- Lucile Moynié
- Division of Structural Biology, Wellcome Trust Centre of Human Genomics, 7 Roosevelt Drive, Oxford, OX3 7BN, UK
- The Research Complex at Harwell, Harwell Campus, Oxfordshire, OX11 0FA, UK
- The Rosalind Franklin Institute, Didcot, OX11 0FA, UK
| | - Stefan Milenkovic
- Department of Physics, University of Cagliari, Cittadella Universitaria, SP Monserrato-Sestu Km 0.700, Monserrato, 09042, Italy
| | - Gaëtan L A Mislin
- Université de Strasbourg, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
- CNRS, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
| | - Véronique Gasser
- Université de Strasbourg, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
- CNRS, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
| | - Giuliano Malloci
- Department of Physics, University of Cagliari, Cittadella Universitaria, SP Monserrato-Sestu Km 0.700, Monserrato, 09042, Italy
| | - Etienne Baco
- Université de Strasbourg, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
- CNRS, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France
| | | | - Malcolm G P Page
- Department of Life Sciences & Chemistry, Campus Ring 1, Bremen, 28759, Germany
| | - Isabelle J Schalk
- Université de Strasbourg, UMR7242, ESBS, Bld Sébastien Brant, Illkirch, F-67413, Strasbourg, France.
- Istituto Officina dei Materiali-CNR, Cittadella Universitaria, Monserrato, 09042, Italy.
| | - Matteo Ceccarelli
- Department of Physics, University of Cagliari, Cittadella Universitaria, SP Monserrato-Sestu Km 0.700, Monserrato, 09042, Italy.
- Istituto Officina dei Materiali-CNR, Cittadella Universitaria, Monserrato, 09042, Italy.
| | - James H Naismith
- Division of Structural Biology, Wellcome Trust Centre of Human Genomics, 7 Roosevelt Drive, Oxford, OX3 7BN, UK.
- The Research Complex at Harwell, Harwell Campus, Oxfordshire, OX11 0FA, UK.
- The Rosalind Franklin Institute, Didcot, OX11 0FA, UK.
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10
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Moynié L, Serra I, Scorciapino MA, Oueis E, Page MG, Ceccarelli M, Naismith JH. Preacinetobactin not acinetobactin is essential for iron uptake by the BauA transporter of the pathogen Acinetobacter baumannii. eLife 2018; 7:42270. [PMID: 30558715 PMCID: PMC6300358 DOI: 10.7554/elife.42270] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Accepted: 12/02/2018] [Indexed: 01/05/2023] Open
Abstract
New strategies are urgently required to develop antibiotics. The siderophore uptake system has attracted considerable attention, but rational design of siderophore antibiotic conjugates requires knowledge of recognition by the cognate outer-membrane transporter. Acinetobacter baumannii is a serious pathogen, which utilizes (pre)acinetobactin to scavenge iron from the host. We report the structure of the (pre)acinetobactin transporter BauA bound to the siderophore, identifying the structural determinants of recognition. Detailed biophysical analysis confirms that BauA recognises preacinetobactin. We show that acinetobactin is not recognised by the protein, thus preacinetobactin is essential for iron uptake. The structure shows and NMR confirms that under physiological conditions, a molecule of acinetobactin will bind to two free coordination sites on the iron preacinetobactin complex. The ability to recognise a heterotrimeric iron-preacinetobactin-acinetobactin complex may rationalize contradictory reports in the literature. These results open new avenues for the design of novel antibiotic conjugates (trojan horse) antibiotics.
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Affiliation(s)
- Lucile Moynié
- Division of Structural Biology, Wellcome Trust Centre of Human Genomics, Oxford, England.,Research Complex at Harwell, Rutherford Laboratory, Didcot, England
| | - Ilaria Serra
- Department of Physics, University of Cagliari, Cagliari, Italy.,Department of Chemical and Geological Sciences, University of Cagliari, Cagliari, Italy
| | - Mariano A Scorciapino
- Department of Physics, University of Cagliari, Cagliari, Italy.,Department of Chemical and Geological Sciences, University of Cagliari, Cagliari, Italy
| | - Emilia Oueis
- Biomedical Sciences Research Complex, The University of St Andrews, Scotland, United Kingdom
| | - Malcolm Gp Page
- Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany
| | | | - James H Naismith
- Division of Structural Biology, Wellcome Trust Centre of Human Genomics, Oxford, England.,Research Complex at Harwell, Rutherford Laboratory, Didcot, England.,The Rosalind Franklin Institute, Didcot, England
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11
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Luscher A, Moynié L, Auguste PS, Bumann D, Mazza L, Pletzer D, Naismith JH, Köhler T. TonB-Dependent Receptor Repertoire of Pseudomonas aeruginosa for Uptake of Siderophore-Drug Conjugates. Antimicrob Agents Chemother 2018; 62:e00097-18. [PMID: 29555629 PMCID: PMC5971595 DOI: 10.1128/aac.00097-18] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 03/12/2018] [Indexed: 12/22/2022] Open
Abstract
The conjugation of siderophores to antimicrobial molecules is an attractive strategy to overcome the low outer membrane permeability of Gram-negative bacteria. In this Trojan horse approach, the transport of drug conjugates is redirected via TonB-dependent receptors (TBDR), which are involved in the uptake of essential nutrients, including iron. Previous reports have demonstrated the involvement of the TBDRs PiuA and PirA from Pseudomonas aeruginosa and their orthologues in Acinetobacter baumannii in the uptake of siderophore-beta-lactam drug conjugates. By in silico screening, we further identified a PiuA orthologue, termed PiuD, present in clinical isolates, including strain LESB58. The piuD gene in LESB58 is located at the same genetic locus as piuA in strain PAO1. PiuD has a similar crystal structure as PiuA and is involved in the transport of the siderophore-drug conjugates BAL30072, MC-1, and cefiderocol in strain LESB58. To screen for additional siderophore-drug uptake systems, we overexpressed 28 of the 34 TBDRs of strain PAO1 and identified PfuA, OptE, OptJ, and the pyochelin receptor FptA as novel TBDRs conferring increased susceptibility to siderophore-drug conjugates. The existence of a TBDR repertoire in P. aeruginosa able to transport siderophore-drug molecules potentially decreases the likelihood of resistance emergence during therapy.
