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Sulfate as a synergistic anion facilitating iron binding by the bacterial transferrin FbpA: the origins and effects of anion promiscuity.

ABSTRACT: The ferric binding protein, FbpA, has been demonstrated to facilitate the transport of naked Fe3+ across the periplasmic space of several Gram-negative bacteria. The sequestration of iron by FbpA is facilitated by the presence of a synergistic anion, such as phosphate or sulfate. Here we report the sequestration of Fe3+ by FbpA in the presence of sulfate, at an assumed periplasmic pH of 6.5 to form FeFbpA-SO4 with K'(eff) = 1.7 x 10(16) M(-1) (at 20 degrees C, 50 mM MES, 200 mM KCl). The iron affinity of the FeFbpA-SO4 protein assembly is 2 orders of magnitude lower than when bound with phosphate and is the lowest of any of the FeFbpA-X assemblies yet reported. Iron reduction at the cytosolic membrane receptor may be an essential aspect of the periplasmic iron-transport process, and with an E(1/2) of -158 mV (NHE), FeFbpA-SO4 is the most easily reduced of all FeFbpA-X assemblies yet studied. The variation of FeFbpA-X assembly stability (K'(eff)) and ease of reduction (E(1/2)) with differing synergistic anions X(n-) are correlated over a range of 14 kJ, suggesting that the variations in redox potentials are due to stabilization of Fe3+ in FeFbpA-X by X(n-). Anion promiscuity of FbpA in the diverse composition of the periplasmic space is illustrated by the ex vivo exchange kinetics of FeFbpA-SO4 with phosphate and arsenate, where first-order kinetics with respect to FeFbpA-SO4 (k = 30 s(-1)) are observed at pH 6.5, independent of entering anion concentration and identity. Anion lability and influence on the iron affinity and reduction potential for FeFbpA-X support the hypothesis that synergistic anion exchange may be an important regulator in iron delivery to the cytosol. This structural and thermodynamic analysis of anion binding in FeFbpA-X provides additional insight into anion promiscuity and importance.

SUBMITTER: Heymann JJ

PROVIDER: S-EPMC3674819 | biostudies-literature | 2007 Aug

REPOSITORIES: biostudies-literature

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Sulfate as a synergistic anion facilitating iron binding by the bacterial transferrin FbpA: the origins and effects of anion promiscuity.

Heymann J J JJ Weaver K D KD Mietzner T A TA Crumbliss A L AL

Journal of the American Chemical Society 20070714 31

The ferric binding protein, FbpA, has been demonstrated to facilitate the transport of naked Fe3+ across the periplasmic space of several Gram-negative bacteria. The sequestration of iron by FbpA is facilitated by the presence of a synergistic anion, such as phosphate or sulfate. Here we report the sequestration of Fe3+ by FbpA in the presence of sulfate, at an assumed periplasmic pH of 6.5 to form FeFbpA-SO4 with K'(eff) = 1.7 x 10(16) M(-1) (at 20 degrees C, 50 mM MES, 200 mM KCl). The iron af ...[more]

PMID: 17630737

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Project description:Moraxella catarrhalis is a Gram-negative bacterium that is responsible for a substantial proportion of upper respiratory infections in children and lower respiratory infections in the elderly. Moraxella catarrhalis resides exclusively on the mucosal surfaces of the upper respiratory tract of humans and is capable of directly acquiring iron for growth from the host glycoproteins human transferrin (hTf) and human lactoferrin (hLf). The iron-bound form of these glycoproteins is initially captured by the surface lipoproteins Tf or Lf binding protein B (TbpB or LbpB) and delivered to the integral outer membrane TonB-dependent transport (TBDT) proteins, Tf binding protein A (TbpA) or Lf binding protein A (LbpA). The extraction of iron involves conformational changes in Lf and Tf to facilitate iron removal followed by its transport across the outer membrane by a well characterized process for TBDTs. Surprisingly the disruption of the gene encoding another TBDT, CopB, results in a reduction in the ability to grow on human Tf or Lf. The possibility that this could have been due to an artifact of mutant construction that resulted in the inhibition of TonB-mediated process was eliminated by a complete deletion of the CopB gene. A systematic evaluation of the impact on growth under various conditions by deletions of the genes encoding TbpA, LbpA, and CopB as well as mutations of the iron liganding residues and TonB box region of CopB was implemented. The results indicate that although CopB is capable of effectively acquiring iron from the growth medium, it does not directly acquire iron from Tf or Lf. We propose that the indirect effect on iron transport from Tf and Lf by CopB could possibly be explained by the association of TBDTs at gaps in the peptidoglycan layer that may enhance the efficiency of the process. This concept is supported by previous studies demonstrating an indirect effect on growth of Tf and Lf by deletion of the peptidoglycan binding outer membrane lipoprotein RmpM in Neisseria that also reduced the formation of larger complexes of TBDTs.

Project description:Background:Iron deficiency anemia (IDA) is a widespread nutritional deficiency, and iron supplementation, especially with ferrous sulfate (FeSO4), is the most common strategy to treat IDA; however, compliance is often poor with daily FeSO4 owing to negative side effects. In a previous study, iron from iron-enriched Aspergillus oryzae [Ultimine® Koji Iron (ULT)] was absorbed similarly to FeSO4. Objectives:The main objective of this study was to assess the safety of consuming ULT in terms of increasing non-transferrin-bound iron (NTBI) and gastrointestinal distress. Methods:Young female participants (n = 16) with serum ferritin <40 ?g/L were randomly assigned to a double-blind, 9-wk crossover study with a 3-wk placebo/washout period between treatments. Oral FeSO 4 and ULT supplements containing 65 mg Fe were administered daily for 21 consecutive days. On day 1, serum iron (SI), percentage transferrin saturation (%TS), and NTBI were measured for 8 h on the first day of iron consumption. Changes in biochemical indicators were evaluated after 3 wk consumption. Side effects questionnaires were completed weekly on 2 randomly selected weekdays and 1 weekend day for the entire study. Results:SI, %TS, and NTBI were all markedly higher during hours 2-8 (P < 0.001) with FeSO4 than with ULT. Oxidative stress, inflammatory, and kidney and liver function markers remained unchanged with both supplementations compared with placebo. Changes in iron status markers were not significantly different among the 3 treatments. Individual or global side effects were not significantly different among all treatments. Even when common side effects of nausea, constipation, and diarrhea were combined, FeSO4 treatment had a significantly higher effect than ULT (P = 0.04) and placebo (P = 0.004) only at week 3, but the difference was not significant between ULT and placebo. Conclusions:Low NTBI production and fewer common gastrointestinal side effects with ULT suggest that it is a safe oral iron supplement to treat IDA. This trial was registered at clinicaltrials.gov as NCT04018300.

Dataset Information

Sulfate as a synergistic anion facilitating iron binding by the bacterial transferrin FbpA: the origins and effects of anion promiscuity.

Publications

Sulfate as a synergistic anion facilitating iron binding by the bacterial transferrin FbpA: the origins and effects of anion promiscuity.

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