Coordination chemistry of microbial iron transport compounds. 19. Stability constants and electrochemical behavior of ferric enterobactin and model complexes

Harris, Wesley R.; Carrano, Carl J.; Cooper, Stephen R.; Sofen, Stephen R.; Avdeef, Alex; McArdle, James V.; Raymond, Kenneth N.

doi:10.1021/ja00514a037

Cited by 294 publications

(261 citation statements)

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“…18,19 The reduction potentials of the salicylate analogs of ferric enterobactin (Table 4) are well within the range of biological reductants and much higher than those typically observed for the corresponding catecholate siderophores. Noteworthy, the reduction potentials observed for the hydroxamate siderophores ferrichrome A and ferrioxamine B are in the same range (Table 4).…”

Section: Reduction Potentials Of Ferric-salicylate Complexesmentioning

confidence: 59%

“…The compounds were titrated only from low to high pH to avoid base-catalyzed hydrolysis of the backbone. 19 In both cases, the intense UV absorption band of the salicylate functionality increases in intensity and shifts to longer wavelengths as the pH is increased to 10 ( Figures 3 and S1). Factor analysis 27 of the titration curves (each data set comprising about 60 spectra and 151 wavelengths for each replicate) indicated for each ligand three sequential protonation equilibria corresponding to logK a values reported in Table 1.…”

Section: Ligand Protonation Constants and Stability Of Ferric Salicylmentioning

confidence: 96%

“…16,17 This result implies the existence of a secondary pathway for intracellular iron release. While ferric enterobactin at neutral pH cannot release iron by reduction, 18,19 protonation of ferric enterobactin makes reduction much easier. 20 Furthermore, low pH binding of ferric enterobactin raises the question of whether a second type of structure might be recognized by proteins involved in ferric enterobactin metabolism.…”

Section: Introductionmentioning

confidence: 99%

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Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹

et al. 2006

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The siderophore enterobactin (Ent) is produced by many species of enteric bacteria to mediate iron uptake. This iron scavenger can be reincorporated by the bacteria as the ferric complex [Fe III (Ent)] 3-and is subsequently hydrolyzed by an esterase to facilitate intracellular iron release. Recent literature reports on altered protein recognition and binding of modified enterobactin increase the significance of understanding the structural features and solution chemistry of ferric enterobactin. The structure of the neutral protonated ferric enterobactin complex [Fe III (H 3 (14) Å 2 ). 1 H NMR spectroscopy was used to monitor the amide bond rotation between the catecholate and salicylate geometries using the gallic complexes of enterobactin; [Ga III (Ent)] 3-and [Ga III (H 3 Ent)] 0 . The ferric salicylate complexes display quasi-reversible reduction potentials from −89 mV to −551 mV (relative to the normal hydrogen electrode NHE) which supports the feasibility of a low pH iron release mechanism facilitated by biological reductants. Keywords

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Section: Reduction Potentials Of Ferric-salicylate Complexesmentioning

confidence: 59%

Section: Ligand Protonation Constants and Stability Of Ferric Salicylmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹

et al. 2006

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“…X-ray crystallography [12][13][14][15] and NMR [9,15,16] have been used for structural characterization. UV [9,14,17,18], IR [8,9,19,20] spectroscopy have been used to probe both the structure of enterobactin as well as the dependence of Fe(III) binding on solution pH. Other methods, such as cyclic voltametry [9,14,15,19] and circular dichroism [14,21,22] were also used for the determination of redox potentials and chirality, respectively.…”

mentioning

confidence: 99%

“…The application of MS analysis to enterobactin is complicated by the enterobactin molecule's susceptibility to degradation. This degradation is caused by the presence of ester linkages in the enterobactin structure, subjecting the molecule to acid and base-catalyzed hydrolysis reactions in solution [19,34]. Additionally, Raymond et al [20] observed a pH dependence of the binding of Fe(III) to enterobactin.…”

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Infrared multiphoton dissociation of the siderophore enterobactin and its Fe(III) complex. Influence of Fe(III) binding on dissociation kinetics and relative energetics