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Affiliation(s)
- Alexandre Luscher
- Service of Infectious Diseases, University Hospital Geneva, Geneva, Switzerland
- Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland
| | - Lucile Moynié
- School of Chemistry and Biomedical Sciences Research Complex, University of St Andrews, Fife, Scotland, United Kingdom
| | | | - Dirk Bumann
- Biozentrum, University of Basel, Basel, Switzerland
| | - Lena Mazza
- Service of Infectious Diseases, University Hospital Geneva, Geneva, Switzerland
- Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland
| | | | - James H Naismith
- School of Chemistry and Biomedical Sciences Research Complex, University of St Andrews, Fife, Scotland, United Kingdom
| | - Thilo Köhler
- Service of Infectious Diseases, University Hospital Geneva, Geneva, Switzerland
- Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland
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12
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Structure and Function of the PiuA and PirA Siderophore-Drug Receptors from Pseudomonas aeruginosa and Acinetobacter baumannii. Antimicrob Agents Chemother 2017; 61:AAC.02531-16. [PMID: 28137795 DOI: 10.1128/aac.02531-16] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 01/27/2017] [Indexed: 01/06/2023] Open
Abstract
The outer membrane of Gram-negative bacteria presents an efficient barrier to the permeation of antimicrobial molecules. One strategy pursued to circumvent this obstacle is to hijack transport systems for essential nutrients, such as iron. BAL30072 and MC-1 are two monobactams conjugated to a dihydroxypyridone siderophore that are active against Pseudomonas aeruginosa and Acinetobacter baumannii Here, we investigated the mechanism of action of these molecules in A. baumannii We identified two novel TonB-dependent receptors, termed Ab-PiuA and Ab-PirA, that are required for the antimicrobial activity of both agents. Deletion of either piuA or pirA in A. baumannii resulted in 4- to 8-fold-decreased susceptibility, while their overexpression in the heterologous host P. aeruginosa increased susceptibility to the two siderophore-drug conjugates by 4- to 32-fold. The crystal structures of PiuA and PirA from A. baumannii and their orthologues from P. aeruginosa were determined. The structures revealed similar architectures; however, structural differences between PirA and PiuA point to potential differences between their cognate siderophore ligands. Spontaneous mutants, selected upon exposure to BAL30072, harbored frameshift mutations in either the ExbD3 or the TonB3 protein of A. baumannii, forming the cytoplasmic-membrane complex providing the energy for the siderophore translocation process. The results of this study provide insight for the rational design of novel siderophore-drug conjugates against problematic Gram-negative pathogens.
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13
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TonB-dependent ligand trapping in the BtuB transporter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:3105-3112. [DOI: 10.1016/j.bbamem.2016.09.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 09/21/2016] [Accepted: 09/22/2016] [Indexed: 11/22/2022]
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14
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Smallwood CR, Jordan L, Trinh V, Schuerch DW, Gala A, Hanson M, Hanson M, Shipelskiy Y, Majumdar A, Newton SMC, Klebba PE. Concerted loop motion triggers induced fit of FepA to ferric enterobactin. ACTA ACUST UNITED AC 2015; 144:71-80. [PMID: 24981231 PMCID: PMC4076525 DOI: 10.1085/jgp.201311159] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The loops of the bacterial outer membrane iron transporter FepA move at different rates to adsorb and grasp the substrate ferric enterobactin before transporting it into the periplasm. Spectroscopic analyses of fluorophore-labeled Escherichia coli FepA described dynamic actions of its surface loops during binding and transport of ferric enterobactin (FeEnt). When FeEnt bound to fluoresceinated FepA, in living cells or outer membrane fragments, quenching of fluorophore emissions reflected conformational motion of the external vestibular loops. We reacted Cys sulfhydryls in seven surface loops (L2, L3, L4, L5, L7 L8, and L11) with fluorophore maleimides. The target residues had different accessibilities, and the labeled loops themselves showed variable extents of quenching and rates of motion during ligand binding. The vestibular loops closed around FeEnt in about a second, in the order L3 > L11 > L7 > L2 > L5 > L8 > L4. This sequence suggested that the loops bind the metal complex like the fingers of two hands closing on an object, by individually adsorbing to the iron chelate. Fluorescence from L3 followed a biphasic exponential decay as FeEnt bound, but fluorescence from all the other loops followed single exponential decay processes. After binding, the restoration of fluorescence intensity (from any of the labeled loops) mirrored cellular uptake that depleted FeEnt from solution. Fluorescence microscopic images also showed FeEnt transport, and demonstrated that ferric siderophore uptake uniformly occurs throughout outer membrane, including at the poles of the cells, despite the fact that TonB, its inner membrane transport partner, was not detectable at the poles.
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Affiliation(s)
- Chuck R Smallwood
- The Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019
| | - Lorne Jordan
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
| | - Vy Trinh
- The Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019
| | - Daniel W Schuerch
- The Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019
| | - Amparo Gala
- The Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019
| | - Mathew Hanson
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
| | | | - Yan Shipelskiy
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
| | - Aritri Majumdar
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
| | - Salete M C Newton
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
| | - Phillip E Klebba
- The Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506
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15
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Schalk IJ, Mislin GLA, Brillet K. Structure, function and binding selectivity and stereoselectivity of siderophore-iron outer membrane transporters. CURRENT TOPICS IN MEMBRANES 2012; 69:37-66. [PMID: 23046646 DOI: 10.1016/b978-0-12-394390-3.00002-1] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
To get access to iron, microorganisms produce and release into their environment small organic metal chelators called siderophores. In parallel, they produce siderophore-iron outer membrane transporters (also called TonB-Dependent Transporters or TBDT) embedded in the outer membrane; these proteins actively reabsorb the siderophore loaded with iron from the extracellular medium. This active uptake requires energy in the form of the proton motive force transferred from the inner membrane to the outer membrane transporter via the inner membrane TonB complex. Siderophores produced by microorganisms are structurally very diverse with molecular weights of 150 up to 2000Da. Siderophore-iron uptake from the extracellular medium by TBDTs is a highly selective and sometimes even stereoselective process, with each siderophore having a specific TBDT. Unlike the siderophores, all TBDTs have similar structures and belong to the outer membrane β-barrel protein superfamily. The way in which the siderophore-iron complex passes through the TBDT is still unclear. In some bacteria, TBDTs are also partners of signaling cascades regulating the expression of proteins involved in siderophore biosynthesis and siderophore-iron acquisition.
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Affiliation(s)
- Isabelle J Schalk
- UMR 7242, Université de Strasbourg-CNRS, ESBS, Boulevard Sébastien Brant, Strasbourg, France.
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16
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Newton SM, Trinh V, Pi H, Klebba PE. Direct measurements of the outer membrane stage of ferric enterobactin transport: postuptake binding. J Biol Chem 2010; 285:17488-97. [PMID: 20335169 PMCID: PMC2878513 DOI: 10.1074/jbc.m109.100206] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2010] [Revised: 02/23/2010] [Indexed: 11/06/2022] Open
Abstract
When Gram-negative bacteria acquire iron, the metal crosses both the outer membrane (OM) and the inner membrane, but existing radioisotopic uptake assays only measure its passage through the latter bilayer, as the accumulation of the radionuclide in the cytoplasm. We devised a methodology that exclusively observes OM transport and used it to study the uptake of ferric enterobactin (FeEnt) by Escherichia coli FepA. This technique, called postuptake binding, revealed previously unknown aspects of TonB-dependent transport reactions. The experiments showed, for the first time, that despite the discrepancy in cell envelope concentrations of FepA and TonB ( approximately 35:1), all FepA proteins were active and equivalent in FeEnt uptake, with a maximum turnover number of approximately 5/min. FepA-mediated transport of FeEnt progressed through three distinct phases with successively decreasing rates, and from its temperature dependence, the activation energy of the OM stage was 33-35 kcal/mol. The accumulation of FeEnt in the periplasm required the binding protein and inner membrane permease components of its overall transport system; postuptake binding assays on strains devoid of FepB, FepD, or FepG did not show uptake of FeEnt through the OM. However, fluorescence labeling data implied that FepA was active in the DeltafepB strain, suggesting that FeEnt entered the periplasm but then leaked out. Further experiments confirmed this futile cycle; cells without FepB transported FeEnt across the OM, but it immediately escaped through TolC.
