Coordination chemistry of microbial iron transport compounds. 16. Isolation, characterization, and formation constants of ferric aerobactin

Harris, Wesley R.; Carrano, Carl J.; Raymond, Kenneth N.

doi:10.1021/ja00504a038

Cited by 161 publications

(134 citation statements)

References 7 publications

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“…In contrast, a net negative charge on ½Fe III H 3 bueaðOHÞ − and cysteine-ligated hemes (37) is likely to contribute to the higher proton affinity of their oxo complexes (19,38). The paramount role of protein ligands and local charges in determining the pK a of metal-bound oxygen is further exemplified by siderophores, where the pK a1 of bound water can shift by as much as 8 pH units (39). Greater variability is expected in the low dielectric environment of a protein.…”

Section: Discussionmentioning

confidence: 99%

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Grzyska

Appelman

Hausinger

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

124

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Iron oxygenases generate elusive transient oxygen species to catalyze substrate oxygenation in a wide range of metabolic processes. Here we resolve the reaction sequence and structures of such intermediates for the archetypal non-heme Fe II and α-ketoglutarate-dependent dioxygenase TauD. Time-resolved Raman spectra of the initial species with 16 O 18 O oxygen unequivocally establish the Fe IV ═O structure. 1 H∕ 2 H substitution reveals direct interaction between the oxo group and the C1 proton of substrate taurine. Two new transient species were resolved following Fe IV ═O; one is assigned to the ν FeO mode of an Fe III ─OðHÞ species, and a second is likely to arise from the vibration of a metal-coordinated oxygenated product, such as Fe II ─O─C 1 or Fe II ─OOCR. These results provide direct insight into the mechanism of substrate oxygenation and suggest an alternative to the hydroxyl radical rebinding paradigm.ferric-oxo | ferryl | non-heme iron | oxygenation | transient Raman I nterest in the mechanism of iron oxygenases arises from their roles in an array of critical biological functions ranging from bacterial biodegradation of xenobiotics and recalcitrant compounds to human drug metabolism and cellular regulation. Many heme and non-heme iron oxygenases are believed to share highly oxidized iron-oxo species as central elements in their reaction mechanisms (1, 2). Several transient oxygen intermediates have been studied extensively in heme enzymes, including compound I-type species of cytochrome P450s (3), but the intermediates occurring during substrate oxygenation have not been directly observed. Even less is known about the transient species in the non-heme Fe oxygenases. An Fe IV -oxo intermediate was observed in the Fe II and α-ketoglutarate-dependent dioxygenase TauD (4-6), the archetype of this enzyme family (7), and in the related prolyl 4-hydroxylase (8) or the chlorinating enzymes CytC3 and SyrB2 (9, 10). The Fe-oxygen vibration in TauD at 821 cm −1 was assigned to an Fe IV ═O stretching mode, whereas an additional oxygen vibration at 583 cm −1 was not assigned (6). Here, through the use of substrate and media isotopes and varying reaction times, we resolve vibrations associated with three distinct transient oxygen-containing species during TauD catalysis that lead us to propose an alternative to the hydroxyl radical rebinding step that is central to the traditionally accepted mechanism (Fig. 1). ResultsTransient Oxygen Species Detected by Difference Raman Spectroscopy. The time dependence of the TauD reaction with 1 H-and 2 H-taurine was examined by cryogenic continuous-flow Raman spectroscopy (Fig. 2 and Fig. S1). The previously reported oxygen vibrations (6) can be seen as shifts at 825∕788 and 578∕555 cm −1 between the 16 O and 18 O derivatives (for 1 H-taurine, Fig. 2A). Intensities of the isotopic shifts diminished rapidly at longer delay times, although the decay of both species was significantly slower and overall intensities were greater with 2 H-taurine.The 16 O∕ 18 O difference spectra aro...

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Section: Discussionmentioning

confidence: 99%

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Grzyska

Appelman

Hausinger

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

124

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“…For the wide variety of siderophores known so far, the corresponding formation constants for iron binding to the fully deprotonated ligand (K f ' ␤ 110 ) ranges over about 30 orders of magnitude. This enormous affinity range is representatively demonstrated by two E. coli siderophores: the mixed citrate-hydroxamate aerobactin as one of the weakest monohexadentatic iron chelators, with a log ␤ 110 of 22.5 (133), and the triscatecholate enterobactin as the strongest iron-chelating compound ever found, displaying a log ␤ 110 of 49 (198). However, since protonation of the donor atoms is a competitive reaction to metal chelation, the pK a values of the donor groups have to be considered in terms of effectiveness of iron complexation.…”

