Role of the TonB amino terminus in energy transduction between membranes

Jaskula, J C; Letain, Tracy E.; Roof, S K; Skare, Jon T.; Postle, Kathleen

doi:10.1128/jb.176.8.2326-2338.1994

Cited by 71 publications

(93 citation statements)

References 47 publications

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“…We have previously shown that TetA-TonB protein can be cross-linked to the outer membrane receptor FepA (Jaskula et al, 1994). Consistent with those observations, TetA-TonB was found to be associated with the outer membrane in sucrose density gradients.…”

Section: Discussionsupporting

confidence: 82%

“…Previous observations suggested that the latter is unlikely. First, TetA-TonB, which lacks the native TonB signal anchor, could associate with the outer membrane, and, as demonstrated previously, can be cross-linked to FepA (Jaskula et al, 1994) even though it is completely inactive, presumably due to the lack of its connection to the pmf. Second, DNP has no effect on the ability of TonB to cross-link to FepA in vivo (K. Postle and J. T. Skare, unpublished).…”

Section: Tonb Localizes With Both the Cytoplasmic And Outer Membranesmentioning

confidence: 72%

“…To determine whether or not this was the case, we fractionated cells that had been exposed to the protonophore DNP for 10 min or 1 h. Neither treatment affected the distribution of TonB in the gradients compared to untreated controls. This result was not entirely unanticipated because we have previously been able to cross-link TetA-TonB to the outer membrane receptor FepA (Jaskula et al, 1994) and, in the presence of DNP, to cross-link TonB to FepA (K. Postle and J. T. Skare, unpublished).…”

Section: Discussionmentioning

confidence: 99%

“…ᮊ 1997 Blackwell Science Ltd, Molecular Microbiology, 24, [271][272][273][274][275][276][277][278][279][280][281][282][283] Plasmids pBST324 (tetR plasmid, Kan R ; Allard and Bertrand, 1992), pKP321 (TetA-TonB expressed from the tetA promoter; Jaskula et al, 1994), pKP323 (pET24a with T7-tagged ExbD expressed from the T7 promoter), pKP339 (pET24a with T7-tagged ExbB expressed from the T7 promoter), pKP360 (pACYC184 expressing ExbB from the exb promoter), and pKP361 (pACYC184 expressing ExbD from the exb promoter) were used in this study. To construct pKP339 and pKP323, respectively, promoterless exbB or exbD genes were amplified by the polymerase chain reaction (PCR) and inserted into pET24a (Novagen) such that a T7-epitope tag was placed at the 5Ј end of the gene, and an intact stop codon was placed at the 3Ј end.…”

Section: Methodsmentioning

confidence: 99%

“…TonB protein is anchored in the cytoplasmic membrane by its uncleaved N-terminus, which serves as a signal anchor (Postle and Skare, 1988;Roof et al, 1991;Skare et al, 1989), a probable connection to the pmf (Jaskula et al, 1994), and a region of contact with one of the three transmembrane domains of ExbB (Karlsson et al, 1993a;Larsen et al, 1994;Traub et al, 1993). Although TonB has been localized to the cytoplasmic membrane by several groups (Hannavy et al, 1990;Plastow and Holland, 1979;Roof et al, 1991), its association with the outer membrane has never been investigated even though there have been numerous suggestions that such an interaction takes place (Bell et al, 1990;Braun et al, 1991;Gü nter and Braun, 1990;Reynolds et al, 1980;Schö ffler and Braun, 1989;Tuckman and Osburne, 1992), including the detection, by in vivo cross-linking, of direct physical interaction with the outer membrane receptor FepA (Skare et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

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TonB protein appears to transduce energy by shuttling between the cytoplasmic membrane and the outer membrane in Escherichia coli