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Affiliation(s)
- Salete M. Newton
- From the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Vy Trinh
- From the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Hualiang Pi
- From the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Phillip E. Klebba
- From the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
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17
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Lim BL. TonB-Dependent Receptors in Nitrogen-Fixing Nodulating Bacteria. Microbes Environ 2010; 25:67-74. [DOI: 10.1264/jsme2.me10102] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Boon L. Lim
- School of Biological Sciences, University of Hong Kong
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18
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Smallwood CR, Marco AG, Xiao Q, Trinh V, Newton SMC, Klebba PE. Fluoresceination of FepA during colicin B killing: effects of temperature, toxin and TonB. Mol Microbiol 2009; 72:1171-80. [PMID: 19432807 PMCID: PMC3082853 DOI: 10.1111/j.1365-2958.2009.06715.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We studied the reactivity of 35 genetically engineered Cys sulphydryl groups at different locations in Escherichia coli FepA. Modification of surface loop residues by fluorescein maleimide (FM) was strongly temperature-dependent in vivo, whereas reactivity at other sites was much less affected. Control reactions with bovine serum albumin showed that the temperature dependence of loop residue reactivity was unusually high, indicating that conformational changes in multiple loops (L2, L3, L4, L5, L7, L8, L10) transform the receptor to a more accessible form at 37 degrees C. At 0 degrees C colicin B binding impaired or blocked labelling at 8 of 10 surface loop sites, presumably by steric hindrance. Overall, colicin B adsorption decreased the reactivity of more than half of the 35 sites, in both the N- and C- domains of FepA. However, colicin B penetration into the cell at 37 degrees C did not augment the chemical modification of any residues in FepA. The FM modification patterns were similarly unaffected by the tonB locus. FepA was expressed at lower levels in a tonB host strain, but when we accounted for this decrease its FM labelling was comparable whether TonB was present or absent. Thus we did not detect TonB-dependent structural changes in FepA, either alone or when it interacted with colicin B at 37 degrees C. The only changes in chemical modification were reductions from steric hindrance when the bacteriocin bound to the receptor protein. The absence of increases in the reactivity of N-domain residues argues against the idea that the colicin B polypeptide traverses the FepA channel.
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Affiliation(s)
| | | | - Qiaobin Xiao
- The Department of Chemistry & Biochemistry University of Oklahoma, Norman OK 73019
| | - Vy Trinh
- The Department of Chemistry & Biochemistry University of Oklahoma, Norman OK 73019
| | - Salete M. C. Newton
- The Department of Chemistry & Biochemistry University of Oklahoma, Norman OK 73019
| | - Phillip E. Klebba
- The Department of Chemistry & Biochemistry University of Oklahoma, Norman OK 73019
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19
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Schauer K, Rodionov DA, de Reuse H. New substrates for TonB-dependent transport: do we only see the 'tip of the iceberg'? Trends Biochem Sci 2008; 33:330-8. [PMID: 18539464 DOI: 10.1016/j.tibs.2008.04.012] [Citation(s) in RCA: 254] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 04/04/2008] [Accepted: 04/08/2008] [Indexed: 11/26/2022]
Abstract
TonB-dependent transport is a mechanism for active uptake across the outer membrane of Gram-negative bacteria. The system promotes transport of rare nutrients and was thought to be restricted to iron complexes and vitamin B12. Recent experimental evidence of TonB-energized transport of nickel and different carbohydrates, in addition to bioinformatic-based predictions, challenges this notion and reveals that the number and variety of TonB-dependent substrates is underestimated. It is becoming clear that the chemical nature of the substrates, the energetic requirements for transport and the subsequent translocation across the cytoplasmic membrane can differ from those of the well-studied systems for iron complexes and vitamin B12. These findings question the understanding of TonB-dependent uptake and provide insights into the adaptation of bacteria to their environments.
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Affiliation(s)
- Kristine Schauer
- Institut Pasteur, Unité Postulante de Pathogenèse de Helicobacter, Département de Microbiologie, 75724 Paris Cedex 15, France.
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20
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Schalk IJ. Metal trafficking via siderophores in Gram-negative bacteria: Specificities and characteristics of the pyoverdine pathway. J Inorg Biochem 2008; 102:1159-69. [DOI: 10.1016/j.jinorgbio.2007.11.017] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 10/03/2007] [Accepted: 11/30/2007] [Indexed: 10/22/2022]
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21
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Insight from TonB hybrid proteins into the mechanism of iron transport through the outer membrane. J Bacteriol 2008; 190:4001-16. [PMID: 18390658 DOI: 10.1128/jb.00135-08] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We created hybrid proteins to study the functions of TonB. We first fused the portion of Escherichia coli tonB that encodes the C-terminal 69 amino acids (amino acids 170 to 239) of TonB downstream from E. coli malE (MalE-TonB69C). Production of MalE-TonB69C in tonB(+) bacteria inhibited siderophore transport. After overexpression and purification of the fusion protein on an amylose column, we proteolytically released the TonB C terminus and characterized it. Fluorescence spectra positioned its sole tryptophan (W213) in a weakly polar site in the protein interior, shielded from quenchers. Affinity chromatography showed the binding of the TonB C-domain to other proteins: immobilized TonB-dependent (FepA and colicin B) and TonB-independent (FepADelta3-17, OmpA, and lysozyme) proteins adsorbed MalE-TonB69C, revealing a general affinity of the C terminus for other proteins. Additional constructions fused full-length TonB upstream or downstream of green fluorescent protein (GFP). TonB-GFP constructs had partial functionality but no fluorescence; GFP-TonB fusion proteins were functional and fluorescent. The activity of the latter constructs, which localized GFP in the cytoplasm and TonB in the cell envelope, indicate that the TonB N terminus remains in the inner membrane during its biological function. Finally, sequence analyses revealed homology in the TonB C terminus to E. coli YcfS, a proline-rich protein that contains the lysin (LysM) peptidoglycan-binding motif. LysM structural mimicry occurs in two positions of the dimeric TonB C-domain, and experiments confirmed that it physically binds to the murein sacculus. Together, these findings infer that the TonB N terminus remains associated with the inner membrane, while the downstream region bridges the cell envelope from the affinity of the C terminus for peptidoglycan. This architecture suggests a membrane surveillance model of action, in which TonB finds occupied receptor proteins by surveying the underside of peptidoglycan-associated outer membrane proteins.
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22
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Abstract
High-affinity iron acquisition is mediated by siderophore-dependent pathways in the majority of pathogenic and nonpathogenic bacteria and fungi. Considerable progress has been made in characterizing and understanding mechanisms of siderophore synthesis, secretion, iron scavenging, and siderophore-delivered iron uptake and its release. The regulation of siderophore pathways reveals multilayer networks at the transcriptional and posttranscriptional levels. Due to the key role of many siderophores during virulence, coevolution led to sophisticated strategies of siderophore neutralization by mammals and (re)utilization by bacterial pathogens. Surprisingly, hosts also developed essential siderophore-based iron delivery and cell conversion pathways, which are of interest for diagnostic and therapeutic studies. In the last decades, natural and synthetic compounds have gained attention as potential therapeutics for iron-dependent treatment of infections and further diseases. Promising results for pathogen inhibition were obtained with various siderophore-antibiotic conjugates acting as "Trojan horse" toxins and siderophore pathway inhibitors. In this article, general aspects of siderophore-mediated iron acquisition, recent findings regarding iron-related pathogen-host interactions, and current strategies for iron-dependent pathogen control will be reviewed. Further concepts including the inhibition of novel siderophore pathway targets are discussed.
