Non-heme iron enzymes: Contrasts to heme catalysis

Solomon, Edward I.; Decker, Andrea; Lehnert, Nicolai

doi:10.1073/pnas.0336792100

Cited by 221 publications

(195 citation statements)

References 40 publications

(31 reference statements)

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“…Enhancement of F4 may occur via pre-or near-resonance with its 318-nm absorption (4), whereas excitation of FX may be even less favorable implying either a larger energy difference from the electronic transition or a weaker chromophore. Although the Fe II alkoxo complex should not exhibit charge transfer transitions similar to the Fe II -αKG-TauD complex (27), the low symmetry of the Fe II site in TauD may favor spin-forbidden mid-UV transitions below 300 nm, thus allowing for a weak enhancement of oxygen vibrations. In any case, the rapid isotope-dependent disappearance of FX shows that it originates from a transient substrate-derived species.…”

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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“…[40] This model involves initial substrate binding that causes the conversion of the iron center from 6-to 5-coordinate. The enzyme is now ready to coordinate dioxygen and it has been suggested that this allows the enzyme to control reactivity and only implement dioxygenation when sufficient substrate is available.…”

Section: Discussionmentioning

confidence: 99%

Influence of cysteine 164 on active site structure in rat cysteine dioxygenase

et al. 2016

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Cysteine dioxygenase (CDO) is a non-heme mononuclear iron enzyme with unique structural features, namely an intramolecular thioether crosslink between cysteine 93 and tyrosine 157, and a disulfide between substrate L-cysteine and cysteine 164 in the entrance channel to the active site. We investigated how these posttranslational modifications affect catalysis through a kinetic, crystallographic and computational study. The enzyme kinetics of a C164S variant are identical to WT indicating that disulfide formation at C164 does not significantly impair access to the active site at physiological pH. However, at high pH the cysteine-tyrosine crosslink formation is enhanced in C164S. This supports the view that disulfide formation at position 164 can limit access to the active site. The C164S yielded crystal structures of unusual clarity in both resting state and with cysteine bound. Both show that the iron in the cysteine bound complex is a mixture of penta-and hexa-coordinate with a water molecule taking up the final site (60% occupancy), which is where dioxygen is believed to coordinate during turnover. The serine also displays stronger hydrogen bond interactions to a water bound to the amine of the substrate cysteine. However, the interactions between cysteine and iron appear unchanged. DFT calculations support this and show that WT and C164S have similar binding energies for the water molecule in the final site. This variant therefore provides evidence that WT also exists in this equilibrium between penta-and hexa-coordinate forms and presence of the sixth ligand does not strongly affect dioxygen binding.

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“…68,78,[82][83][84][85][86] MCD measures the differential absorption of left and right circular polarised light, similar to circular dichroism (CD), but in the presence of a magnetic field. 84 Application of a magnetic field parallel to the direction of light causes all matter to exhibit MCD activity so it is not restricted to paramagnetic materials.…”

Section: Catalytic Mechanism Of Gpdqmentioning

confidence: 99%

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

et al. 2014

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An enhanced understanding of the metal ion binding and active site structural features of phosphoesterases such as the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ), and the organophosphate degrading agent from Agrobacterium radiobacter (OpdA) have important consequences for potential applications. Coupled with investigations of the metalloenzymes, programs of study to synthesise and characterise model complexes based on these metalloenzymes can add to our understanding of structure and function of the enzymes themselves. This review summarises some of our work and illustrates the significance and contributions of model studies to knowledge in the area.

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Non-heme iron enzymes: Contrasts to heme catalysis

Cited by 221 publications

References 40 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

Influence of cysteine 164 on active site structure in rat cysteine dioxygenase

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

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Non-heme iron enzymes: Contrasts to heme catalysis

Cited by 221 publications

References 40 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

Influence of cysteine 164 on active site structure in rat cysteine dioxygenase

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

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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