Letain

Postle

1997

Molecular Microbiology

142

196

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SummaryThe energy source for active transport of iron-siderophore complexes and vitamin B12 across the outer membrane in Gram-negative bacteria is the cytoplasmic membrane proton-motive force (pmf). TonB protein is required in this process to transduce cytoplasmic membrane energy to the outer membrane. In this study, Escherichia coli TonB was found to be distributed in sucrose density gradients approximately equally between the cytoplasmic membrane and the outer membrane fractions, while two proteins with which it is known to interact, ExbB and ExbD, as well as the NADH oxidase activity characteristic of the cytoplasmic membrane, were localized in the cytoplasmic membrane fraction. Neither the N-terminus of TonB nor the cytoplasmic membrane pmf, both of which are essential for TonB activity, were required for TonB to associate with the outer membrane. When the TonB C-terminus was absent, TonB was found associated with the cytoplasmic membrane, suggesting that the C-terminus was required for outer membrane association. When ExbB and ExbD, as well as their cross-talk-competent homologues TolQ and TolR, were absent, TonB was found associated with the outer membrane. TetA-TonB protein, which cannot interact with ExbB/D, was likewise found associated with the outer membrane. These results indicated that the role of ExbB/D in energy transduction is to bring TonB that has reached the outer membrane back to associate with the cytoplasmic membrane. Two possible explanations exist for the observations presented in this study. One possibility is that TonB transduces energy by shuttling between membranes, and, at some stages in the energy-transduction cycle, is associated with either the cytoplasmic membrane or the outer membrane, but not with both at the same time. This hypothesis, together with the alternative interpretation that TonB remains localized in the cytoplasmic membrane and changes its affinity for the outer and cytoplasmic membrane during energy transduction, are incorporated with previous observations into two new models, consistent with the novel aspects of this system, that describe a mechanism for TonB-dependent energy transduction.

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Section: Discussionsupporting

confidence: 82%

Section: Tonb Localizes With Both the Cytoplasmic And Outer Membranesmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

TonB protein appears to transduce energy by shuttling between the cytoplasmic membrane and the outer membrane in Escherichia coli

Letain

Postle

1997

Molecular Microbiology

142

196

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Transmembrane α-Helix Interactions are Required for the Functional Assembly of theEscherichia coliTol Complex

Lazzaroni

Vianney

Popot

et al. 1995

Journal of Molecular Biology

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The Tol/PAL and TonB systems : two envelope-spanning protein complexes involved in colicin import in E. coli.

Bouveret¹,

Lazdunski²,

Bénédetti³

1996

Molecular Dynamics of Biomembranes

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Mutants in tolA, B, Q, and R genes have been isolated on the basis of their tolerance to bacterial toxins (colicins) and their resistance to the infection of filamentous phages (M13, fd, and f1) Reeves, 1975a, 1975b;Nagel de Zwaig and Luria, 1967). These genes form a cluster at 16,8 min on the chromosomal map of E. coli. tol mutants are hypersensitive to detergents and to certain drugs, and they release periplasmic proteins into the growth medium (Nagel de Zwaig and Luria, 1967). Mutations in a contiguous gene, pal, which encodes the outer membrane Peptidoglycan Associated Lipoprotein (PAL), generate a similar phenotype (FogniniLefebvre et aI., 1987). This suggests that the TollPAL proteins are involved in maintaining the integrity of the outer membrane of E. coli. However, the exact physiological role of the TollPAL system has not yet been elucidated.After colicins have been released from producing bacteria, they bind to specific receptors at the surface of sensitive bacteria, translocate through the cell envelope and kill them. However, colicins are too large to freely pass through the outer membrane barrier. The toxins and a variety of bacteriophages have taken advantage of resident envelope proteins to enter bacteria. Group B colicins (including B, D, la, lb, M, and 5) and phages T1 and <1>80 have parasitized TonB and its associated proteins ExbB and ExbD. The role of these proteins, in association with specific receptors of the outer membrane, is to promote the active transport of vitamin B12 and iron siderophores through the outer membrane. Group A colicins (A, El to E9, K, L, N, and 10) and phages f1, fd, and M 13 have parasitized the Tol proteins. The sequences and the localizations of the TollPAL proteins and the proteins of the TonB system have been determined. In addition, the topologies of the inner membrane anchored proteins have been elucidated. Recently, it has been demonstrated that both systems form a complex and the interactions involved between the different components are on the way to be characterized.The present paper reviews these recent data with emphasis on the Tol proteins and the more recent contribution from the authors' laboratory. We also report the recent progress in the understanding of the translocation step of colicins and describe the approach we are now following to try to fully elucidate the translocation mechanism of group A colicins. Here, we report and discuss recent progresses in these studies.

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Role of the TonB amino terminus in energy transduction between membranes

Cited by 71 publications

References 47 publications

TonB protein appears to transduce energy by shuttling between the cytoplasmic membrane and the outer membrane in Escherichia coli

TonB protein appears to transduce energy by shuttling between the cytoplasmic membrane and the outer membrane in Escherichia coli

Transmembrane α-Helix Interactions are Required for the Functional Assembly of theEscherichia coliTol Complex

The Tol/PAL and TonB systems : two envelope-spanning protein complexes involved in colicin import in E. coli.

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