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Affiliation(s)
- Marcus Miethke
- Philipps Universität Marburg, FB Chemie Biochemie, Hans Meerwein Strasse, D-35032 Marburg, Germany
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23
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Rabsch W, Ma L, Wiley G, Najar FZ, Kaserer W, Schuerch DW, Klebba JE, Roe BA, Laverde Gomez JA, Schallmey M, Newton SMC, Klebba PE. FepA- and TonB-dependent bacteriophage H8: receptor binding and genomic sequence. J Bacteriol 2007; 189:5658-74. [PMID: 17526714 PMCID: PMC1951831 DOI: 10.1128/jb.00437-07] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2007] [Accepted: 05/10/2007] [Indexed: 11/20/2022] Open
Abstract
H8 is derived from a collection of Salmonella enterica serotype Enteritidis bacteriophage. Its morphology and genomic structure closely resemble those of bacteriophage T5 in the family Siphoviridae. H8 infected S. enterica serotypes Enteritidis and Typhimurium and Escherichia coli by initial adsorption to the outer membrane protein FepA. Ferric enterobactin inhibited H8 binding to E. coli FepA (50% inhibition concentration, 98 nM), and other ferric catecholate receptors (Fiu, Cir, and IroN) did not participate in phage adsorption. H8 infection was TonB dependent, but exbB mutations in Salmonella or E. coli did not prevent infection; only exbB tolQ or exbB tolR double mutants were resistant to H8. Experiments with deletion and substitution mutants showed that the receptor-phage interaction first involves residues distributed over the protein's outer surface and then narrows to the same charged (R316) or aromatic (Y260) residues that participate in the binding and transport of ferric enterobactin and colicins B and D. These data rationalize the multifunctionality of FepA: toxic ligands like bacteriocins and phage penetrate the outer membrane by parasitizing residues in FepA that are adapted to the transport of the natural ligand, ferric enterobactin. DNA sequence determinations revealed the complete H8 genome of 104.4 kb. A total of 120 of its 143 predicted open reading frames (ORFS) were homologous to ORFS in T5, at a level of 84% identity and 89% similarity. As in T5, the H8 structural genes clustered on the chromosome according to their function in the phage life cycle. The T5 genome contains a large section of DNA that can be deleted and that is absent in H8: compared to T5, H8 contains a 9,000-bp deletion in the early region of its chromosome, and nine potentially unique gene products. Sequence analyses of the tail proteins of phages in the same family showed that relative to pb5 (Oad) of T5 and Hrs of BF23, the FepA-binding protein (Rbp) of H8 contains unique acidic and aromatic residues. These side chains may promote binding to basic and aromatic residues in FepA that normally function in the adsorption of ferric enterobactin. Furthermore, a predicted H8 tail protein showed extensive identity and similarity to pb2 of T5, suggesting that it also functions in pore formation through the cell envelope. The variable region of this protein contains a potential TonB box, intimating that it participates in the TonB-dependent stage of the phage infection process.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution
- Antiviral Agents/pharmacology
- Bacterial Outer Membrane Proteins/genetics
- Bacterial Outer Membrane Proteins/physiology
- Bacterial Proteins/genetics
- Bacterial Proteins/physiology
- Carrier Proteins/genetics
- Carrier Proteins/physiology
- DNA, Viral/chemistry
- DNA, Viral/genetics
- Enterobactin/pharmacology
- Escherichia coli/virology
- Gene Order
- Genome, Viral/genetics
- Membrane Proteins/genetics
- Membrane Proteins/physiology
- Microscopy, Electron, Transmission
- Models, Molecular
- Molecular Sequence Data
- Open Reading Frames
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/physiology
- Receptors, Virus/genetics
- Receptors, Virus/physiology
- Salmonella Phages/genetics
- Salmonella Phages/physiology
- Salmonella enteritidis/virology
- Salmonella typhimurium/virology
- Sequence Analysis, DNA
- Sequence Deletion
- Sequence Homology, Amino Acid
- Siphoviridae/genetics
- Viral Tail Proteins/genetics
- Virion/ultrastructure
- Virus Attachment
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Affiliation(s)
- Wolfgang Rabsch
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA
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24
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Pero JK, Haas EM, Thompson NL. Size dependence of protein diffusion very close to membrane surfaces: measurement by total internal reflection with fluorescence correlation spectroscopy. J Phys Chem B 2007; 110:10910-8. [PMID: 16771344 DOI: 10.1021/jp056990y] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The diffusion coefficients of nine fluorescently labeled antibodies, antibody fragments, and antibody complexes have been measured in solution very close to supported planar membranes by using total internal reflection with fluorescence correlation spectroscopy (TIR-FCS). The hydrodynamic radii (3-24 nm) of the nine antibody types were determined by comparing literature values with bulk diffusion coefficients measured by spot FCS. The diffusion coefficients very near membranes decreased significantly with molecular size, and the size dependence was greater than that predicted to occur in bulk solution. The observation that membrane surfaces slow the local diffusion coefficient of proteins in a size-dependent manner suggests that the primary effect is hydrodynamic as predicted for simple spheres diffusing close to planar walls. The TIR-FCS data are consistent with predictions derived from hydrodynamic theory. This work illustrates one factor that could contribute to previously observed nonideal ligand-receptor kinetics at model and natural cell membranes.
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Affiliation(s)
- Jamie K Pero
- Department of Chemistry, Campus Box 3290, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA
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25
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Cascales E, Buchanan SK, Duché D, Kleanthous C, Lloubès R, Postle K, Riley M, Slatin S, Cavard D. Colicin biology. Microbiol Mol Biol Rev 2007; 71:158-229. [PMID: 17347522 PMCID: PMC1847374 DOI: 10.1128/mmbr.00036-06] [Citation(s) in RCA: 784] [Impact Index Per Article: 46.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Colicins are proteins produced by and toxic for some strains of Escherichia coli. They are produced by strains of E. coli carrying a colicinogenic plasmid that bears the genetic determinants for colicin synthesis, immunity, and release. Insights gained into each fundamental aspect of their biology are presented: their synthesis, which is under SOS regulation; their release into the extracellular medium, which involves the colicin lysis protein; and their uptake mechanisms and modes of action. Colicins are organized into three domains, each one involved in a different step of the process of killing sensitive bacteria. The structures of some colicins are known at the atomic level and are discussed. Colicins exert their lethal action by first binding to specific receptors, which are outer membrane proteins used for the entry of specific nutrients. They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system. The components of each system are known, and their implication in the functioning of the system is described. Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA. The mechanisms of inhibition by specific and cognate immunity proteins are presented. Finally, the use of colicins as laboratory or biotechnological tools and their mode of evolution are discussed.
