Evidence of Ball-and-chain Transport of Ferric Enterobactin through FepA
Open accessAbstract
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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When expressing an LGP of interest, OKN3 and OKN359 (both tonB+) were capable of ferric catecholate binding and transport; OKN13 (ΔtonB) bound but could not transport iron complexes.
“When expressing an LGP of interest, OKN3 and OKN359 (both tonB + ) were capable of ferric catecholate binding and transport; OKN13 (ΔtonB), on the other hand, bound but could not transport iron complexes.”
From Siderophore-mediated iron acquisition by <i>Klebsiella pneumoniae</i> (2024) · cites this paper as [23]
The Results (page unavailable) report that OKN3 expressing FepA bound and transported ferric enterobactin. The Cellular Distribution section (page unavailable) says TonB-deficient cells bind but do not transport it, consistent with the claim about OKN13. The Results identify OKN359 as a constructed deletion strain but do not report its binding or transport when expressing a receptor; the paper also does not establish this behavior for any LGP of interest. (LLM, conf=0.86)
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Cites
Experiments in molecular genetics
Miller, J. H. (1972) · Medical Entomology and Zoology · Cited by 27,157 · see citing works
One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products.
Datsenko, K., & Wanner, B. (2000) · Proceedings of the National Academy of Sciences of the United States of America · doi:10.1073/pnas.120163297 · Cited by 15,902 · see citing works
Molecular Basis of Bacterial Outer Membrane Permeability Revisited
Nikaido, H. (2003) · Microbiology and Molecular Biology Reviews · doi:10.1128/mmbr.67.4.593-656.2003 · Cited by 4,316 · see citing works
Culture Medium for Enterobacteria
Neidhardt, F. C., Bloch, P. L., & Smith, D. F. (1974) · Journal of Bacteriology · doi:10.1128/jb.119.3.736-747.1974 · Cited by 2,977 · see citing works
Inactivation of the sodium channel. II. Gating current experiments.
Armstrong, C. M., & Bezanilla, F. (1977) · The Journal of General Physiology · doi:10.1085/jgp.70.5.567 · Cited by 953 · see citing works
Siderophore-Mediated Iron Transport: Crystal Structure of FhuA with Bound Lipopolysaccharide
Ferguson, A. D., Hofmann, E., Coulton, J. W., Diederichs, K., & Welte, W. (1998) · Science · doi:10.1126/science.282.5397.2215 · Cited by 787 · see citing works
Resolution of Bacterial Proteins by Polyacrylamide Gel Electrophoresis on Slabs
Ames, G. F. (1974) · Journal of Biological Chemistry · doi:10.1016/s0021-9258(19)43074-3 · Cited by 753 · see citing works
Crystal structure of the outer membrane active transporter FepA from Escherichia coli.
Buchanan (1999) · Nature Structural Biology · doi:10.1038/4931 · Cited by 591 · see citing works
Molecular basis of bacterial outer membrane permeability
Nikaido, H., & Vaara, M. (1985) · Microbiological Reviews · doi:10.1128/mr.49.1.1-32.1985 · Cited by 553 · see citing works
Transmembrane Signaling across the Ligand-Gated FhuA Receptor
Locher, K. P., Rees, B., Koebnik, R., Mitschler, A., Moulinier, L., Rosenbusch, J. P., & Moras, D. (1998) · Cell · doi:10.1016/s0092-8674(00)81700-6 · Cited by 540 · see citing works
Porin channels in Escherichia coli: studies with liposomes reconstituted from purified proteins
Nikaido, H., & Rosenberg, E. Y. (1983) · Journal of Bacteriology · doi:10.1128/jb.153.1.241-252.1983 · Cited by 448 · see citing works
Porin channels in Escherichia coli: studies with beta-lactams in intact cells
Nikaido, H., Rosenberg, E., & Foulds, J. (1983) · Journal of Bacteriology · doi:10.1128/jb.153.1.232-240.1983 · Cited by 395 · see citing works
