Functional models for catechol dioxygenases: Iron(III) complexes of cis-facially coordinating linear 3N ligands

Velusamy, Marappan; Mayilmurugan, Ramasamy; Palaniandavar, Mallayan

doi:10.1016/j.jinorgbio.2005.01.008

Cited by 45 publications

(112 citation statements)

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“…[44] Also several works were published on functional mimics of both intradiol and extradiol-cleaving enzymes. [45][46][47] These structure-function studies highlight the great plasticity of the enzyme active site and make these enzymes particularly promising for protein-engineering studies that aim both at a more precise characterisation of the catalytic properties and at reshaping for technological applicative purposes. To date, to our knowledge, no protein-engineering approach has been performed on catechol 1,2-dioxygenases.…”

Section: Discussionmentioning

confidence: 99%

Fine‐Tuning of Catalytic Properties of Catechol 1,2‐Dioxygenase by Active Site Tailoring

Caglio

Valetti

Caposio³

et al. 2009

ChemBioChem

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Catechol 1,2-dioxygenases and chlorocatechol dioxygenases are Fe(III)-dependent enzymes that do not require a reductant to perform the ortho cleavage of the aromatic ring. The reaction mechanism is common to the two enzymes, and active-site residues must play a key role in the fine-tuning of specificity. Protein engineering was applied for the first time to the catalytic pocket of a catechol 1,2-dioxygenase by site-specific and site-saturation mutagenesis with the purpose of redesigning the pocket shape for improved catalysis on bulky derivatives. Mutants were analysed for changes in kinetic parameters: variants for residue 69 show an inversion of specificity with a preference towards 4-chlorocatechol (decrease of K(M) by a factor of 20) and activity on the rarely recognised substrate 4,5-dichlorocatechol, thus creating a novel, engineered chlorocatechol dioxygenase. A L69A substitution conveys gain-of-function activity towards 4-tert-butylcatechol. Mutations of position 72 enhance k(cat) towards chlorinated substrates. The biphasic Arrhenius plot observed in A72S suggests the involvement of a dynamic switch in the fine regulation of the enzyme.

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Section: Discussionmentioning

confidence: 99%

Fine‐Tuning of Catalytic Properties of Catechol 1,2‐Dioxygenase by Active Site Tailoring

Caglio

Valetti

Caposio³

et al. 2009

ChemBioChem

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“…The most active and studied systems are those containing the 2,6-bis(arylimino)-pyridyl moiety (NNN ligands), [1] although examples with ONN [2] and PNP [3] ligands have also been reported. Recently, cobalt complexes containing tridentate ligands have also been combined with iron to create mixed-valence and heterometallic [2 ϫ 2] grid-like arrays, [4] spin-crossover complexes, [5] models of enzyme active sites such as catechol dioxygenases [6] and nitrile hydratase, [7] and asymmetric sulfide oxidation catalysts. [8] Some of us have been involved in the study of the coordinating behaviour of asymmetric tridentate ligands towards transition metals for several years.…”

Section: Introductionmentioning

confidence: 99%

A Ligand‐Driven Geometry Switch in Octahedral and Trigonal‐Bipyramidal Iron Complexes Containing (H)PNO and PNN Ligands

et al. 2006

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Complexation reactions of FeII and FeIII salts with the tridentate ligands 2‐(diphenylphosphanyl)benzaldehyde benzoylhydrazone [(H)PNO] and N‐[2‐(diphenylphosphanyl)benzylidene]‐2‐(2‐pyridyl)ethanamine (PNN) was carried out. For (H)PNO, reaction of a stoichiometric amount of anhydrous FeCl2 in the presence of a primary alcohol such as MeOH, EtOH or nBuOH gave the mixed‐valence FeII/FeIII paramagnetic complex [Fe{κ3‐(H)PNO}2]Cl[FeCl4], whereas the reaction between FeCl2 and a twofold excess of (H)PNO in the presence of AgOTf (OTf = triflate, OSO2CF3) led to the isolation of the bis‐chelate paramagnetic ferrous complex [Fe{κ3‐(H)PNO}2][OTf]2. A diamagnetic bis‐chelate ferrous complex [Fe{κ3‐(PNO)2}] was instead obtained from the reaction of FeCl2 with a twofold excess of (H)PNO in the presence of NaOMe. In the case of the PNN ligand, the 1:1 reaction with FeCl2 gave the neutral paramagnetic trigonal‐bipyramidal complex [Fe(κ3‐PNN)Cl2]. The X‐ray structures of [Fe{κ3‐(H)PNO}2]Cl[FeCl4], [Fe2{κ3‐(H)PNO}2Cl6] and [Fe(κ3‐PNN)Cl2] are reported, together with CV and magnetic susceptibility measurements and an ab initio study aimed at rationalizing the different stoichiometries and structures observed with the two tridentate ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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“…But it is interesting that no deviation from a planar aromatic ring is observed for the anaerobic complex of 2,3-HPCD with substrate. Even though intradiol dioxygenases and their models [23][24][25][26][27][28][29][30][31][32][33] have been more extensively studied and thus more understood, extradiol dioxygenase enzymes have not been studied in detail in spite of the latter constituting the more common iron enzymes for the biodegradation of aromatic molecules in the soil. The difficulty in studying extradiol dioxygenases could be attributed to lack of spectroscopic probes available for iron(II) and oxygen activation mechanism has been proposed 34 for the extradiol cleavage.…”