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Affiliation(s)
- Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires,Institut de Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, UPR 9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
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26
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Ma L, Kaserer W, Annamalai R, Scott DC, Jin B, Jiang X, Xiao Q, Maymani H, Massis LM, Ferreira LCS, Newton SMC, Klebba PE. Evidence of ball-and-chain transport of ferric enterobactin through FepA. J Biol Chem 2006; 282:397-406. [PMID: 17056600 PMCID: PMC2398697 DOI: 10.1074/jbc.m605333200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli iron transporter, FepA, has a globular N terminus that resides within a transmembrane beta-barrel formed by its C terminus. We engineered 25 cysteine substitution mutations at different locations in FepA and modified their sulfhydryl side chains with fluorescein maleimide in live cells. The reactivity of the Cys residues changed, sometimes dramatically, during the transport of ferric enterobactin, the natural ligand of FepA. Patterns of Cys susceptibility reflected energy- and TonB-dependent motion in the receptor protein. During transport, a residue on the normally buried surface of the N-domain was labeled by fluorescein maleimide in the periplasm, providing evidence that the transport process involves expulsion of the globular domain from the beta-barrel. Porin deficiency much reduced the fluoresceination of this site, confirming the periplasmic labeling route. These data support the previously proposed, but never demonstrated, ball-and-chain theory of membrane transport. Functional complementation between a separately expressed N terminus and C-terminal beta-barrel domain confirmed the feasibility of this mechanism.
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Affiliation(s)
- Li Ma
- Department of Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
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Destoumieux-Garzón D, Duquesne S, Peduzzi J, Goulard C, Desmadril M, Letellier L, Rebuffat S, Boulanger P. The iron-siderophore transporter FhuA is the receptor for the antimicrobial peptide microcin J25: role of the microcin Val11-Pro16 beta-hairpin region in the recognition mechanism. Biochem J 2005; 389:869-76. [PMID: 15862112 PMCID: PMC1180738 DOI: 10.1042/bj20042107] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The role of the outer-membrane iron transporter FhuA as a potential receptor for the antimicrobial peptide MccJ25 (microcin J25) was studied through a series of in vivo and in vitro experiments. The requirement for both FhuA and the inner-membrane TonB-ExbB-ExbD complex was demonstrated by antibacterial assays using complementation of an fhuA(-) strain and by using isogenic strains mutated in genes encoding the protein complex respectively. In addition, MccJ25 was shown to block phage T5 infection of Escherichia coli, in vivo, by inhibiting phage adhesion, which suggested that MccJ25 prevents the interaction between the phage and its receptor FhuA. This in vivo activity was confirmed in vitro, as MccJ25 inhibited phage T5 DNA ejection triggered by purified FhuA. Direct interaction of MccJ25 with FhuA was demonstrated for the first time by size-exclusion chromatography and isothermal titration calorimetry. MccJ25 bound to FhuA with a 2:1 stoichiometry and a K(d) of 1.2 microM. Taken together, our results demonstrate that FhuA is the receptor for MccJ25 and that the ligand-receptor interaction may occur in the absence of other components of the bacterial membrane. Finally, both differential scanning calorimetry and antimicrobial assays showed that MccJ25 binding involves external loops of FhuA. Unlike native MccJ25, a thermolysin-cleaved MccJ25 variant was unable to bind to FhuA and failed to prevent phage T5 infection of E. coli. Therefore the Val11-Pro16 beta-hairpin region of MccJ25, which is disrupted upon cleavage by thermolysin, is required for microcin recognition.
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Affiliation(s)
- Delphine Destoumieux-Garzón
- Chimie et Biochimie des Substances Naturelles, CNRS UMR 5154, Muséum National d'Histoire Naturelle USM 502, Département Régulations Développement et Diversité Moléculaire, 63 rue Buffon, 75005 Paris, France.
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28
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Annamalai R, Jin B, Cao Z, Newton SMC, Klebba PE. Recognition of ferric catecholates by FepA. J Bacteriol 2004; 186:3578-89. [PMID: 15150246 PMCID: PMC415739 DOI: 10.1128/jb.186.11.3578-3589.2004] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Escherichia coli FepA transports certain catecholate ferric siderophores, but not others, nor any noncatecholate compounds. Direct binding and competition experiments demonstrated that this selectivity originates during the adsorption stage. The synthetic tricatecholate Fe-TRENCAM bound to FepA with 50- to 100-fold-lower affinity than Fe-enterobactin (FeEnt), despite an identical metal center, and Fe-corynebactin only bound at much higher concentrations. Neither Fe-agrobactin nor ferrichrome bound at all, even at concentrations 10(6)-fold above the Kd. Thus, FepA only adsorbs catecholate iron complexes, and it selects FeEnt among even its close homologs. We used alanine scanning mutagenesis to study the contributions of surface aromatic residues to FeEnt recognition. Although not apparent from crystallography, aromatic residues in L3, L5, L7, L8, and L10 affected FepA's interaction with FeEnt. Among 10 substitutions that eliminated aromatic residues, Kd increased as much as 20-fold (Y481A and Y638A) and Km increased as much as 400-fold (Y478), showing the importance of aromaticity around the pore entrance. Although many mutations equally reduced binding and transport, others caused greater deficiencies in the latter. Y638A and Y478A increased Km 10- and 200-fold more, respectively, than Kd. N-domain loop deletions created the same phenotype: Delta60-67 (in NL1) and Delta98-105 (in NL2) increased Kd 10- to 20-fold but raised Km 500- to 700-fold. W101A (in NL2) had little effect on Kd but increased Km 1,000-fold. These data suggested that the primary role of the N terminus is in ligand uptake. Fluorescence and radioisotopic experiments showed biphasic release of FeEnt from FepA. In spectroscopic determinations, k(off1) was 0.03/s and k(off2) was 0.003/s. However, FepAY272AF329A did not manifest the rapid dissociation phase, corroborating the role of aromatic residues in the initial binding of FeEnt. Thus, the beta-barrel loops contain the principal ligand recognition determinants, and the N-domain loops perform a role in ligand transport.
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Affiliation(s)
- Rajasekaran Annamalai
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
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29
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Clément E, Mesini PJ, Pattus F, Schalk IJ. The Binding Mechanism of Pyoverdin with the Outer Membrane Receptor FpvA in Pseudomonas aeruginosa Is Dependent on Its Iron-Loaded Status. Biochemistry 2004; 43:7954-65. [PMID: 15196040 DOI: 10.1021/bi049768c] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In iron-deficient conditions, Pseudomonas aeruginosa secretes a major fluorescent siderophore named pyoverdin (Pvd), which after chelating iron(III) is transported back into the cell via its outer membrane receptor FpvA. FpvA is a TonB-dependent transport protein and has the ability to bind Pvd in its apo- or iron-loaded form. The fluorescence properties of Pvd were used to determine the binding kinetics of metal-free and metal-loaded Pvd to FpvA and showed two major features. First, the kinetics of formation of the FpvA-Pvd complex, in vivo and in vitro, are markedly slower compared to those observed for FpvA-Pvd-metal. Second, apo-Pvd and Pvd-metal absorbed with biphasic kinetics to FpvA: the bimolecular step (association of the ligand with the receptor) is followed by a slower step (t(1/2) values of 5 and 34 min for Pvd-metal and Pvd, respectively) that presumably leads to a more stable complex. The most likely explanation for this second step is that the binding of the ligand to the receptor induces a conformational change on FpvA, which may be different, depending on the loading status of Pvd. Analysis of the dissociation of metal-free Pvd from FpvA revealed an energy and a TonB dependency. The dissociation of iron-free Pvd from FpvA in the absence of the TonB protein occurs with slow kinetics in the range of hours, but it can be highly activated by the protonmotive force and TonB to reach a kinetic with a t(1/2) of 1 min. Apparently, under iron-limited conditions, TonB activates the FpvA receptor, resulting in a fast release of iron-free Pvd and generating an unloaded FpvA receptor, competent for binding extracellular Pvd-Fe.
