Ferrioxamine-mediated Iron(III) utilization by Salmonella enterica.
(9/2363)
Utilization of ferrioxamines as sole sources of iron distinguishes Salmonella enterica serotypes Typhimurium and Enteritidis from a number of related species, including Escherichia coli. Ferrioxamine supplements have therefore been used in preenrichment and selection media to increase the bacterial growth rate while selectivity is maintained. We characterized the determinants involved in utilization of ferrioxamines B, E, and G by S. enterica serotype Typhimurium by performing siderophore cross-feeding bioassays. Transport of all three ferric siderophores across the outer membrane was dependent on the FoxA receptor encoded by the Fur-repressible foxA gene. However, only the transport of ferrioxamine G was dependent on the energy-transducing protein TonB, since growth stimulation of a tonB strain by ferrioxamines B and E was observed, albeit at lower efficiencies than in the parental strain. Transport across the inner membrane was dependent on the periplasmic binding protein-dependent ABC transporter complex comprising FhuBCD, as has been reported for other hydroxamate siderophores of enteric bacteria. The distribution of the foxA gene in the genus Salmonella, as indicated by DNA hybridization studies and correlated with the ability to utilize ferrioxamine E, was restricted to subspecies I, II, and IIIb, and this gene was absent from subspecies IIIa, IV, VI, and VII (formerly subspecies IV) and Salmonella bongori (formerly subspecies V). S. enterica serotype Typhimurium mutants with either a transposon insertion or a defined nonpolar frameshift (+2) mutation in the foxA gene were not able to utilize any of the three ferrioxamines tested. A strain carrying the nonpolar foxA mutation exhibited a significantly reduced ability to colonize rabbit ileal loops compared to the foxA+ parent. In addition, a foxA mutant was markedly attenuated in mice inoculated by either the intragastric or intravenous route. Mice inoculated with the foxA mutant were protected against subsequent challenge by the foxA+ parent strain. (+info)
Alternative structural state of transferrin. The crystallographic analysis of iron-loaded but domain-opened ovotransferrin N-lobe.
(10/2363)
Transferrins bind Fe3+ very tightly in a closed interdomain cleft by the coordination of four protein ligands (Asp60, Tyr92, Tyr191, and His250 in ovotransferrin N-lobe) and of a synergistic anion, physiologically bidentate CO32-. Upon Fe3+ uptake, transferrins undergo a large scale conformational transition: the apo structure with an opening of the interdomain cleft is transformed into the closed holo structure, implying initial Fe3+ binding in the open form. To solve the Fe3+-loaded, domain-opened structure, an ovotransferrin N-lobe crystal that had been grown as the apo form was soaked with Fe3+-nitrilotriacetate, and its structure was solved at 2.1 A resolution. The Fe3+-soaked form showed almost exactly the same overall open structure as the iron-free apo form. The electron density map unequivocally proved the presence of an iron atom with the coordination by the two protein ligands of Tyr92-OH and Tyr191-OH. Other Fe3+ coordination sites are occupied by a nitrilotriacetate anion, which is stabilized through the hydrogen bonds with the peptide NH groups of Ser122, Ala123, and Gly124 and a side chain group of Thr117. There is, however, no clear interaction between the nitrilotriacetate anion and the synergistic anion binding site, Arg121. (+info)
Iron-induced cytotoxicity in cultured rat retinal neurons.
(11/2363)
Oxidative stress has been proposed as a major injury mechanism in the central nervous system including the retina. In this study, as an initial attempt to study the mechanism of oxidative injury in the retina, we developed a cell culture model by utilizing the iron exposure paradigm. Exposure of rat retinal cultures for 24 hours to 10-40 MicroM ferrous or ferric chloride induced a concentration-dependent death of retinal neurons but not of photoreceptors or astrocytes. An antioxidant, trolox effectively attenuated the iron-induced death of neurons and photoreceptors in a dose-dependent manner whereas neither glutamate receptor antagonists nor cycloheximide were protective. Of retinal interneurons, GABAergic neurons were more vulnerable to the iron toxicity than calbindin (+) horizontal neurons. These findings show that iron exposure induces anti-oxidant-sensitive neuronal injury in retinal culture, independent of the excitotoxic or the apoptotic mechanisms. Of retinal neurons, different cell types exhibit differential vulnerabilities to the iron-induced oxidative injury. This simplified culture model system may be useful in elucidating mechanisms of oxidative injury in the retina. (+info)
The haemin storage (Hms+) phenotype of Yersinia pestis is not essential for the pathogenesis of bubonic plague in mammals.
(12/2363)
The haemin storage (Hms+) phenotype of Yersinia pestis enables this bacillus to form greenish/brown or red colonies on haemin or Congo Red agar plates, respectively, at 26 but not 37 degrees C. Escherichia coli strains that contain mutations in genes essential for siderophore biosynthesis, porphyrin generation and/or haemin transport remain unable to utilize exogenous haemin as a nutritional iron or porphyrin source when transformed with the cloned Y. pestis hmsHFRS locus. Further physiological analysis of the Hms+ phenotype of Y. pestis strain KIM6+ suggests that the haemin and inorganic iron stored by the Hms system was not used nutritionally under subsequent iron-deficient conditions. In vitro analysis of the bactericidal effects of hydrogen peroxide, superoxide and nitric oxide showed that Hms- Y. pestis cells, in certain cases, were more susceptible than the Hms+ parent cells to these reactive oxygen species at 26 and/or 37 degrees C. In adherence assays, a higher percentage of Hms+ cells were associated with HeLa cells and normal human neutrophils, compared to Hms- cells. However, the Hms+ phenotype did not provide any additional protection against the killing effects of neutrophils. Finally, LD50 analysis in subcutaneously infected mice showed that an Hms- strain was slightly more virulent than Hms+, indicating that the Hms phenotype is not essential for the pathogenesis of bubonic plague in mammals. (+info)
Ferric enterobactin binding and utilization by Neisseria gonorrhoeae.
