Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores

Wooldridge, Karl G.; Morrissey, Julie A.; Williams, Peter H.

doi:10.1099/00221287-138-3-597

Cited by 20 publications

(14 citation statements)

References 45 publications

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“…The available evidence indicates that Cbl is actively transported across the outer membrane and that the TonB protein functions in energy transduction, coupling outer membrane transport to the consumption of the respiratory proton gradient across the inner membrane. It is reasonable to conclude that the TonB-dependent transport systems for the ferric siderophores are also outer membrane pumps, a conclusion that is supported by the demonstration by Wooldridge et al (26) that ferric aerobactin is actively transported across the outer membrane of E. coli. On the other hand, a recent report by Rutz et al (20) has suggested that the TonB-dependent transport systems are gated channels, which implies facilitated diffusion, but it should be noted that their results with FepA do not, in fact, rule out active transport as the mechanism of outer membrane transport of ferric enterobactin.…”

Section: Discussionmentioning

confidence: 76%

The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli

1993

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Cells of Escherichia coli pump cobalamin (vitamin B12) across their outer membranes into the periplasmic space, and it was concluded previously that this process is potentiated by the proton motive force of the inner membrane. The novelty of such an energy coupling mechanism and its relevance to other outer membrane transport processes have required confirmation of this conclusion by studies with cells in which cobalamin transport is limited to the outer membrane. Accordingly, I have examined the effects of cyanide and of 2,4-dinitrophenol on cobalamin uptake in btuC and atp mutants, which lack inner membrane cobalamin transport and the membrane-bound ATP synthase, respectively. Dinitrophenol eliminated cobalamin transport in all strains, but cyanide inhibited this process only in atp and btuC atp mutant cells, providing conclusive evidence that cobalamin transport across the outer membrane requires specifically the proton motive force of the inner membrane. The coupling of metabolic energy to outer membrane cobalamin transport requires the TonB protein and is stimulated by the ExbB protein. I show here that the tolQ gene product can partly replace the function of the ExbB protein. Cells with mutations in both exbB and tolQ had no measurable cobalamin transport and thus had a phenotype that was essentially the same as TonB-. I conclude that the ExbB protein is a normal component of the energy coupling system for the transport of cobalamin across the outer membrane.

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Section: Discussionmentioning

confidence: 76%

The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli

1993

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“…In E. coli, the energy transduction process requires direct contact between TonB and OM receptors. This in turn leads to translocation of the associated ferri-siderophore to the periplasm and de-energisation of TonB [32,33]. Substitutions in this region inactivate the transport capability of the corresponding receptor, but such e¡ects can be reversed by complementary substitutions in TonB suggesting that the TonB box region, thought to be located in the periplasm, physically interacts with the TonB protein.…”

Section: The Tonb-exbb-exbd Complexmentioning

confidence: 99%

“…It is believed that ExbB and ExbD use the mem- brane electro-chemical charge gradient to produce an 'energised' form of TonB that mediates a conformational change in the liganded OM receptor. This in turn leads to translocation of the associated ferri-siderophore to the periplasm and de-energisation of TonB [32,33]. The deenergised form of TonB then 'recycles' back to the CM [34,35].…”

Section: The Tonb-exbb-exbd Complexmentioning

confidence: 99%

Bacterial iron homeostasis

2003

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Iron is essential to virtually all organisms, but poses problems of toxicity and poor solubility. Bacteria have evolved various mechanisms to counter the problems imposed by their iron dependence, allowing them to achieve effective iron homeostasis under a range of iron regimes. Highly efficient iron acquisition systems are used to scavenge iron from the environment under iron-restricted conditions. In many cases, this involves the secretion and internalisation of extracellular ferric chelators called siderophores. Ferrous iron can also be directly imported by the G protein-like transporter, FeoB. For pathogens, host-iron complexes (transferrin, lactoferrin, haem, haemoglobin) are directly used as iron sources. Bacterial iron storage proteins (ferritin, bacterioferritin) provide intracellular iron reserves for use when external supplies are restricted, and iron detoxification proteins (Dps) are employed to protect the chromosome from iron-induced free radical damage. There is evidence that bacteria control their iron requirements in response to iron availability by down-regulating the expression of iron proteins during iron-restricted growth. And finally, the expression of the iron homeostatic machinery is subject to iron-dependent global control ensuring that iron acquisition, storage and consumption are geared to iron availability and that intracellular levels of free iron do not reach toxic levels.