Smit, J., Kamio, Y., & Nikaido, H. (1975) · Journal of Bacteriology · doi:10.1128/jb.124.2.942-958.1975 · Cited by 362 · see citing works
Outer Membrane Active Transport: Structure of the BtuB:TonB Complex
Shultis, D., Purdy, M. D., Banchs, C. N., & Wiener, M. C. (2006) · Science · doi:10.1126/science.1127694 · Cited by 303 · see citing works
Substrate-induced transmembrane signaling in the cobalamin transporter BtuB
Chimento, D. P., Mohanty, A. K., Kadner, R. J., & Wiener, M. C. (2003) · Nature Structural & Molecular Biology · doi:10.1038/nsb914 · Cited by 289 · see citing works
Structure of TonB in Complex with FhuA, E. coli Outer Membrane Receptor
Pawelek, P. D., Croteau, N., Ng‐Thow‐Hing, C., Khursigara, C. M., Moiseeva, N., Allaire, M., & Coulton, J. W. (2006) · Science · doi:10.1126/science.1128057 · Cited by 273 · see citing works
Masi, D. R. D., White, J. C., Schnaitman, C. A., & Bradbeer, C. (1973) · Journal of Bacteriology · doi:10.1128/jb.115.2.506-513.1973 · Cited by 263 · see citing works
Pore-forming activity of OmpA protein of Escherichia coli.
Sugawara, E., & Nikaido, H. (1992) · Journal of Biological Chemistry · doi:10.1016/s0021-9258(18)45908-x · Cited by 253 · see citing works
TonB protein and energy transduction between membranes
Postle, K. (1993) · Journal of Bioenergetics and Biomembranes · doi:10.1007/bf00770246 · Cited by 217 · see citing works
The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli
Bradbeer, C. (1993) · Journal of Bacteriology · doi:10.1128/jb.175.10.3146-3150.1993 · Cited by 188 · see citing works
Cobessi, D., Celia, H., Folschweiller, N., Schalk, I. J., Abdallah, M. A., & Pattus, F. (2005) · Journal of Molecular Biology · doi:10.1016/j.jmb.2005.01.021 · Cited by 188 · see citing works
Hashimoto-Gotoh, T., Franklin, F. C. H., Nordheim, A., & Timmis, K. N. (1981) · Gene · doi:10.1016/0378-1119(81)90079-2 · Cited by 188 · see citing works
Iron Uptake in Salmonella typhimurium : Utilization of Exogenous Siderochromes as Iron Carriers
Luckey, M., Pollack, J. R., Wayne, R. R., Ames, B. N., & Neilands, J. B. (1972) · Journal of Bacteriology · doi:10.1128/jb.111.3.731-738.1972 · Cited by 186 · see citing works
Formation of a Gated Channel by a Ligand-Specific Transport Protein in the Bacterial Outer Membrane
Rutz, J. M., Liu, J., Lyons, J. A., Goranson, J., Armstrong, S. K., McIntosh, M. A., Feix, J. B., & Klebba, P. E. (1992) · Science · doi:10.1126/science.1411544 · Cited by 165 · see citing works
Self-citationReynolds, P. R., Mottur, G. P., & Bradbeer, C. (1980) · Journal of Biological Chemistry · doi:10.1016/s0021-9258(19)85667-3 · Cited by 142 · see citing works
Siderophore protection against colicins M, B, V, and Ia in Escherichia coli
Wayne, R. R., Frick, K., & Neilands, J. B. (1976) · Journal of Bacteriology · doi:10.1128/jb.126.1.7-12.1976 · Cited by 125 · see citing works
Surface topology of the Escherichia coli K-12 ferric enterobactin receptor
Murphy, C. K., Kalve, V. I., & Klebba, P. E. (1990) · Journal of Bacteriology · doi:10.1128/jb.172.5.2736-2746.1990 · Cited by 115 · see citing works
Self-citationKinetics of Biosynthesis of Iron-Regulated Membrane Proteins in Escherichia coli
Klebba, P. E., McIntosh, M. A., & Neilands, J. B. (1982) · Journal of Bacteriology · doi:10.1128/jb.149.3.880-888.1982 · Cited by 108 · see citing works
Self-citationBradbeer, C., Woodrow, M. L., & Khalifah, L. I. (1976) · Journal of Bacteriology · doi:10.1128/jb.125.3.1032-1039.1976 · Cited by 104 · see citing works
Substrate-induced exposure of an energy-coupling motif of a membrane transporter.
