Model of the MitoNEET [2Fe−2S] Cluster Shows Proton Coupled Electron Transfer

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• 作者：Marie Bergner ; Sebastian Dechert ; Serhiy Demeshko ; Claudia Kupper ; James M. Mayer ; Franc Meyer
• 刊名：Journal of the American Chemical Society
• 出版年：2017
• 出版时间：January 18, 2017
• 年：2017
• 卷：139
• 期：2
• 页码：701-707
• 全文大小：415K
• ISSN：1520-5126

文摘

MitoNEET is an outer membrane protein whose exact function remains unclear, though a role of this protein in redox and iron sensing as well as in controlling maximum mitochondrial respiratory rates has been discussed. It was shown to contain a redox active and acid labile [2Fe–2S] cluster which is ligated by one histidine and three cysteine residues. Herein we present the first synthetic analogue with biomimetic {SN/S<sub>2sub>} ligation which could be structurally characterized in its diferric form, 5<sup>2–sup>. In addition to being a high fidelity structural model for the biological cofactor, the complex is shown to mediate proton coupled electron transfer (PCET) at the {SN} ligated site, pointing at a potential functional role of the enzyme’s unique His ligand. Full PCET thermodynamic square schemes for the mitoNEET model 5<sup>2–sup> and a related homoleptic {SN/SN} capped [2Fe–2S] cluster 4<sup>2–sup> are established, and kinetics of PCET reactivity are investigated by double-mixing stopped-flow experiments for both complexes. While the N—H bond dissociation free energy (BDFE) of 5H<sup>2–sup> (230 ± 4 kJ mol<sup>–1sup>) and the free energy ΔG°<sub>PCETsub> for the reaction with TEMPO (−48.4 kJ mol<sup>–1sup>) are very similar to values for the homoleptic cluster 4H<sup>2–sup> (232 ± 4 kJ mol<sup>–1sup>, –46.3 kJ mol<sup>–1sup>) the latter is found to react significantly faster than the mitoNEET model (data for 5H<sup>2–sup>: k = 135 ± 27 M<sup>–1sup> s<sup>–1sup>, ΔH<sup>‡sup> = 17.6 ± 3.0 kJ mol<sup>–1sup>, ΔS<sup>‡sup> = −143 ± 11 J mol<sup>–1sup> K<sup>–1sup>, and ΔG<sup>‡sup> = 59.8 kJ mol<sup>–1sup> at 293 K). Comparison of the PCET efficiency of these clusters emphasizes the relevance of reorganization energy in this process.