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“…This might allow TonB to contact specific regions on the receptor. It appears that "energized" TonB is then able to deliver its energy to the receptor, resulting in ligand translocation into the periplasm (10,11). ExbB⅐ExbD are implicated in the recycling of TonB, from its high affinity OM receptor association to a high affinity inner membrane association (12,13).…”

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confidence: 99%

Crystal Structure of the Dimeric C-terminal Domain of TonB Reveals a Novel Fold

Chang¹,

Mooser²,

Plückthun³

et al. 2001

Journal of Biological Chemistry

120

144

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The TonB-dependent complex of Gram-negative bacteria couples the inner membrane proton motive force to the active transport of iron⅐siderophore and vitamin B 12 across the outer membrane. The structural basis of that process has not been described so far in full detail. The crystal structure of the C-terminal domain of TonB from Escherichia coli has now been solved by multiwavelength anomalous diffraction and refined at 1.55-Å resolution, providing the first evidence that this region of TonB (residues 164 -239) dimerizes. Moreover, the structure shows a novel architecture that has no structural homologs among any known proteins. The dimer of the C-terminal domain of TonB is cylinder-shaped with a length of 65 Å and a diameter of 25 Å. Each monomer contains three ␤ strands and a single ␣ helix. The two monomers are intertwined with each other, and all six ␤-strands of the dimer make a large antiparallel ␤-sheet. We propose a plausible model of binding of TonB to FhuA and FepA, two TonB-dependent outer-membrane receptors.The outer membrane (OM 1 ) of Gram-negative bacteria constitutes a permeability barrier, protecting the cell against a variety of toxic agents. The lipopolysaccharides located in the outer leaflet of the OM confer to the bacteria a polar and negatively charged surface, restricting the cellular uptake of toxic organic molecules and detergents such as bile salts, the detergents in the gut. However, although the OM is an effective protective barrier against harmful environmental components, it also represents an additional obstacle for the uptake of nutrients, which can be circumvented in three ways. While small hydrophilic nutrients (Ͻ600 Da) enter the periplasm by simple diffusion through porins in a non-selective manner (1), larger molecules are taken up by pores with an internal binding site for the ligand (such as LamB) in a stereospecific and selective manner (2) and can subsequently enter the cytoplasm by a variety of transporters located in the inner membrane (3). A few nutrients, notably iron and vitamin B 12 , need to be taken up into the periplasm against their concentration gradients.For this purpose, a complex consisting of TonB, ExbB, and ExbD couples the inner membrane proton motive force (pmf) to the active transport of iron siderophores and vitamin B 12 across the OM through specialized porins. Recently, crystal structures were solved for two TonB-dependent receptors, . Like all other known porins, they are ␤-barrels, but unlike the other porin structures they have much larger interiors, which are almost completely obscured by a protein domain sitting inside the barrel (termed the "cork" or "hatch region"), which is encoded within the N-terminal segment of either protein.Iron uptake into bacteria is initiated by the binding of the iron⅐siderophore complex to the high affinity OM receptor. The dissociation constant is around 100 -200 nM (7,8). An electron spin resonance study (9), later rationalized by three-dimensional structural models (4 -6), has shown that this event triggers conf...

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Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores

Cited by 20 publications

References 45 publications

The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli

The proton motive force drives the outer membrane transport of cobalamin in Escherichia coli

Bacterial iron homeostasis

Crystal Structure of the Dimeric C-terminal Domain of TonB Reveals a Novel Fold

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