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Gene Review

tonB  -  transport protein TonB

Escherichia coli CFT073

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Disease relevance of tonB


High impact information on tonB

  • Sequence homologies and mutagenesis data are used to propose a structural mechanism for TonB-dependent siderophore-mediated transport across the outer membrane [3].
  • The sequence homology among TonB-dependent proteins suggests that all ligand-specific outer membrane receptors may function by this gated-porin mechanism [6].
  • Point mutants in FecA displayed the constitutive expression of fec transport genes in the absence of ferric citrate but still required TonB, with the exception of one FecA mutant which showed a TonB-independent induction [7].
  • A characteristic feature of TonB-dependent transporters is the Ton box, a conserved sequence near the N terminus and exposed to the periplasm [8].
  • In TonB-dependent transporters, a conserved sequence of seven residues, the Ton box, faces the periplasm and interacts with the inner membrane TonB protein to energize an active transport cycle [9].

Chemical compound and disease context of tonB

  • The predicted NH2 terminus of tonB protein resembles the proteolytically cleaved signal sequences of E. coli periplasmic and outer membrane proteins; the overall hydrophilic character of the protein sequence suggests that the bulk of the tonB protein is not embedded within the inner or outer membrane [10].
  • Nucleotide sequence of the gene for the ferrienterochelin receptor FepA in Escherichia coli. Homology among outer membrane receptors that interact with TonB [11].
  • The conserved proline-rich motif is not essential for energy transduction by Escherichia coli TonB protein [12].
  • In contrast to the TonB proteins of E. coli and Salmonella typhimurium, translation of the S. marcescens TonB protein starts at the first methionine residue of the open reading frame, which is the only amino acid removed during TonB maturation and export [13].
  • Tandem duplication of the E. coli (EP)X(KP) region by insertion of the S. marcescens (EP)X(KP) region (38 residues) and replacement of lysine residue 91 by glutamate did not alter TonB activity so that no evidence was obtained for this region to be implicated in receptor binding [14].

Biological context of tonB

  • The molecular characterization of the mutation that corrected the Eut- phenotype caused by allele Delta903 showed that the new mutation was a deletion of two nucleotides at the tonB-trpA fusion site [2].
  • The receptor-binding domain of TonB appears to be formed by a highly conserved C-terminal amino acid sequence of approximately 100 residues [15].
  • To accomplish energy transfer, TonB contacts outer membrane receptors [16].
  • TonB-dependent transducers might be important for pathogenicity; therefore, a survey of their presence in bacteria was aimed [17].
  • Point mutations were introduced into the TonB-box region of the colicin B structural gene cba resulting in colicin B derivatives which were partially or totally inactive against E. coli cells [18].

Anatomical context of tonB


Associations of tonB with chemical compounds

  • Interaction between TonB and two of the TonB-dependent siderophore transporters has been detected previously by formaldehyde crosslinking [24].
  • A significant discrepancy exists between the calculated size of tonB protein and the apparent size of 36 kilodaltons determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis [10].
  • TonB also possesses two distinct binding regions: one in the C terminus of the protein, for which binding to FhuA is ferricrocin-independent, and a higher affinity region outside the C terminus, for which ferricrocin enhances interactions with FhuA [16].
  • FhuD residue Thr-181, located within the siderophorebinding site and mapping to a predicted TonB-interaction surface, was mutated to cysteine [25].
  • In this report, we show, by Edman degradation of [35S]methionine-labeled protein, that TonB protein synthesized in vitro initiates at the third of these methionine codons [26].

Analytical, diagnostic and therapeutic context of tonB

  • In this study, analyses of FhuA interactions with two recombinant TonB proteins by analytical ultracentrifugation revealed that TonB forms a 2:1 complex with FhuA [16].
  • The PCR mutagenesis strategy targeted the N-terminus because it forms a plug inside the FepA barrel that is expected to be involved in ligand binding, ligand transport, and interaction with TonB [27].
  • Purified FhuA peptides fused to MBP bound specifically to TonB by ELISA [28].
  • Further, site-directed mutagenesis of the TonB box -1 residue in a V. cholerae TonB2-dependent receptor demonstrated that a large hydrophobic amino acid in this position promotes recognition of V. cholerae TonB1 [29].
  • On the basis of the multiple progressive sequence alignment and the similarity scores derived from it, a tree representing evolutionary distance between five TonB-dependent outer membrane transport proteins was generated [30].


