Evolutionary relationship of uptake systems for biopolymers in <i>Escherichia coli</i>: cross‐complementation between the TonB‐ExbB‐ExbD and the TolA‐TolQ‐TolR proteins

Braun, Volkmar; Herrmann, Christina

doi:10.1111/j.1365-2958.1993.tb01570.x

Cited by 156 publications

(162 citation statements)

References 30 publications

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“…A monomeric form of this proposed topology was also found in the crystal structure of TolA, a protein functionally related to TonB from the TolA⅐TolQ⅐TolR protein complex (49). The three-dimensional structure of the C-terminal domain of TolA from E. coli in complex with g3p (50) shows a very similar fold to the three-dimensional structure of the same domain of TolA from P. aeruginosa (31) despite an amino acid sequence identity of only 20%.…”

Section: Discussionmentioning

confidence: 61%

Dimerization of TonB Is Not Essential for Its Binding to the Outer Membrane Siderophore Receptor FhuA of Escherichia coli

Koedding

Howard

Kaufmann

et al. 2004

Journal of Biological Chemistry

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FhuA belongs to a family of specific siderophore transport systems located in the outer membrane of Escherichia coli. The energy required for the transport process is provided by the proton motive force of the cytoplasmic membrane and is transmitted to FhuA by the protein TonB. Although the structure of full-length TonB is not known, the structure of the last 77 residues of a fragment composed of the 86 C-terminal amino acids was recently solved and shows an intertwined dimer (Chang, C., Mooser, A., Pluckthun, A., and Wlodawer, A. (2001) J. Biol. Chem. 276, 27535-27540). We analyzed the ability of truncated C-terminal TonB fragments of different lengths (77, 86, 96, 106, 116, and 126 amino acid residues, respectively) to bind to the receptor FhuA. Only the shortest TonB fragment, TonB-77, could not effectively interact with FhuA. We have also observed that the fragments TonB-77 and TonB-86 form homodimers in solution, whereas the longer fragments remain monomeric. TonB fragments that bind to FhuA in vitro also inhibit ferrichrome uptake via FhuA in vivo and protect cells against attack by bacteriophage ⌽80.

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Section: Discussionmentioning

confidence: 61%

Dimerization of TonB Is Not Essential for Its Binding to the Outer Membrane Siderophore Receptor FhuA of Escherichia coli

Koedding

Howard

Kaufmann

et al. 2004

Journal of Biological Chemistry

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“…The 15.2 kDa protein encoded by the third ORF had the highest homology with E. coli TolR (Table 1). This protein had a hydropathy profile similar to that of E. coli ExbD (Braun and Herrmann, 1993), but its homology to E. coli ExbD was weak. This protein is designated as the V. cholerae ExbD1, rather than TolR, to be in agreement with the nomenclature used for the proteins encoded by the upstream genes.…”

Section: Resultsmentioning

confidence: 96%

Vibrio cholerae iron transport: haem transport genes are linked to one of two sets of tonB, exbB, exbD genes

Occhino

Wyckoff

Henderson

et al. 1998

Molecular Microbiology

161

203

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SummaryVibrio cholerae was found to have two sets of genes encoding TonB, ExbB and ExbD proteins. The first set (tonB1, exbB1, exbD1) was obtained by complementation of a V. cholerae tonB mutant. In the mutant, a plasmid containing these genes permitted transport via the known V. cholerae high-affinity iron transport systems, including uptake of haem, vibriobactin and ferrichrome. When chromosomal mutations in exbB1 or exbD1 were introduced into a wild-type V. cholerae background, no defect in iron transport was noted, indicating the existence of additional genes that can complement the defect in the wild-type background. Another region of the V. cholerae chromosome was cloned that encoded a second functional TonB/Exb system (tonB2, exbB2, exbD2 ). A chromosomal mutation in exbB2 also failed to exhibit a defect in iron transport, but a V. cholerae strain that had chromosomal mutations in both the exbB1 and exbB2 genes displayed a mutant phenotype similar to that of an Escherichia coli tonB mutant. The genes encoding TonB1, ExbB1, ExbD1 were part of an operon that included three haem transport genes (hutBCD ), and all six genes appeared to be expressed from a single Fur-regulated promoter upstream of tonB1. A plasmid containing all six genes permitted utilization of haem by an E. coli strain expressing the V. cholerae haem receptor, HutA. Analysis of the hut genes indicated that hutBCD, which are predicted to encode a periplasmic binding protein (HutB) and cytoplasmic membrane permease (HutC and HutD), were required to reconstitute the V. cholerae haem transport system in E. coli. In V. cholerae, the presence of hutBCD stimulated growth when haemin was the iron source, but these genes were not essential for haemin utilization in V. cholerae.

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“…It should be noted that, in Synechocystis 6803, the three clusters that encode putative ExbB-ExbD also show similarity with Escherichia coli TolQTolR (data not shown). Although the TolA-TolQTolR and TonB-ExbB-ExbD energy-coupled import systems show strong sequence homology and mutual functional substitution, no uptake functions for TolA-TolQ-TolR have been described other than for certain bacteriophages and colicins (Braun and Herrmann, 1993).…”

Section: Resultsmentioning

confidence: 99%

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

Jiang

Lou

et al. 2014

The ISME Journal

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Cyanobacteria are globally important primary producers that have an exceptionally large iron requirement for photosynthesis. In many aquatic ecosystems, the levels of dissolved iron are so low and some of the chemical species so unreactive that growth of cyanobacteria is impaired. Pathways of iron uptake through cyanobacterial membranes are now being elucidated, but the molecular details are still largely unknown. Here we report that the non-siderophore-producing cyanobacterium Synechocystis sp. PCC 6803 contains three exbB-exbD gene clusters that are obligatorily required for growth and are involved in iron acquisition. The three exbB-exbDs are redundant, but single and double mutants have reduced rates of iron uptake compared with wild-type cells, and the triple mutant appeared to be lethal. Short-term measurements in chemically well-defined medium show that iron uptake by Synechocystis depends on inorganic iron (Fe 0 ) concentration and ExbB-ExbD complexes are essentially required for the Fe 0 transport process. Although transport of iron bound to a model siderophore, ferrioxamine B, is also reduced in the exbB-exbD mutants, the rate of uptake at similar total [Fe] is about 800-fold slower than Fe 0 , suggesting that hydroxamate siderophore iron uptake may be less ecologically relevant than free iron. These results provide the first evidence that ExbB-ExbD is involved in inorganic iron uptake and is an essential part of the iron acquisition pathway in cyanobacteria. The involvement of an ExbB-ExbD system for inorganic iron uptake may allow cyanobacteria to more tightly maintain iron homeostasis, particularly in variable environments where iron concentrations range from limiting to sufficient.

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Evolutionary relationship of uptake systems for biopolymers in Escherichia coli: cross‐complementation between the TonB‐ExbB‐ExbD and the TolA‐TolQ‐TolR proteins

Cited by 156 publications

References 30 publications

Dimerization of TonB Is Not Essential for Its Binding to the Outer Membrane Siderophore Receptor FhuA of Escherichia coli

Dimerization of TonB Is Not Essential for Its Binding to the Outer Membrane Siderophore Receptor FhuA of Escherichia coli

Vibrio cholerae iron transport: haem transport genes are linked to one of two sets of tonB, exbB, exbD genes

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

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