1887

Chapter 7 : The TonB, ExbB, and ExbD Proteins

MyBook is a cheap paperback edition of the original book and will be sold at uniform, low price.

Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase

Buy this Chapter
Digital (?) $15.00

Preview this chapter:
Zoom in
Zoomout

The TonB, ExbB, and ExbD Proteins, Page 1 of 2

| /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap07-1.gif /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap07-2.gif

Abstract:

The proton motive force (PMF) of the cytoplasmic membrane is harnessed as the energy source. This spatial separation of the energy source from the energy sink necessitates an intermediate linkage between the two processes. That function is fulfilled by three proteins, TonB, ExbB, and ExbD, that couple the cytoplasmic membrane PMF to the active transport of nutrients through outer membrane transporters. This chapter focuses on our current understanding of the means by which energy is harvested at the cytoplasmic membrane and delivered to the outer membrane transporters in , and then reviews some of the diversity in this system that has recently become apparent. Based on evidence to date, it is reasonable to consider TonB to consist of three distinct functional domains: the amino-terminal domain, the central domain, and the carboxy-terminal domain. The ability of cells to transport cobalamin and various iron-siderophore complexes and their susceptibility to killing by bacteriophages and colicins are routinely used in assays to characterize phenotypes of mutant proteins in the TonB-dependent energy transduction system.

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7

Key Concept Ranking

Outer Membrane Proteins
0.46112633
0.46112633
Highlighted Text: Show | Hide
Loading full text...

Full text loading...

Figures

Image of FIGURE 1
FIGURE 1

Predicted topologies of TonB, ExbB, and ExbD in the cytoplasmic membrane. The locations of the periplasm and cytoplasm are indicated. Parentheses indicate alternative designations for transmembrane domains. Reprinted from Postle and Kadner (2003) with permission from the publisher.

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 2
FIGURE 2

Relative sensitivity windows for commonly used assays of TonB function. Cells expressing functional TonB at either wild-type (100%) or lower (12% or 0.4% or absent) levels were examined, and the results are summarized here. The black region indicates the range of TonB activity that a given assay can clearly distinguish. For example, colicin sensitivity can clearly distinguish between TonB activity levels of 0, 0.4, and 12%. The transition from gray to white indicates the portion of the sensitivity window in which the end point is unclear; for example, colicin sensitivity can distinguish between 12 and 100%, but levels intermediate between these values have not been tested. A gray zone is not depicted for enterochelin hypersecretion due to the overall insensitivity of this assay. Note that the 0.4% level corresponds approximately to a single copy of TonB per cell. Enterochelin secretion was measured as a zone of clearing on CAS (Chrome azurol S) indicator plates. Transport includes both [Fe] derophore uptake and irreversible φ80 adsorption assays. Colicin sensitivity is based on spot titer assays with the TonB-dependent colicins B, D, Ia, and M. Phage sensitivity is based on spot titer assays with φ80. B-dependent growth was measured by the ability of strains to grow in the presence of vitamin B.

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 3
FIGURE 3

Crystal structure of the C-terminal 75 residues of TonB, with positions of all aromatic residues indicated in the dimer. Modified from Chang et al. (2001) and reprinted from Ghosh and Postle (2004) with permission from the publisher.

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 4
FIGURE 4

Conservation in the TonB transmembrane domain. Sequences are presented relative to residues 11 to 33 of TonB, the predicted transmembrane domain (TMD) of which residues 12 to 32 are indicated by the bar at the top. The corresponding region from the TonB analog TolA is included for two species at the base of the figure. Shading indicates conserved aa in the SHLS motif. The NCBI accession numbers for the sequences presented are as follows: TonB sequences: (BVEC), (NP_405736), (AAK08071), (Q05613), (CAB53383), (O06432), (NP_246125), (P42872), (AAG23396), TonB1 (O052042) TonB2 (AAC69456); To1A sequences: (NP_415267), (NP_231471).

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 5
FIGURE 5

The C-terminal region of “extra” TonB proteins differs from that of “classic” TonB. Sequences are presented relative to residues 11 to 33 of TonB as in Fig. 4 and to residues 160 to 234 of the carboxy-terminal region of TonB. In the TMD region, only the conserved S and H residues are shaded. In the remainder, the shading indicates regions of significant residue homology. The NCBI accession numbers for the sequences presented are as follows: TonB (BVEC), TonB (P26185), . TonB1 (O052042), TonB2 (AAC69456), CjrB (AAK67306), HasB (sequence provided by C. Wandersman).