(13/2363)
FetA, formerly designated FrpB, an iron-regulated, 76-kDa neisserial outer membrane protein, shows sequence homology to the TonB-dependent family of receptors that transport iron into gram-negative bacteria. Although FetA is commonly expressed by most neisserial strains and is a potential vaccine candidate for both Neisseria gonorrhoeae and Neisseria meningitidis, its function in cell physiology was previously undefined. We now report that FetA functions as an enterobactin receptor. 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. FA1090 FetA specifically bound 59Fe-enterobactin, with a Kd of approximately 5 microM. Monoclonal antibodies raised against the Escherichia coli enterobactin receptor, FepA, recognized FetA in Western blots, and amino acid sequence comparisons revealed that residues previously implicated in ferric enterobactin binding by FepA were partially conserved in FetA. An open reading frame downstream of fetA, designated fetB, predicted a protein with sequence similarity to the family of periplasmic binding proteins necessary for transporting siderophores through the periplasmic space of gram-negative bacteria. An Omega insertion within fetB abolished ferric enterobactin utilization without causing a loss of ferric enterobactin binding. These data show that FetA is a functional homolog of FepA that binds ferric enterobactin and may be part of a system responsible for transporting the siderophore into the cell. (+info)
Nordihydroguairetic acid is a potent inhibitor of ferric-nitrilotriacetate-mediated hepatic and renal toxicity, and renal tumour promotion, in mice.
(14/2363)
Ferric-nitrilotriacetate (Fe-NTA) is a known renal carcinogen. In the present study, we report the effect of a potent lignin-derived herbal antioxidant, nordihydroguairetic acid (NDGA), against Fe-NTA-mediated tissue toxicity. Fe-NTA (alone) treatment of mice enhances ornithine decarboxylase activity to 259% in liver and 341% in kidney and increases [3H]thymidine incorporation in DNA to 250% in liver and 324% in kidney compared with the corresponding saline-treated controls. The enhanced ornithine decarboxylase activity and DNA synthesis showed a reduction to 138 and 123%, respectively, in liver at a higher dose of 2 mg NDGA/day/animal whereas in kidney the reduction was to 118 and 102%, respectively, compared with the corresponding saline-treated controls. In the Fe-NTA (alone)-treated group, a 12% renal tumour incidence was recorded whereas, in N-diethylnitrosamine (DEN)-initiated and Fe-NTA-promoted animals, the percentage tumour incidence was increased to 68% as compared with untreated controls. No tumour incidence was recorded in the DEN-initiated, non-promoted group. The administration of NDGA, afforded >80% protection against DEN- and Fe-NTA-mediated renal tissue injury in vivo. Fe-NTA treatment also enhanced hepatic and renal microsomal lipid peroxidation to 170 and 205% of saline-treated controls, respectively, and hydrogen peroxide generation by >2.5-fold in both tissues accompanied by a 51 and 21% decrease in the level of glutathione and 35-48 and 35-50% decrease in the activities of glutathione-metabolizing and antioxidant enzymes in liver and kidney, respectively. These changes were reversed significantly in animals receiving a pre-treatment of NDGA. Our data show that NDGA can abrogate the toxic and tumour-promoting effects of Fe-NTA in liver and kidney of mice and can serve as a potent chemopreventive agent to suppress oxidant-induced tissue injury and tumorigenesis. (+info)
Manipulating the coordination mumber of the ferric iron within the cambialistic superoxide dismutase of Propionibacterium shermanii by changing the pH-value A crystallographic analysis.
(15/2363)
The structure of the Propionibacterium freudenreichii subspecies shermanii superoxide dismutase (SOD) was determined at various pH values. As a comparison, the structure of the fluoride coordinated SOD was solved. The SOD crystallizes at pH 6.1 in the space group C2221 with two subunits, A and B, in the asymmetric unit. An increase of the pH value changes the cell parameters slightly but not the symmetry of the crystals. The overall structure of the SOD remains a compact tetrameter and is comparable to that at pH 6.1 no matter whether the pH increases or fluoride is added. At values above pH 7.4, an additional hydroxide ion can bind to the active center. Its position is similar to the binding site of the fluoride. The coordination number changes from five to six if the pH increases or fluoride is added. The binding behavior of the hydroxide ion is different for subunit A and B. Structures at different pH-values are comparable with models derived by spectroscopic methods. The influence of temperature on the binding properties of the hydroxide ion was investigated using analysis of an X-ray structure solved at pH 8.1 and 140 K. Compared to the structure at room temperature, the structural changes are observable but remain small. The consequences of hydroxide binding to the iron are discussed. (+info)
Nitric oxide and iron proteins.
(16/2363)
Nitric oxide interactions with iron are the most important biological reactions in which NO participates. Reversible binding to ferrous haem iron is responsible for the observed activation of guanylate cyclase and inhibition of cytochrome oxidase. Unlike carbon monoxide or oxygen, NO can also bind reversibly to ferric iron. The latter reaction is responsible for the inhibition of catalase by NO. NO reacts with the oxygen adduct of ferrous haem proteins (e.g. oxyhaemoglobin) to generate nitrate and ferric haem; this reaction is responsible for the majority of NO metabolism in the vasculature. NO can also interact with iron-sulphur enzymes (e.g. aconitase, NADH dehydrogenase). This review describes the underlying kinetics, thermodynamics, mechanisms and biological role of the interactions of NO with iron species (protein and non-protein bound). The possible significance of iron reactions with reactive NO metabolites, in particular peroxynitrite and nitroxyl anion, is also discussed. (+info)