  1. Characterization of ferric and ferrous iron transport systems in Vibrio cholerae. Wyckoff, E.E., Mey, A.R., Leimbach, A., Fisher, C.F., Payne, S.M. J. Bacteriol. (2006) [Pubmed]
  2. Molecular characterization of eutF mutants of Salmonella typhimurium LT2 identifies eutF lesions as partial-loss-of-function tonB alleles. Thomas, M.G., O'Toole, G.A., Escalante-Semerena, J.C. J. Bacteriol. (1999) [Pubmed]
  3. Siderophore-mediated iron transport: crystal structure of FhuA with bound lipopolysaccharide. Ferguson, A.D., Hofmann, E., Coulton, J.W., Diederichs, K., Welte, W. Science (1998) [Pubmed]
  4. Ligand-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., Klebba, P.E. Science (1997) [Pubmed]
  5. Hemin uptake system of Yersinia enterocolitica: similarities with other TonB-dependent systems in gram-negative bacteria. Stojiljkovic, I., Hantke, K. EMBO J. (1992) [Pubmed]
  6. 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. Science (1992) [Pubmed]
  7. Signal transfer through three compartments: transcription initiation of the Escherichia coli ferric citrate transport system from the cell surface. Härle, C., Kim, I., Angerer, A., Braun, V. EMBO J. (1995) [Pubmed]
  8. Differential substrate-induced signaling through the TonB-dependent transporter BtuB. Cadieux, N., Phan, P.G., Cafiso, D.S., Kadner, R.J. Proc. Natl. Acad. Sci. U.S.A. (2003) [Pubmed]
  9. Substrate-induced transmembrane signaling in the cobalamin transporter BtuB. Chimento, D.P., Mohanty, A.K., Kadner, R.J., Wiener, M.C. Nat. Struct. Biol. (2003) [Pubmed]
  10. DNA sequence of the Escherichia coli tonB gene. Postle, K., Good, R.F. Proc. Natl. Acad. Sci. U.S.A. (1983) [Pubmed]
  11. Nucleotide sequence of the gene for the ferrienterochelin receptor FepA in Escherichia coli. Homology among outer membrane receptors that interact with TonB. Lundrigan, M.D., Kadner, R.J. J. Biol. Chem. (1986) [Pubmed]
  12. The conserved proline-rich motif is not essential for energy transduction by Escherichia coli TonB protein. Larsen, R.A., Wood, G.E., Postle, K. Mol. Microbiol. (1994) [Pubmed]
  13. The tonB gene of Serratia marcescens: sequence, activity and partial complementation of Escherichia coli tonB mutants. Gaisser, S., Braun, V. Mol. Microbiol. (1991) [Pubmed]
  14. Activity domains of the TonB protein. Traub, I., Gaisser, S., Braun, V. Mol. Microbiol. (1993) [Pubmed]
  15. Crystal structure of a 92-residue C-terminal fragment of TonB from Escherichia coli reveals significant conformational changes compared to structures of smaller TonB fragments. Ködding, J., Killig, F., Polzer, P., Howard, S.P., Diederichs, K., Welte, W. J. Biol. Chem. (2005) [Pubmed]
  16. Enhanced binding of TonB to a ligand-loaded outer membrane receptor: role of the oligomeric state of TonB in formation of a functional FhuA.TonB complex. Khursigara, C.M., De Crescenzo, G., Pawelek, P.D., Coulton, J.W. J. Biol. Chem. (2004) [Pubmed]
  17. TonB-dependent trans-envelope signalling: the exception or the rule? Koebnik, R. Trends Microbiol. (2005) [Pubmed]
  18. Import-defective colicin B derivatives mutated in the TonB box. Mende, J., Braun, V. Mol. Microbiol. (1990) [Pubmed]
  19. Energy-coupled transport and signal transduction through the gram-negative outer membrane via TonB-ExbB-ExbD-dependent receptor proteins. Braun, V. FEMS Microbiol. Rev. (1995) [Pubmed]
  20. Energy transduction between membranes. TonB, a cytoplasmic membrane protein, can be chemically cross-linked in vivo to the outer membrane receptor FepA. Skare, J.T., Ahmer, B.M., Seachord, C.L., Darveau, R.P., Postle, K. J. Biol. Chem. (1993) [Pubmed]
  21. TonB-dependent systems of uropathogenic Escherichia coli: aerobactin and heme transport and TonB are required for virulence in the mouse. Torres, A.G., Redford, P., Welch, R.A., Payne, S.M. Infect. Immun. (2001) [Pubmed]
  22. Contribution of TonB- and Feo-mediated iron uptake to growth of Salmonella typhimurium in the mouse. Tsolis, R.M., Bäumler, A.J., Heffron, F., Stojiljkovic, I. Infect. Immun. (1996) [Pubmed]
  23. Crystallization and preliminary X-ray analysis of a C-terminal TonB fragment from Escherichia coli. Koedding, J., Polzer, P., Killig, F., Howard, S.P., Gerber, K., Seige, P., Diederichs, K., Welte, W. Acta Crystallogr. D Biol. Crystallogr. (2004) [Pubmed]
  24. Site-directed disulfide bonding reveals an interaction site between energy-coupling protein TonB and BtuB, the outer membrane cobalamin transporter. Cadieux, N., Kadner, R.J. Proc. Natl. Acad. Sci. U.S.A. (1999) [Pubmed]
  25. Interactions between TonB from Escherichia coli and the Periplasmic Protein FhuD. Carter, D.M., Miousse, I.R., Gagnon, J.N., Martinez, E., Clements, A., Lee, J., Hancock, M.A., Gagnon, H., Pawelek, P.D., Coulton, J.W. J. Biol. Chem. (2006) [Pubmed]
  26. Escherichia coli TonB protein is exported from the cytoplasm without proteolytic cleavage of its amino terminus. Postle, K., Skare, J.T. J. Biol. Chem. (1988) [Pubmed]
  27. Mutations in the Escherichia coli receptor FepA reveal residues involved in ligand binding and transport. Barnard, T.J., Watson, M.E., McIntosh, M.A. Mol. Microbiol. (2001) [Pubmed]
  28. Phage display reveals multiple contact sites between FhuA, an outer membrane receptor of Escherichia coli, and TonB. Carter, D.M., Gagnon, J.N., Damlaj, M., Mandava, S., Makowski, L., Rodi, D.J., Pawelek, P.D., Coulton, J.W. J. Mol. Biol. (2006) [Pubmed]
  29. Analysis of residues determining specificity of Vibrio cholerae TonB1 for its receptors. Mey, A.R., Payne, S.M. J. Bacteriol. (2003) [Pubmed]
  30. Evolutionary relationship between the TonB-dependent outer membrane transport proteins: nucleotide and amino acid sequences of the Escherichia coli colicin I receptor gene. Nau, C.D., Konisky, J. J. Bacteriol. (1989) [Pubmed]
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