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 6
FIGURE 6

Conservation in the ExbB TMDs. Sequences are presented relative to residues 15 to 41 and 126 to 196 of ExbB, with the predicted TMDs indicated at the top. ExbB sequences are divided into two groups primarily on the basis of differences in TMD number 1. The corresponding region from the ExbB homolog TolQ is included for two species at the base of the figure, as is flagellar motor protein MotA. The shading indicates regions of significant residue homology. The NCBI accession numbers for the sequences presented are as follows: ExbB sequences: (NP_417479), (NP_404318), (AAK08069), (S28442), (T44782), (AAC45287), (NP_246123), (NP_438422), (AAG23397), ExbB1 (O025897), ExbB2 (AAC69454); TolQ sequences: (NP–308799), (NP_231473); MotA sequence: (NP_389252).

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of FIGURE 7
FIGURE 7

Conservation in the ExbD TMDs and C terminus. Sequences are presented relative to residues 18 to 44 and 100 to 136 of ExbD, with the predicted TMD indicated at the top. The corresponding region from the ExbD homolog TolR is included for two species at the base of the figure, as is flagellar motor protein MotB. The shading indicates regions of significant residue homoPgy. The NCBI accession numbers for the sequences presented are as follows: ExbD sequences: (NP_417478), (NP_404319), (AAK08070), (AAK70857), (T44783), (O06434), (NP_246124), (NP_438421), (AAG23398), ExbD1 (O52044), ExbD2 (Q9ZHV9); TolR sequences: (P05829), (NP_231472), MotB sequence: (P28612).

Citation: Postle K, Larsen R. 2004. The TonB, ExbB, and ExbD Proteins, p 96-112. In Crosa J, Mey A, Payne S, Iron Transport in Bacteria. ASM Press, Washington, DC. doi: 10.1128/9781555816544.ch7
Permissions and Reprints Request Permissions
Download as Powerpoint