Kadner, R. J., Cafiso, D. S., Merianos, H. J., Cadieux, N., & Lin, C. H. (2000) · Nature Structural Biology · doi:10.1038/73309 · Cited by 95 · see citing works
Iron uptake in colicin B-resistant mutants of Escherichia coli K-12
Pugsley, A. P., & Reeves, P. R. (1976) · Journal of Bacteriology · doi:10.1128/jb.126.3.1052-1062.1976 · Cited by 94 · see citing works
An Additional Step in the Transport of Iron Defined by the tonB Locus of Escherichia coli
Wang, C. C., & Newton, A. (1971) · Journal of Biological Chemistry · doi:10.1016/s0021-9258(19)77201-9 · Cited by 93 · see citing works
Evolution of the ferric enterobactin receptor in gram-negative bacteria
Rutz, J. M., Abdullah, T., SINGH, S. P., Kalve, V. I., & Klebba, P. E. (1991) · Journal of Bacteriology · doi:10.1128/jb.173.19.5964-5974.1991 · Cited by 92 · see citing works
Self-citationLigand-Specific Opening of a Gated-Porin Channel in the Outer Membrane of Living Bacteria
Jiang, X., Payne, M. A., Cao, Z., Foster, S. B., Feix, J. B., Newton, S. M. C., & Klebba, P. E. (1997) · Science · doi:10.1126/science.276.5316.1261 · Cited by 92 · see citing works
Self-citationEffect of loop deletions on the binding and transport of ferric enterobactin by FepA
Newton, S. M. C., Igo, J. D., Scott, D. C., & Klebba, P. E. (1999) · Molecular Microbiology · doi:10.1046/j.1365-2958.1999.01424.x · Cited by 91 · see citing works
Self-citationExcretion of Enterochelin by exbA and exbB Mutants of Escherichia coli
Guterman, S. K., & Dann, L. (1973) · Journal of Bacteriology · doi:10.1128/jb.114.3.1225-1230.1973 · Cited by 89 · see citing works
Families of Proteins Forming Transmembrane Channels
M.H. Saier (2000) · The Journal of Membrane Biology · doi:10.1007/s00232001065 · Cited by 82 · see citing works
Binding of Ferric Enterobactin by theEscherichia coliPeriplasmic Protein FepB
Sprencel, C., Cao, Z., Qi, Z., Scott, D. C., Montague, M. A., Ivanoff, N., Xu, J., Raymond, K., Newton, S. M. C., & Klebba, P. E. (2000) · Journal of Bacteriology · doi:10.1128/jb.182.19.5359-5364.2000 · Cited by 82 · see citing works
Self-citationIron Transport in Escherichia coli: Roles of Energy-dependent Uptake and 2,3-Dihydroxybenzoylserine
Wang, C. C., & Newton, A. (1969) · Journal of Bacteriology · doi:10.1128/jb.98.3.1142-1150.1969 · Cited by 80 · see citing works
Recognition of Ferric Catecholates by FepA
Annamalai, R., Jin, B., Cao, Z., Newton, S. M. C., & Klebba, P. E. (2004) · Journal of Bacteriology · doi:10.1128/jb.186.11.3578-3589.2004 · Cited by 73 · see citing works
Self-citationFamilies of Proteins Forming Transmembrane Channels
Saier, M. H. (2000) · The Journal of Membrane Biology · doi:10.1007/s002320001065 · Cited by 72 · see citing works
Braun, V., & Wolff, H. (1973) · FEBS Letters · doi:10.1016/0014-5793(73)80707-0 · Cited by 69 · see citing works
Usher, K. C., Özkan, E., Gardner, K. H., & Deisenhofer, J. (2001) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.181353398 · Cited by 67 · see citing works
Exchangeability of N Termini in the Ligand-gated Porins ofEscherichia coli
Scott, D. C., Cao, Z., Qi, Z., Bauler, M. N., Igo, J. D., Newton, S. M. C., & Klebba, P. E. (2001) · Journal of Biological Chemistry · doi:10.1074/jbc.m011282200 · Cited by 64 · see citing works
