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Calorimetric assessment of Fe(2+) binding to ?-ketoglutarate/taurine dioxygenase: ironing out the energetics of metal coordination by the 2-His-1-carboxylate facial triad.

ABSTRACT: The thermodynamic properties of Fe(2+) binding to the 2-His-1-carboxylate facial triad in ?-ketoglutarate/taurine dioxygenase (TauD) were explored using isothermal titration calorimetry. Direct titrations of Fe(2+) into TauD and chelation experiments involving the titration of ethylenediaminetetraacetic acid into Fe(2+)-TauD were performed under an anaerobic environment to yield a binding equilibrium of 2.4 (±0.1) × 10(7) (Kd = 43 nM) and a ?G° value of -10.1 (±0.03) kcal/mol. Further analysis of the enthalpy/entropy contributions indicates a highly enthalpic binding event, where ?H = -11.6 (±0.3) kcal/mol. Investigations into the unfavorable entropy term led to the observation of water molecules becoming organized within the Fe(2+)-TauD structure.

SUBMITTER: Henderson KL

PROVIDER: S-EPMC5453723 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Calorimetric assessment of Fe(2+) binding to α-ketoglutarate/taurine dioxygenase: ironing out the energetics of metal coordination by the 2-His-1-carboxylate facial triad.

Henderson Kate L KL Müller Tina A TA Hausinger Robert P RP Emerson Joseph P JP

Inorganic chemistry 20150210 5

The thermodynamic properties of Fe(2+) binding to the 2-His-1-carboxylate facial triad in α-ketoglutarate/taurine dioxygenase (TauD) were explored using isothermal titration calorimetry. Direct titrations of Fe(2+) into TauD and chelation experiments involving the titration of ethylenediaminetetraacetic acid into Fe(2+)-TauD were performed under an anaerobic environment to yield a binding equilibrium of 2.4 (±0.1) × 10(7) (Kd = 43 nM) and a ΔG° value of -10.1 (±0.03) kcal/mol. Further analysis o ...[more]

PMID: 25668068

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The Irving-Williams series and the 2-His-1-carboxylate facial triad: a thermodynamic study of Mn2+, Fe2+, and Co2+ binding to taurine/?-ketoglutarate dioxygenase (TauD).

Project description:Taurine/?-ketoglutarate (?KG) dioxygenase (TauD) is an E. coli nonheme Fe2+- and ?KG-dependent metalloenzyme that catalyzes the hydroxylation of taurine, leading to the production of sulfite. The metal-dependent active site in TauD is formed by two histidine and one aspartate that coordinating to one face of an octahedral coordination geometry, known as the 2-His-1-carboxylate facial triad. This motif is found in many nonheme Fe2+ proteins, but there is limited information on the thermodynamic parameters that govern metal-ion binding to this site. Here, we report data from calorimetry and related biophysical techniques to generate complete thermodynamic profiles of Mn2+ and Co2+ binding to TauD, and these values are compared to the Fe2+ data reported earlier Henderson et al. (Inorg Chem 54: 2278-2283, 2015). The buffer-independent binding constants (K) were measured to be 1.6?×?106, 2.4?×?107, and 1.7?×?109, for Mn2+, Fe2+, and Co2+, respectively. The corresponding ?G° values were calculated to be - 8.4, - 10.1, and - 12.5 kcal/mol, respectively. The metal-binding enthalpy changes (?H) for these binding events are - 11.1 (±?0.1), - 12.2 (±?0.1), and - 16.0 (±?0.6) kcal/mol, respectively. These data are fully consistent with the Irving-Williams series, which show an increasing affinity for transition metal ions across the periodic table. It appears that the periodic increase in affinity, however, is a result of a complicated summation of enthalpy terms (including favorable metal-ion coordination processes and unfavorable ionization events) and related entropy terms.

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| S-EPMC7642179 | biostudies-literature

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| S-EPMC3931003 | biostudies-literature

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