Section: Introductionmentioning

confidence: 99%

“…51,52 In contrast, on replacing the pyridine backbone in L2 as in L4 which coordinates to iron(III) center in facial fashion due to the sp 3 hybridization of amine N-atom. 27 Upon adding catecholate dianions to 1-4 in DMF two absorption features appear in the visible region (435-620 and 610-800 nm), 27,45 which are assigned to the catecholate-to-iron(III) charge-transfer transitions involving two different catecholate orbitals. [25][26][27][53][54][55] The energies of both the bands are shifted to higher region as the substituents on the catecholate ring are varied from electron-donating to electron-withdrawing (figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, on replacing the pyridine backbone in 3 as in 4, the LMCT band is shifted to lower energy due to the weak binding of amine N-atom, which may increase the Lewis acidity and hence the reactivity. 27 Thus the spectral studies reveal the importance of electronic factors of the tridentate ligands in tuning the Lewis acidity of the iron(III) center and hence the reactivity (cf. below).…”

Section: Introductionmentioning

confidence: 99%

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Mononuclear non-heme iron(III) complexes of linear and tripodal tridentate ligands as functional models for catechol dioxygenases: Effect of N-alkyl substitution on regioselectivity and reaction rate

Palaniandavar

Visvaganesan

2011

J Chem Sci

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Catechol dioxygenases are responsible for the last step in the biodegradation of aromatic molecules in the environment. The iron(II) active site in the extradiol-cleaving enzymes cleaves the C-C bond adjacent to the hydroxyl group, while the iron(III) active site in the intradiol-cleaving enzymes cleaves the C-C bond in between two hydroxyl groups. A series of mononuclear iron(III) complexes of the type [Fe(L)Cl 3 ], where L is the linear N -alkyl substituted bis(pyrid-2-ylmethyl)amine, N -alkyl substituted N -(pyrid-2-ylmethyl)ethylenediamine, linear tridentate 3N ligands containing imidazolyl moieties and tripodal ligands containing pyrazolyl moieties have been isolated and studied as structural and functional models for catechol dioxygenase enzymes. All the complexes catalyse the cleavage of catechols using molecular oxygen to afford both intra-and extradiol cleavage products. The rate of oxygenation depends on the solvent and the Lewis acidity of iron(III) center as modified by the sterically demanding N -alkyl groups. Also, our studies reveal that stereo-electronic factors like the Lewis acidity of the iron(III) center and the steric demand of ligands, as regulated by the N -alkyl substituents, determine the regioselectivity and the rate of dioxygenation. In sharp contrast to all these complexes, the pyrazole-containing tripodal ligand complexes yield mainly the oxidized product benzoquinone.

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Functional models for catechol dioxygenases: Iron(III) complexes of cis-facially coordinating linear 3N ligands

Cited by 45 publications

References 41 publications

Fine‐Tuning of Catalytic Properties of Catechol 1,2‐Dioxygenase by Active Site Tailoring

Fine‐Tuning of Catalytic Properties of Catechol 1,2‐Dioxygenase by Active Site Tailoring

A Ligand‐Driven Geometry Switch in Octahedral and Trigonal‐Bipyramidal Iron Complexes Containing (H)PNO and PNN Ligands

Mononuclear non-heme iron(III) complexes of linear and tripodal tridentate ligands as functional models for catechol dioxygenases: Effect of N-alkyl substitution on regioselectivity and reaction rate

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