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Selective incorporation of 5-hydroxytryptophan blocks long range electron transfer in oxalate decarboxylase

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Drosou,  Maria
Research Group Pantazis, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Pantazis,  Dimitrios A.
Research Group Pantazis, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Pastore, A. J., Montoya, A., Kamat, M., Basso, K. B., Italia, J. S., Chatterjee, A., et al. (2023). Selective incorporation of 5-hydroxytryptophan blocks long range electron transfer in oxalate decarboxylase. Protein Science, 32(1): e4537. doi:10.1002/pro.4537.


Cite as: https://hdl.handle.net/21.11116/0000-000C-8261-3
Abstract
Oxalate decarboxylase from Bacillus subtilis is a binuclear Mn-dependent acid stress response enzyme that converts the mono-anion of oxalic acid into formate and carbon dioxide in a redox neutral unimolecular disproportionation reaction. A π-stacked tryptophan dimer, W96 and W274, at the interface between two monomer subunits facilitates long-range electron transfer between the two Mn ions and plays an important role in the catalytic mechanism. Substitution of W96 with the unnatural amino acid 5-hydroxytryptophan leads to a persistent EPR signal which can be traced back to the neutral radical of 5-hydroxytryptophan with its hydroxyl proton removed. 5-Hydroxytryptophan acts as a hole sink preventing the formation of Mn(III) at the N-terminal active site and strongly suppresses enzymatic activity. The lower boundary of the standard reduction potential for the active site Mn(II)/Mn(III) couple can therefore be estimated as 740 mV against the normal hydrogen electrode at pH 4, the pH of maximum catalytic efficiency. Our results support the catalytic importance of long-range electron transfer in oxalate decarboxylase while at the same time highlighting the utility of unnatural amino acid incorporation and specifically the use of 5-hydroxytryptophan as an energetic sink for hole hopping to probe electron transfer in redox proteins.