References

/content/book/10.1128/9781555816544.chap7
1. Barnard, T. J.,, M. E. Watson, Jr.,, and M. A. Mc- Intosh. 2001. Mutations in the Escherichia coli receptor FepA reveal residues involved in ligand binding and transport. Mol. Microbiol. 41:527536.
2. Bradbeer, C. 1993. The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli. J. Bacteriol. 175:1463150.
3. Braun, M.,, F. Endriss,, H. Killmann,, and V. Braun. 2003. In vivo reconstitution of the FhuA transport protein of Escherichia coli K-12. J. Bacteriol. 185:55085518.
4. Braun, M.,, H. Killmann,, and V. Braun. 1999. The beta-barrel domain of FhuADelta5-160 is sufficient for TonB-dependent FhuA activities of Escherichia coli. Mol. Microbiol. 33:10371049.
5. Braun, V.,, S. Gaisser,, C. Herrman,, K. Kampfenkel,, H. Killman,, and I. Traub. 1996. Energy-coupled transport across the outer membrane of Escherichia coli: ExbB binds ExbD and TonB in vitro, and leucine 132 in the periplasmic region and aspartate 25 in the transmembrane region are important for ExbD activity. J. Bacteriol. 178:28362845.
6. Braun, V.,, and C. Herrmann. 1993. Evolutionary relationship of uptake systems for biopolymers in Escherichia coli: cross-complementation between the TonB-ExbB-ExbD and the TolA-TolQ-TolR proteins. Mol. Microbiol. 8:261268.
7. Braun, V.,, S. I. Patzer,, and K. Hantke. 2002. Ton-dependent colicins and microcins: modular design and evolution. Biochimie 84:365380.
8. Cadieux, N.,, and R. J. Kadner. 1999. Site-directed disulfide bonding reveals an interaction site between energy-coupling protein TonB and BtuB, the outer membrane cobalamin transporter. Proc. Natl. Acad. Sci. USA 96:1067310678.
9. Cascales, E.,, R. Lloubes,, and J. N. Sturgis. 2001. The TolQ-TolR proteins energize TolA and share homologies with the flagellar motor proteins MotAMotB. Mol. Microbiol. 42:795807.
10. Chang, C.,, A. Mooser,, A. Pluckthun,, and A. Wlodawer. 2001. Crystal structure of the dimeric C-terminal domain of TonB reveals a novel fold. J. Biol. Chem. 276:2753527540.
11. Fischer, E.,, K. Günter,, and V. Braun. 1989. Involvement of ExbB and TonB in transport across the outer membrane of Escherichia coli: phenotypic complementation of exb mutants by over-expressed tonB and physical stabilization of TonB by ExbB. J. Bacteriol. 171:51275134.
12. Ghosh, J.,, and K. Postle. 2004. Evidence for dynamic clustering of carboxy-terminal aromatic amino acids in TonB-dependent energy transduction. Mol. Microbiol. 51:203213.
13. Ghosh, J.,, and K. Postle. Disulfide trapping of an in vivo energy transducing conformation of Escherichia coli TonB protein. Submitted for publication.
14. Higgs, P. I.,, R. A. Larsen,, and K. Postle. 2002. Quantitation of known components of the Escherichia coli TonB-dependent energy transduction system: TonB, ExbB, ExbD, and FepA. Mol. Microbiol. 44:271281.
15. Higgs, P. I.,, T. E. Letain,, K. K. Merriam,, N. S. Burke,, H. Park,, C. Kang,, and K. Postle. 2002. TonB interacts with nonreceptor proteins in the outer membrane of Escherichia coli. J. Bacteriol. 184: 16401648.
16. Kampfenkel, K.,, and V. Braun. 1993. Topology of the ExbB protein in the cytoplasmic membrane of Escherichia coli. J. Biol. Chem. 268:60506057.
17. Karlsson, M.,, K. Hannavy,, and C. F. Higgins. 1993. ExbB acts as a chaperone-like protein to stabilize TonB in the cytoplasm. Mol. Microbiol. 8: 389396.
18. Larsen, R. A.,, G. J. Chen,, and K. Postle. 2003. Performance of standard phenotypic assays for TonB activity, as evaluated by varying the level of functional, wild-type TonB. J. Bacteriol. 185: 46994706.
19. Larsen, R. A.,, T. E. Letain,, and K. Postle. 2003. In vivo evidence of TonB shuttling between the cytoplasmic and outer membrane in Escherichia coli. Mol. Microbiol. 49:211218.
20. Larsen, R. A.,, M. G. Thomas,, and K. Postle. 1999. Protonmotive force, ExbB and ligand-bound FepA drive conformational changes in TonB. Mol. Microbiol. 31:18091824.
21. Larsen, R. A.,, G. E. Wood,, and K. Postle. 1993. The conserved proline-rich motif is not essential for energy transduction by Escherichia coli TonB protein. Mol. Microbiol. 10:943953.
22. Letain, T. E.,, and K. Postle. 1997. TonB protein appears to transduce energy by shuttling between the cytoplasmic membrane and the outer membrane in Gram-negative bacteria. Mol. Microbiol. 24: 271283.
23. Liu, J.,, J. M. Rutz,, P. E. Klebba,, and J. B. Feix. 1994. Site-directed spin-labeling study of ligand-induced conformational change in the ferric enterobactin receptor, FepA. Biochemistry 33: 1327413283.
24. Mann, B. J.,, C. D. Holroyd,, C. Bradbeer,, and R. J. Kadner. 1986. Reduced activity of TonB-dependent functions in strains of Escherichia coli. FEMS Microbiol. Lett. 33:255260.
25. Mey, A. R.,, and S. M. Payne. 2003. Analysis of residues determining specificity of Vibrio cholerae TonB1 for its receptors. J. Bacteriol. 185:11951207.
26. Moeck, G. S.,, P. Tawa,, H. Xiang,, A. A. Ismail,, J. L. Turnbull,, and J. W. Coulton. 1996. Ligand-induced conformational change in the ferrichromeiron receptor of Escherichia coli K-12. Mol. Microbiol. 22:459471.
27. Moeck, G. S.,, J. W. Coulton,, and K. Postle. 1997. Cell envelope signaling in Escherichia coli. Ligand binding to the ferrichrome-iron receptor FhuA promotes interaction with the energy-transducing protein TonB. J. Biol. Chem. 272:2839128397.
28. Occhino, D. A.,, E. E. Wyckoff,, D. P. Henderson,, T. J. Wrona,, and S. M. Payne. 1998. Vibrio cholerae iron transport: haem transport genes are linked to one of two sets of tonB, exbB, exbD genes. Mol. Microbiol. 29:14931507.
29. Postle, K.,, and R. J. Kadner. 2003. Touch and go: tying TonB to transport. Mol. Microbiol. 49: 869882.
30. Sauter, A.,, S. P. Howard,, and V. Braun. 2003. In vivo evidence for TonB dimerization. J. Bacteriol. 185:57475754.
31. Scott, D. C.,, Z. Cao,, Z. Qi,, M. Bauler,, J. D. Igo,, S. M. Newton,, and P. E. Klebba. 2001. Exchangeability of N termini in the ligand-gated porins of Escherichia coli. J. Biol. Chem. 276: 1302513033.
32. Seliger, S. S.,, A. R. Mey,, A. M. Valle,, and S. M. Payne. 2001. The two TonB systems of Vibrio cholerae: redundant and specific functions. Mol. Microbiol. 39:801812.
33. Smajs, D.,, and G. M. Weinstock. 2001. The iron and temperature-regulated cjrBC genes of Shigella and enteroinvasive Escherichia coli strains code for colicin Js uptake. J. Bacteriol. 183:39583966.
34. Vakharia, H. L.,, and K. Postle. 2002. FepA with globular domain deletions lacks activity. J. Bacteriol. 184:55085512.
35. Young, G. M.,, and K. Postle. 1994. Repression of tonB transcription during anaerobic growth requires Fur binding at the promoter and a second factor binding upstream. Mol. Microbiol. 11:943954.

This is a required field
Please enter a valid email address
Please check the format of the address you have entered.
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error