Section: Physicochemical Properties Of Siderophoresmentioning

confidence: 99%

“…In terms of iron binding efficiency, however, the usage of aerobactin as a virulence-related siderophore seems to be less advantageous, since its pFe at physiological pH is about 10 orders of magnitude lower than that of enterobactin and its derivatives. Thus, salmochelin-producing Salmonella strains are capable of exploiting a broad spectrum of host iron sources in all accessible compartments, while for aerobactin-dependent strains, some iron sources are less accessible, such as Fe-transferrin (38), which has a K D for Fe(III) of 10 Ϫ22 M that is comparable to the equivalent value of Fe-aerobactin (6,133) and which furthermore regulates the free serum Fe(III) concentration just below the range of the Fe-aerobactin dissociation constant. Among gram-positive bacteria, many Bacillus species, including nonpathogenic B. subtilis or B. licheniformis as well as pathogenic B. anthracis, B. cereus, and B. thuringiensis, produce the triscatecholate siderophore bacillibactin.…”

Section: Defense and Antidefense: Iron-related Coevolution Of Pathogementioning

confidence: 99%

Siderophore-Based Iron Acquisition and Pathogen Control

Miethke

Marahiel

2007

Microbiol Mol Biol Rev

1,413

1,302

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SUMMARY High-affinity iron acquisition is mediated by siderophore-dependent pathways in the majority of pathogenic and nonpathogenic bacteria and fungi. Considerable progress has been made in characterizing and understanding mechanisms of siderophore synthesis, secretion, iron scavenging, and siderophore-delivered iron uptake and its release. The regulation of siderophore pathways reveals multilayer networks at the transcriptional and posttranscriptional levels. Due to the key role of many siderophores during virulence, coevolution led to sophisticated strategies of siderophore neutralization by mammals and (re)utilization by bacterial pathogens. Surprisingly, hosts also developed essential siderophore-based iron delivery and cell conversion pathways, which are of interest for diagnostic and therapeutic studies. In the last decades, natural and synthetic compounds have gained attention as potential therapeutics for iron-dependent treatment of infections and further diseases. Promising results for pathogen inhibition were obtained with various siderophore-antibiotic conjugates acting as “Trojan horse” toxins and siderophore pathway inhibitors. In this article, general aspects of siderophore-mediated iron acquisition, recent findings regarding iron-related pathogen-host interactions, and current strategies for iron-dependent pathogen control will be reviewed. Further concepts including the inhibition of novel siderophore pathway targets are discussed.

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“…Labelled products were located by autoradiography, and material of R, = 0.53 (Gibson & Magrath, 1969) was eluted in 1 ml distilled water. Aerobactin concentrations were determined from the molar absorption coefficient for ferric aerobactin as reported by Harris et al (1979).…”

Section: Methodsmentioning

confidence: 99%

“…Siderophore concentrations were determined as described above (Harris et al, 1979 Nossal & Heppel (1966). Inner and outer membranes were separated by differential solubility in Triton X-100 (Schnaitman, 1971).…”

Section: Methodsmentioning

confidence: 99%

Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores

Wooldridge

Morrissey²,

Williams³

1992

Journal of General Microbiology

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Purified (14Claerobactin, supplied exogenously to non-growing bacteria, was translocated via the periplasm into the cytoplasm of Escherichia coli K12 strains expressing the aerobactin receptor protein IutA. No significant uptake was observed into either compartment of strains lacking the iutA gene or specifically defective in tonB. Uptake into both compartments was markedly reduced, but not abolished, in an exb mutant. Accumulation of [ 4C]aerobactin in the periplasm offiuD,fiuB orfiuC mutant strains was not significantly lower than in the wildtype strain, but entry into the cytoplasm was greatly reduced in all cases. Uptake of aerobactin by strains wild-type for all transport functions occurred most efficiently in strains either lacking or specifically defective in the genetic determinants for aerobactin biosynthesis; significantly lower levels of exogenous * 4C-labelled siderophore were observed in both Compartments of strains producing aerobactin. Aerobactin-mediated 59Fe uptake, however, was not inhibited by the presence of endogenous aerobactin. Endogenous enterochelin did not affect aerobactin uptake.

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Coordination chemistry of microbial iron transport compounds. 16. Isolation, characterization, and formation constants of ferric aerobactin

Cited by 161 publications

References 7 publications

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Siderophore-Based Iron Acquisition and Pathogen Control

Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores

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Coordination chemistry of microbial iron transport compounds. 16. Isolation, characterization, and formation constants of ferric aerobactin

Cited by 161 publications

References 7 publications

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe IV ═O species

Siderophore-Based Iron Acquisition and Pathogen Control

Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores

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Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species