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The H-bond network surrounding the pyranopterins modulates redox cooperativity in the molybdenum-bisPGD cofactor in arsenite oxidase

Duval, S; Santini, JM; Lemaire, D; Chaspoul, F; Russell, MJ; Grimaldi, S; Nitschke, W; (2016) The H-bond network surrounding the pyranopterins modulates redox cooperativity in the molybdenum-bisPGD cofactor in arsenite oxidase. Biochimica et Biophysica Acta - Bioenergetics , 1857 (9) pp. 1353-1362. 10.1016/j.bbabio.2016.05.003. Green open access

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Abstract

While the molybdenum cofactor in the majority of bisPGD enzymes goes through two consecutive 1-electron redox transitions, previous protein-film voltammetric results indicated the possibility of cooperative (n=2) redox behavior in the bioenergetic enzyme arsenite oxidase (Aio). Combining equilibrium redox titrations, optical and EPR spectroscopies on concentrated samples obtained via heterologous expression, we unambiguously confirm this claim and quantify Aio's redox cooperativity. The stability constant, Ks, of the Mo(V) semi-reduced intermediate is found to be lower than 10(-3). Site-directed mutagenesis of residues in the vicinity of the Mo-cofactor demonstrates that the degree of redox cooperativity is sensitive to H-bonding interactions between the pyranopterin moieties and amino acid residues. Remarkably, in particular replacing the Gln-726 residue by Gly results in stabilization of (low-temperature) EPR-observable Mo(V) with KS=4. As evidenced by comparison of room temperature optical and low temperature EPR titrations, the degree of stabilization is temperature-dependent. This highlights the importance of room-temperature redox characterizations for correctly interpreting catalytic properties in this group of enzymes. Geochemical and phylogenetic data strongly indicate that molybdenum played an essential biocatalytic roles in early life. Molybdenum's redox versatility and in particular the ability to show cooperative (n=2) redox behavior provide a rationale for its paramount catalytic importance throughout the evolutionary history of life. Implications of the H-bonding network modulating Molybdenum's redox properties on details of a putative inorganic metabolism at life's origin are discussed.

Type: Article
Title: The H-bond network surrounding the pyranopterins modulates redox cooperativity in the molybdenum-bisPGD cofactor in arsenite oxidase
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.bbabio.2016.05.003
Publisher version: http://dx.doi.org/10.1016/j.bbabio.2016.05.003
Language: English
Additional information: Copyright © 2016 Published by Elsevier B.V. This manuscript version is made available under the CC-BY-NC-ND 4.0 license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The published article is available at http://dx.doi.org/10.1016/j.bbabio.2016.05.003
Keywords: Arsenite oxidase, EPR spectroscopy, Molybdenum enzyme, optical spectroscopy, redox titrations
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Structural and Molecular Biology
URI: http://discovery.ucl.ac.uk/id/eprint/1492961
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