Leslie

Daneshfar

Volmer

2007

J. Am. Soc. Mass Spectrom.

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The dissociation pathways of the siderophore enterobactin and its complex with Fe(III) were examined using infrared multiphoton dissociation (IRMPD). Under experimental conditions (pH ϭ 3.5), both compounds' electrospray spectra exhibited exclusively singly-charged anions. The compositions of the dissociation products were characterized by accurate mass measurements using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The primary dissociation channel for both species was determined to be the loss of one serine group from the precursor molecules. To further investigate the influence of Fe(III) binding on the intramolecular interactions, dissociation kinetics and relative energetics for the loss of this serine group were determined using the focused radiation for gaseous multiphoton energytransfer (FRAGMENT) method. From the kinetic data, it was found that enterobactin was ϳseven times more reactive than its Fe(III) complex over the range of laser intensities investigated. The relative activation energies, however, exhibited similar values, ϳ7 kcal · mol Ϫ1 . These results suggest that at pH ϭ 3.5, Fe(III) interacts with only two of the three serine groups. The results from the present work are believed to be valuable for the characterization of novel siderophores as well as their associated metabolites and synthetic analogues. (J Am Soc Mass Spectrom 2007, 18, 632-641)

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Iron Transport: Siderophores

Matzanke

2005

Encyclopedia of Inorganic Chemistry

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Siderophores (from the Greek: iron carrier) are low molecular mass (500–1500 Da) iron chelators that are synthesized in bacteria and fungi under conditions of iron deficiency. Siderophores exhibit extraordinarily high complex formation constants for ferric iron with β‐values ranging from 10 20 to approximately 10 50 . Fe 2+ ‐siderophores are some 20 orders of magnitude less stable than their Fe 3+ counterparts. The d5 electronic configuration of Fe 3+ rules out any crystal field stabilization energy and makes ferric iron complexes relatively labile with respect to isomerization and ligand exchange. Siderophores display a selectivity for iron that is reflected in the corresponding complex stability constants that are higher with Fe 3+ than with Al 3+ , or with bivalent cations like Ca 2+ , Cu 2+ or Zn 2+ . Microorganisms excrete desferrisiderophores in order to scavenge iron from the environment. The competition for iron by siderophores, the mechanisms of siderophore uptake through microbial membranes, and the intracellular pathways of siderophore‐iron utilization strongly depend on thermodynamic, kinetic, and structural features of the ferric iron siderophore complexes. The structural features of siderophores are diverse. The ligating groups contain oxygen atoms of hydroxamate, catecholate, α‐hydroxy carboxylic and salicylic acids, or oxazoline and thiazoline nitrogen. Reduction potentials of ferric siderophore complexes vary between −700 and −150 mV. In particular at the low potential end below −450 mV, special biological strategies of reductive iron removal are required because these potentials are too negative for typical cellular reductases. The coordination and redox chemistry of siderophores is also reflected in the mechanisms of siderophore‐mediated iron uptake in microorganisms. A classic example is the intracellular removal of iron from enterobactin. The permeation of cell walls or bacterial membranes by siderophores is in most microbes a highly specific process requiring an array of up to eight proteins. The advent of modern molecular biology delivered a cornucopia of methods enabling high‐yield production of specific gene products relevant to siderophore synthesis and transport, analyses of structure‐function relationships (employing site directed mutagenesis), and detailed insights into the regulation of the corresponding processes. One siderophore, ferrioxamine B, serves as a detoxifier in iron overload diseases and in the treatment of β‐thalassemia. Siderophores and siderophore analogs also play a role in MRI and are employed as basic models for actinide chelators in order to remove these metals from the environment or from a contaminated body.

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Coordination chemistry of microbial iron transport compounds. 19. Stability constants and electrochemical behavior of ferric enterobactin and model complexes

Cited by 294 publications

References 9 publications

Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹

Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹

Infrared multiphoton dissociation of the siderophore enterobactin and its Fe(III) complex. Influence of Fe(III) binding on dissociation kinetics and relative energetics

Iron Transport: Siderophores

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Coordination chemistry of microbial iron transport compounds. 19. Stability constants and electrochemical behavior of ferric enterobactin and model complexes

Cited by 294 publications

References 9 publications

Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin1

Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin1

Infrared multiphoton dissociation of the siderophore enterobactin and its Fe(III) complex. Influence of Fe(III) binding on dissociation kinetics and relative energetics

Iron Transport: Siderophores

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Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹

Enterobactin Protonation and Iron Release: Structural Characterization of the Salicylate Coordination Shift in Ferric Enterobactin¹