Disease relevance of tonB

• Evidence is presented for a tonB-dependent illicit transport of the compounds across the outer membrane of E. coli K-12, the process involving jointly and specifically the Fiu and Cir iron-regulated outer membrane proteins [1].
• The genetic context of K. pneumoniae and En. aerogenes tonB is the same, but is different from that of E. coli, Salmonella typhimurium and Serratia marcescens [2].
• This genetic organization has been reported in Haemophilus influenzae, H. ducreyi, Pseudomonas putida and Vibrio cholerae, and may represent a separate lineage of evolution from that of the Enterobacteriaceae in which tonB is unlinked with the accessory genes exbB and exbD [3].
• Nucleotide sequence analysis of DNA fragments subcloned from the Hb-complementing cosmids identified four open reading frames, three of them homologous to Pseudomonas putida, E. coli, and Haemophilus influenzae exbB, exbD, and tonB genes [4].
• The tonB gene of Klebsiella pneumoniae was cloned on a 1.4-kb EcoRV fragment and expressed in Escherichia coli [2].

High impact information on tonB

• The uptake of ferric citrate into the periplasmic space of fecA and tonB mutants via diffusion through the porin channels did not induce transcription of fec transport genes [5].
• DNA sequence of the Escherichia coli tonB gene [6].
• The nucleotide sequence of a cloned section of the Escherichia coli chromosome containing the tonB gene has been determined [6].
• The tonB promoter and terminator resemble other E. coli promoters and terminators; the sequence of the tonB terminator region suggests that it may function bidirectionally [6].
• CCCP inhibited tonB-dependent transport of ferrichrome through FhuADelta5-160 [7].

Chemical compound and disease context of tonB

• The tonB mutant transformed with the heme utilization plasmids could not utilize the siderophore ferrichrome as an iron source, indicating that none of the genes encoded on the heme utilization plasmids complements the tonB defect in E. coli [8].
• The structurally related exbB and tolQ genes are interchangeable in conferring tonB-dependent colicin, bacteriophage, and albomycin sensitivity [9].
• Mutagenic specificity of N-methyl-N'-nitro-N-nitrosoguanidine in the tonB gene on the chromosome of Escherichia coli recA+ and recA- cells [10].
• Hydrogen peroxide-induced microsatellite instability in the Escherichia coli K-12 endogenous tonB gene [11].

Biological context of tonB

• One region is located at 70 min on the E. coli chromosome, upstream of murZ, while the other is at 28 min, downstream of tonB [12].
• This phenotype is partially suppressed by certain mutations in tonB [13].
• The presence of the btuB451 mutation in this fusion gene eliminated all of its tonB-coupled reactions, showing that the TonB box of FepA could be replaced by that from BtuB [13].
• Spectra of ionizing radiation mutagenesis were determined by sequencing X-ray-induced endogenous tonB gene mutations in Escherichia coli polA strains [14].
• However, growth of a FhuADelta5-160 tonB wild-type strain occurred at low ferrichrome concentrations, and ferrichrome was transported at about 45% of the FhuA wild-type rate despite the lack of ferrichrome binding sites provided by the cork [7].

Associations of tonB with chemical compounds

• The tonB mutation with a glutamine to leucine replacement at position 165 was less efficient in restoring the FhuA functions than the glutamine to lysine exchange at the same position [15].
• Mode of action of GR69153, a novel catechol-substituted cephalosporin, and its interaction with the tonB-dependent iron transport system [16].
• Like tonB mutants, exb mutants were resistant to colicin M and albomycin but, in contrast to tonB mutants, showed only reduced sensitivity to colicins B and D. Overexpressed tonB on the multicopy vector pACYC177 largely restored the sensitivity of exb mutants to colicins B, D, and M but only marginally increased sensitivity to albomycin [17].
• N. gonorrhoeae FA1090 utilized ferric enterobactin as the sole iron source when supplied with ferric enterobactin at approximately 10 microM, but growth stimulation was abolished when an omega (Omega) cassette was inserted within fetA or when tonB was insertionally interrupted [18].
• Susceptibility testing with the mutants involved in the iron transport system indicated that the tonB mutant was resistant to BO-1341 [19].

Regulatory relationships of tonB

• Mutations in tonB that suppressed the transport defect phenotype of these btuB mutations were isolated [20].

Other interactions of tonB

• Finally, a strain carrying a mutant fhuA gene on the chromosome in which the linker insertion occurred after amino acid 82 showed a tonB phenotype [21].
• Mutants devoid of all six iron-regulated outer membrane proteins were no more resistant to the probe compounds than fiu cir or tonB strains [1].
• Analysis of the nucleotide sequence in the complementing DNA showed that it codes for three genes in the order of exbB-exbD-tonB [3].
• This suggested involvement of both exbB and tolQ in tonB-dependent uptake [9].
• The various tonB mutations differed markedly in their suppression activities on different btuB or cir mutations [20].

References