Self-citationEisenhauer, H. A., Shames, S., Pawelek, P. D., & Coulton, J. W. (2005) · Journal of Biological Chemistry · doi:10.1074/jbc.m506708200 · Cited by 59 · see citing works
Biphasic Binding Kinetics between FepA and Its Ligands
Payne, M. A., Igo, J. D., Cao, Z., Foster, S. B., Newton, S. M. C., & Klebba, P. E. (1997) · Journal of Biological Chemistry · doi:10.1074/jbc.272.35.21950 · Cited by 59 · see citing works
Self-citationThree paradoxes of ferric enterobactin uptake
Klebba, P. E. (2003) · Frontiers in bioscience · doi:10.2741/1233 · Cited by 56 · see citing works
Self-citationMcIntosh, M. A., & Earhart, C. F. (1976) · Biochemical and Biophysical Research Communications · doi:10.1016/0006-291x(76)91144-x · Cited by 53 · see citing works
Newton, S. M. C., Allen, J. S., Cao, Z., Qi, Z., Jiang, X., Sprencel, C., Igo, J. D., Foster, S. B., Payne, M. A., & Klebba, P. E. (1997) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.94.9.4560 · Cited by 53 · see citing works
Self-citationUptake of ferrienterochelin by Escherichia coli: energy dependent stage of uptake
Pugsley, A. P., & Reeves, P. R. (1977) · Journal of Bacteriology · doi:10.1128/jb.130.1.26-36.1977 · Cited by 50 · see citing works
Bradbeer, C., Kenley, J. S., Masi, D. R. D., & Leighton, M. (1978) · Journal of Biological Chemistry · doi:10.1016/s0021-9258(17)34873-1 · Cited by 48 · see citing works
In Vivo Reconstitution of the FhuA Transport Protein ofEscherichia coliK-12
Braun, M., Endriß, F., Killmann, H., & Braun, V. (2003) · Journal of Bacteriology · doi:10.1128/jb.185.18.5508-5518.2003 · Cited by 47 · see citing works
Aromatic components of two ferric enterobactin binding sites in <i>Escherichia coli</i> FepA
Cao, Z., Qi, Z., Sprencel, C., Newton, S. M. C., & Klebba, P. E. (2000) · Molecular Microbiology · doi:10.1046/j.1365-2958.2000.02093.x · Cited by 45 · see citing works
Self-citationDifferential substrate-induced signaling through the TonB-dependent transporter BtuB
Cadieux, N., Phan, P. G., Cafiso, D. S., & Kadner, R. J. (2003) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.1932538100 · Cited by 43 · see citing works
Spectroscopic Observations of Ferric Enterobactin Transport
Cao, Z., Warfel, P., Newton, S. M. C., & Klebba, P. E. (2003) · Journal of Biological Chemistry · doi:10.1074/jbc.m210360200 · Cited by 39 · see citing works
Self-citationScott, D. C., Newton, S. M. C., & Klebba, P. E. (2002) · Journal of Bacteriology · doi:10.1128/jb.184.17.4906-4911.2002 · Cited by 35 · see citing works
Self-citationFepA with Globular Domain Deletions Lacks Activity
Vakharia, H., & Postle, K. (2002) · Journal of Bacteriology · doi:10.1128/jb.184.19.5508-5512.2002 · Cited by 34 · see citing works
Luckey, M., & Neilands, J. B. (1976) · Journal of Bacteriology · doi:10.1128/jb.127.2.1036-1037.1976 · Cited by 20 · see citing works
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- Newton, S. M., Allen, J. S., Cao, Z., Qi, Z., Jiang, X., Sprencel, C., Igo, J. D., Foster, S. B., Payne, M. A., and Klebba, P. E. (1997) Proc. Natl. Acad. Sci.