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Affiliation(s)
- Emilie Clément
- Departement des Récepteurs et Protéines Membranaires, UPR 9050 CNRS, ESBS, Bld Sébastien Brandt, BP 10412, F-67413 Illkirch, Strasbourg, France
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30
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Cao Z, Warfel P, Newton SMC, Klebba PE. Spectroscopic observations of ferric enterobactin transport. J Biol Chem 2003; 278:1022-8. [PMID: 12409288 DOI: 10.1074/jbc.m210360200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We characterized the uptake of ferric enterobactin (FeEnt), the native Escherichia coli ferric siderophore, through its cognate outer membrane receptor protein, FepA, using a site-directed fluorescence methodology. The experiments first defined locations in FepA that were accessible to covalent modification with fluorescein maleimide (FM) in vivo; among 10 sites that we tested by substituting single Cys residues, FM labeled W101C, S271C, F329C, and S397C, and all these exist within surface-exposed loops of the outer membrane protein. FeEnt normally adsorbed to the fluoresceinated S271C and S397C mutant FepA proteins in vivo, which we observed as quenching of fluorescence intensity, but the ferric siderophore did not bind to the FM-modified derivatives of W101C or F329C. These in vivo fluorescence determinations showed, for the first time, consistency with radioisotopic measurements of the affinity of the FeEnt-FepA interaction; K(d) was 0.2 nm by both methods. Analysis of the FepA mutants with AlexaFluor(680), a fluorescein derivative with red-shifted absorption and emission spectra that do not overlap the absorbance spectrum of FeEnt, refuted the possibility that the fluorescence quenching resulted from resonance energy transfer. These and other data instead indicated that the quenching originated from changes in the environment of the fluor as a result of loop conformational changes during ligand binding and transport. We used the fluorescence system to monitor FeEnt uptake by live bacteria and determined its dependence on ligand concentration, temperature, pH, and carbon sources and its susceptibility to inhibition by the metabolic poisons. Unlike cyanocobalamin transport through the outer membrane, FeEnt uptake was sensitive to inhibitors of electron transport and phosphorylation, in addition to its sensitivity to proton motive force depletion.
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Affiliation(s)
- Zhenghua Cao
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman 73019, USA
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31
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Folschweiller N, Gallay J, Vincent M, Abdallah MA, Pattus F, Schalk IJ. The interaction between pyoverdin and its outer membrane receptor in Pseudomonas aeruginosa leads to different conformers: a time-resolved fluorescence study. Biochemistry 2002; 41:14591-601. [PMID: 12463759 DOI: 10.1021/bi0259711] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In iron limitation conditions, Pseudomonas aeruginosa secretes a major fluorescent siderophore named pyoverdin (PaA). PaA has an extremely high affinity for Fe(3+) but also chelates other ions such as Al(3+) and Ga(3+) with a lower affinity. The transfer of PaA-Fe(3+) across the outer membrane of the bacteria is mediated by the receptor FpvA, a TonB-dependent outer membrane transport protein. FpvA binds the iron-free and iron-loaded forms of pyoverdin with similar affinities, but only PaA-Fe(3+) is taken up by the cell, suggesting that FpvA adopts different conformations depending on its loading status. We used time-resolved fluorescence spectroscopy to characterize the different forms of FpvA-PaA in vitro. We showed that the FpvA-PaA complex adopts two different conformations depending on how it was prepared (formed in vitro or in vivo prior to purification). The dihydroquinoline moiety of both conformers is fully protonated, or coordinated by protein charged groups, but the polarity of its environment, its solvent accessibility, and its rotational dynamics are much slower when the FpvA-PaA complex is formed in vivo than in vitro. In the presence of Ga(3+) or Al(3+) ions, the solvent accessibility and mobility of the dihydroquinoline moiety in the two FpvA-PaA complexes are intermediate between those observed for the metal-free ones. In addition, the Förster resonance energy transfer kinetics from FpvA tryptophan residues to the PaA chromophore differs from one complex to the other, revealing differences in one or more of the donor-acceptor topologies.
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Affiliation(s)
- Nicolas Folschweiller
- ESBS, Ecole Supérieure de Biotechnologie de Strasbourg, UPR CNRS 9050, Bld Sébastien Brant, 67400 Illkirch, France
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32
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Abstract
Bacteria solve the iron supply problem caused by the insolubility of Fe(3+) by synthesizing iron-complexing compounds, called siderophores, and by using iron sources of their hosts, such as heme and iron bound to transferrin and lactoferrin. Escherichia coli, as an example of Gram-negative bacteria, forms sophisticated Fe(3+)-siderophore and heme transport systems across the outer membrane. The crystal structures of three outer membrane transport proteins now allow insights into energy-coupled transport mechanisms. These involve large long-range structural transitions in the transport proteins in response to substrate binding, including substrate gating. Energy is provided by the proton motive force of the cytoplasmic membrane through the activity of a protein complex that is inserted in the cytoplasmic membrane and that contacts the outer membrane transporters. Certain transport proteins also function in siderophore-mediated signaling cascades that start at the cell surface and flow to the cytoplasm to initiate transcription of genes encoding proteins for transport and siderophore biosynthesis.
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Affiliation(s)
- Volkmar Braun
- Microbiology/Membranephysiology, University of Tübingen, Auf der Morgenstelle 28, D-72076, Tübingen, Germany.
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33
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Abstract
Using a lysine-specific cleavable cross-linking reagent ethylene glycolbis(sulfosuccimidylsuccinate) (Sulfo-EGS), we studied conformational motion in the surface loops of Escherichia coli FepA during its transport of the siderophore ferric enterobactin. Site-directed mutagenesis determined that Sulfo-EGS reacted with two lysines, K332 and K483, and at least two other unidentified Lys residues in the surface loops of the outer membrane protein. The reagent cross-linked K483 in FepA L7 to either K332 in L5, forming a product that we designated band 1, or to the major outer membrane proteins OmpF, OmpC, and OmpA, forming band 2. Ferric enterobactin binding to FepA did not prevent modification of K483 by Sulfo-EGS but blocked its cross-linking to OmpF/C and OmpA and reduced its coupling to K332. These data show that the loops of FepA undergo conformational changes in vivo, with an approximate magnitude of 15 A, from a ligand-free open state to a ligand-bound closed state. The coupling of FepA L7 to OmpF, OmpC, or OmpA was TonB independent and was unaffected by the uncouplers CCCP (carbonyl cyanide m-chlorophenylhydrazone) and DNP (2,4-dinitrophenol) but completely inhibited by cyanide.
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Affiliation(s)
- Daniel C Scott
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
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de Zamaroczy M, Buckingham RH. Importation of nuclease colicins into E coli cells: endoproteolytic cleavage and its prevention by the immunity protein. Biochimie 2002; 84:423-32. [PMID: 12423785 DOI: 10.1016/s0300-9084(02)01426-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A major group of colicins comprises molecules that possess nuclease activity and kill sensitive cells by cleaving RNA or DNA. Recent data open the possibility that the tRNase colicin D, the rRNase colicin E3 and the DNase colicin E7 undergo proteolytic processing, such that only the C-terminal domain of the molecule, carrying the nuclease activity, enters the cytoplasm. The proteases responsible for the proteolytic processing remain unidentified. In the case of colicin D, the characterization of a colicin D-resistant mutant shows that the inner membrane protease LepB is involved in colicin D toxicity, but is not solely responsible for the cleavage of colicin D. The lepB mutant resistant to colicin D remains sensitive to other colicins tested (B, E1, E3 and E2), and the mutant protease retains activity towards its normal substrates. The cleavage of colicin D observed in vitro releases a C-terminal fragment retaining tRNase activity, and occurs in a region of the amino acid sequence that is conserved in other nuclease colicins, suggesting that they may also require a processing step for their cytotoxicity. The immunity proteins of both colicins D and E3 appear to have a dual role, protecting the colicin molecule against proteolytic cleavage and inhibiting the nuclease activity of the colicin. The possibility that processing is an essential step common to cell killing by all nuclease colicins, and that the immunity protein must be removed from the colicin prior to processing, is discussed.
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Affiliation(s)
- Miklos de Zamaroczy
- Institut de Biologie Physico-Chimique, CNRS, UPR 9073, 13, rue Pierre et Marie Curie 75005, Paris, France.
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35
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Abstract
To kill Escherichia coli, toxic proteins, called colicins, pass through the permeability barrier created by the outer membrane (OM) of the bacterial cell envelope. We consider a variety of different colicins, including A, B, D, E1, E3, Ia, M and N, that penetrate through the porins OmpF, FepA, BtuB, Cir and FhuA, to subsequently interact with a few targets in the periplasm, including TolA, TolB, TolC and TonB. We review the mechanisms, demonstrated and postulated, by which such toxins enter bacterial cells, from the initial binding stage on the cell surface to the internalization reaction through the OM bilayer. Our discussions endeavor to answer two main questions: what is the origin of colicin-binding affinity and specificity, and after adsorption to OM porins, do colicin polypeptides translocate through porin channels, or enter by another, currently unknown pathway?
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Affiliation(s)
- Zhenghua Cao
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA
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36
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Starr TE, Thompson NL. Local Diffusion and Concentration of IgG near Planar Membranes: Measurement by Total Internal Reflection with Fluorescence Correlation Spectroscopy. J Phys Chem B 2002. [DOI: 10.1021/jp012689f] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Tammy E. Starr
- Department of Chemistry, Campus Box 3290, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290
| | - Nancy L. Thompson
- Department of Chemistry, Campus Box 3290, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290
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37
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de Zamaroczy M, Mora L, Lecuyer A, Géli V, Buckingham RH. Cleavage of colicin D is necessary for cell killing and requires the inner membrane peptidase LepB. Mol Cell 2001; 8:159-68. [PMID: 11511369 DOI: 10.1016/s1097-2765(01)00276-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Colicin D is known to kill target cells by cleaving tRNA(Arg). A colicin D-resistant mutant was selected that was altered in the inner membrane leader peptidase, LepB. The substituted residue (Asn274Lys) is located close to the catalytic site. The mutation abolishes colicin D cleavage but not the processing of exported proteins. LepB is required for colicin D cleavage, releasing a small C-terminal fragment that retains full tRNase activity. The immunity protein was found to prevent colicin D processing and furthermore masks tRNase activity, thus protecting colicin D against LepB-mediated cleavage during export. Catalytic colicins share a consensus sequence at their putative processing site. Mutations affecting normal processing of colicin D abolish cytotoxicity without affecting the in vitro tRNase activity.
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Affiliation(s)
- M de Zamaroczy
- Institut de Biologie Physico-Chimique, CNRS, UPR 9073, 75005, Paris, France.
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38
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Scott DC, Cao Z, Qi Z, Bauler M, Igo JD, Newton SM, Klebba PE. Exchangeability of N termini in the ligand-gated porins of Escherichia coli. J Biol Chem 2001; 276:13025-33. [PMID: 11278876 DOI: 10.1074/jbc.m011282200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ferric siderophore transporters of the Gram-negative bacterial outer membrane manifest a unique architecture: Their N termini fold into a globular domain that lodges within, and physically obstructs, a transmembrane porin beta-barrel formed by their C termini. We exchanged and deleted the N termini of two such siderophore receptors, FepA and FhuA, which recognize and transport ferric enterobactin and ferrichrome, respectively. The resultant chimeric proteins and empty beta-barrels avidly bound appropriate ligands, including iron complexes, protein toxins, and viruses. Thus, the ability to recognize and discriminate these molecules fully originates in the transmembrane beta-barrel domain. Both the hybrid and the deletion proteins also transported the ferric siderophore that they bound. The FepA constructs showed less transport activity than wild type receptor protein, but the FhuA constructs functioned with turnover numbers that were equivalent to wild type. The mutant proteins displayed the full range of transport functionalities, despite their aberrant or missing N termini, confirming (Braun, M., Killmann, H., and Braun, V. (1999) Mol. Microbiol. 33, 1037-1049) that the globular domain within the pore is dispensable to the siderophore internalization reaction, and when present, acts without specificity during solute uptake. These and other data suggest a transport process in which siderophore receptors undergo multiple conformational states that ultimately expel the N terminus from the channel concomitant with solute internalization.
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Affiliation(s)
- D C Scott
- Department of Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
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39
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Cao Z, Qi Z, Sprencel C, Newton SM, Klebba PE. Aromatic components of two ferric enterobactin binding sites in Escherichia coli FepA. Mol Microbiol 2000; 37:1306-17. [PMID: 10998164 DOI: 10.1046/j.1365-2958.2000.02093.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ferric enterobactin is a catecholate siderophore that binds with high affinity (Kd approximately 10-10 M) to the Escherichia coli outer membrane protein FepA. We studied the involvement of aromatic amino acids in its uptake by determining the binding affinities, kinetics and transport properties of site-directed mutants. We replaced seven aromatic residues (Y260, Y272, Y285, Y289, W297, Y309 and F329) in the central part of FepA primary structure with alanine, individually and in double combinations, and determined the ability of the mutant proteins to interact with ferric enterobactin and the protein toxins colicins B and D. All the constructs showed normal expression and localization. Among single mutants, Y260A and F329A were most detrimental, reducing the affinity between FepA and ferric enterobactin 100- and 10-fold respectively. Double substitutions involving Y260, Y272 and F329 impaired (100- to 2500-fold) adsorption of the iron chelate more strongly. For Y260A and Y272A, the drop in adsorption affinity caused commensurate decreases in transport efficiency, suggesting that the target residues primarily act in ligand binding. F329A, like R316A, showed greater impairment of transport than binding, intimating mechanistic involvement during ligand internalization. Furthermore, immunochemical studies localized F329 in the FepA ligand binding site. The mutagenesis results suggested the existence of dual ligand binding sites in the FepA vestibule, and measurements of the rate of ferric enterobactin adsorption to fluoresceinated FepA mutant proteins confirmed this conclusion. The initial, outermost site contains aromatic residues and probably functions through hydrophobic interactions, whereas the secondary site exists deeper in the vestibule, contains both charged and aromatic residues and probably acts through hydrophobic and electrostatic bonds.