- Usher, K. C., Ozkan, E., Gardner, K. H., and Deisenhofer, J. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 10676 -10681
- Datsenko, K. A., and Wanner, B. L. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 6640 -6645
- Cadieux, N., Phan, P. G., Cafiso, D. S., and Kadner, R. J. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 10688 -10693
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Noinaj, N., Guillier, M., Barnard, & Buchanan, S. K. (2010) · Annual Review of Microbiology · doi:10.1146/annurev.micro.112408.134247 · Cited by 989 · see citing works
New substrates for TonB-dependent transport: do we only see the ‘tip of the iceberg’?
Schauer, K., Rodionov, D. A., & de Reuse, H. (2008) · Trends in Biochemical Sciences · doi:10.1016/j.tibs.2008.04.012 · Cited by 360 · see citing works
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Klebba, P. E. (2016) · Journal of Bacteriology · doi:10.1128/jb.00823-15 · Cited by 52 · see citing works
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“The structural features of LGP raised the possibility of ligand transport by a “Ball and Chain” mechanism (Armstrong and Bezanilla, 1977), in which the N-terminus dislodges from the channel into the periplasm (Ma et al., 2007).”
BackgroundMethodInfluentialSelf-citationUniversal fluorescent sensors of high-affinity iron transport, applied to ESKAPE pathogens
Chakravorty, S., Shipelskiy, Y., Kumar, A., Majumdar, A., Yang, T., Nairn, B. L., Newton, S. M., & Klebba, P. E. (2019) · Journal of Biological Chemistry · doi:10.1074/jbc.ra118.006921 · Cited by 11 · see citing works
Self-citation
- Authors
- Ma, L., Kaserer, W., Annamalai, R., Scott, D. C., Jin, B., Jiang, X., Xiao, Q., Maymani, H., Massis, L. M., Ferreira, L. C. S., Newton, S. M. C., & Klebba, P. E.
- Affiliations
- University of Oklahoma (US)
- Universidade de São Paulo (BR)
- Corresponding author
- Klebba, Phillip E.
- ORCID
- Venue
- Journal of Biological Chemistry
- Publisher
- Elsevier BV
- Published
- 2007-01
- Volume
- 282
- Issue
- 1
- Pages
- 397-406
- ISSN
- 0021-9258 (ISSN-L)
- PMC
- PMC2398697
- OpenAlex
- W2121209974
- Cited by
- 84
- References
- 58
- Citations by year
- 2026: 2 · 2025: 1 · 2024: 3 · 2023: 2 · 2022: 2 · 2021: 4 · 2020: 6 · 2019: 1 · 2018: 1 · 2017: 2 · 2016: 6 · 2015: 3 · 2014: 4 · 2013: 3 · 2012: 7
- FWCI
- 4.35
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- Journal of Biological Chemistry (publishedVersion, cc-by)
- PubMed (publishedVersion)
- PubMed Central (acceptedVersion)
- Funders
- National Science Foundation
- Fundação de Amparo à Pesquisa do Estado de São Paulo
- National Institutes of Health
- National Institute of General Medical Sciences (GM 53836, R01GM053836)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Bacterial Genetics and Biotechnology
- Health Sciences › Medicine › Hematology › Iron Metabolism and Disorders
- Health Sciences › Medicine › Oncology › Drug Transport and Resistance Mechanisms
- Keywords
- FepA, TonB-dependent transport, beta-barrel membrane proteins, cysteine labeling, porin, functional complementation
- MeSH terms
- Bacterial Outer Membrane Proteins, Carrier Proteins, Colicins, Cysteine, Dose-Response Relationship, Drug, Enterobactin, Escherichia coli, Maleimides, Models, Molecular, Protein Conformation, Receptors, Cell Surface, Mutagenesis, Siderophores, Protein Structure, Secondary, Protein Structure, Tertiary, Porins, Fluorescein
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