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Affiliation(s)
- Z Cao
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
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40
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Schalk IJ, Kyslik P, Prome D, van Dorsselaer A, Poole K, Abdallah MA, Pattus F. Copurification of the FpvA ferric pyoverdin receptor of Pseudomonas aeruginosa with its iron-free ligand: implications for siderophore-mediated iron transport. Biochemistry 1999; 38:9357-65. [PMID: 10413510 DOI: 10.1021/bi990421x] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Pseudomonas aeruginosa FpvA receptor is a TonB-dependent outer membrane transport protein that catalyzes uptake of ferric pyoverdin across the outer membrane. Surprisingly, FpvA expressed in P. aeruginosa grown in an iron-deficient medium copurifies with a ligand X that we have characterized by UV, fluorescence, and mass spectrometry as being iron-free pyoverdin (apo-PaA). PaA was absent from FpvA purified from a PaA-deficient P. aeruginosa strain. The properties of ligand binding in vitro revealed very similar affinities of apo-PaA and ferric-PaA to FpvA. Fluorescence resonance energy transfer was used to study in vitro the formation of the FpvA-PaA-Fe complex in the presence of PaA-Fe or citrate-Fe. The circular dichroism spectrum of FpvA indicated a 57% beta-structure content typical of porins and in agreement with the 3D structures of the siderophore receptors FhuA and FepA. In the absence of the protease's inhibitors, a truncated form of FpvA lacking 87 amino acids at its N-terminus was purified. This truncated form still bound PaA, and its beta-sheet content was conserved. This N-terminal region displays significant homology to the N-terminal periplasmic extensions of FecA from Escherichia coli and PupB from Pseudomonas putida, which were previously shown to be involved in signal transduction. This suggests a similar function for FpvA. The mechanism of iron transport in P. aeruginosa via the pyoverdin pathway is discussed in the light of all these new findings.
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Affiliation(s)
- I J Schalk
- Département des Récepteurs et Protéines Membranaires, UPR 9050 CNRS, ESBS, Strasbourg, France.
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41
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Newton SM, Igo JD, Scott DC, Klebba PE. Effect of loop deletions on the binding and transport of ferric enterobactin by FepA. Mol Microbiol 1999; 32:1153-65. [PMID: 10383757 DOI: 10.1046/j.1365-2958.1999.01424.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The siderophore ferric enterobactin enters Escherichia coli through the outer membrane (OM) porin FepA, which contains an aqueous transmembrane channel that is normally occluded by other parts of the protein. After binding the siderophore at a site within the surface loops, FepA undergoes conformational changes that promote ligand internalization. We assessed the participation of different loops in ligand recognition and uptake by creating and analysing a series of deletions. We genetically engineered 26 mutations that removed 9-75 amino acids from nine loops and two buried regions of the OM protein. The mutations had various effects on the uptake reaction, which we discerned by comparing the substrate concentrations of half-maximal binding (Kd) and uptake (Km): every loop deletion affected siderophore transport kinetics, decreasing or eliminating binding affinity and transport efficiency. We classified the mutations in three groups on the basis of their slight, strong or complete inhibition of the rate of ferric enterobactin transport across the OM. Finally, characterization of the FepA mutants revealed that prior experiments underestimated the affinity of FepA for ferric enterobactin: the interaction between the protein and the ferric siderophore is so avid (Kd < 0.2 nM) that FepA tolerated the large reductions in affinity that some loop deletions caused without loss of uptake functionality. That is, like other porins, many of the loops of FepA are superficially dispensable: ferric enterobactin transport occurred without them, at levels that allowed bacterial growth.
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Affiliation(s)
- S M Newton
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA
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Thulasiraman P, Newton SM, Xu J, Raymond KN, Mai C, Hall A, Montague MA, Klebba PE. Selectivity of ferric enterobactin binding and cooperativity of transport in gram-negative bacteria. J Bacteriol 1998; 180:6689-96. [PMID: 9852016 PMCID: PMC107775 DOI: 10.1128/jb.180.24.6689-6696.1998] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ligand-gated outer membrane porin FepA serves Escherichia coli as the receptor for the siderophore ferric enterobactin. We characterized the ability of seven analogs of enterobactin to supply iron via FepA by quantitatively measuring the binding and transport of their 59Fe complexes. The experiments refuted the idea that chirality of the iron complex affects its recognition by FepA and demonstrated the necessity of an unsubstituted catecholate coordination center for binding to the outer membrane protein. Among the compounds we tested, only ferric enantioenterobactin, the synthetic, left-handed isomer of natural enterobactin, and ferric TRENCAM, which substitutes a tertiary amine for the macrocyclic lactone ring of ferric enterobactin but maintains an unsubstituted catecholate iron complex, were recognized by FepA (Kd approximately 20 nM). Ferric complexes of other analogs (TRENCAM-3,2-HOPO; TREN-Me-3,2-HOPO; MeMEEtTAM; MeME-Me-3,2-HOPO; K3MECAMS; agrobactin A) with alterations to the chelating groups and different net charge on the iron center neither adsorbed to nor transported through FepA. We also compared the binding and uptake of ferric enterobactin by homologs of FepA from Bordetella bronchisepticus, Pseudomonas aeruginosa, and Salmonella typhimurium in the native organisms and as plasmid-mediated clones expressed in E. coli. All the transport proteins bound ferric enterobactin with high affinity (Kd </= 100 nM) and transported it at comparable rates (>/=50 pmol/min/10(9) cells) in their own particular membrane environments. However, the FepA and IroN proteins of S. typhimurium failed to efficiently function in E. coli. For E. coli, S. typhimurium, and P. aeruginosa, the rate of ferric enterobactin uptake was a sigmoidal function of its concentration, indicating a cooperative transport reaction involving multiple interacting binding sites on FepA.
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Affiliation(s)
- P Thulasiraman
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
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Klebba PE, Newton SM. Mechanisms of solute transport through outer membrane porins: burning down the house. Curr Opin Microbiol 1998; 1:238-47. [PMID: 10066479 DOI: 10.1016/s1369-5274(98)80017-9] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Porins mediate the uptake of nutrients across the outer membrane of Gram-negative bacteria. For general porins like OmpF, electrophysicoloigcal experiments now establish that the charged residues within their channels primarily modulate pore selectivity, rather than voltage-gated switching between open and closed states. Recent studies on the maltoporin, LamB, solidify the importance of its 'greasy slide' aromatic residues during sugar transport, and suggest the involvement of L9, in the exterior vestibule, as the initial maltodextrin binding site. The application of biophysical methodologies to the TonB-dependent porin, FepA, ostensibly reveal the opening and closing of its channel during ligand uptake, a phenomenon that was predicted but not previously demonstrated.
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Affiliation(s)
- P E Klebba
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019, USA
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