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Abstract Oxalate decarboxylase fromBacillus subtilisis 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.
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Oxalate and oxalotrophy: an environmental perspective
Abstract Oxalic acid is one of the most abundant organic acids produced by plants. Much of the global production of oxalic acid is deposited on soil surfaces in leaf litter to be oxidized by microorganisms, resulting in a pH increase and shifting the carbonate equilibria. In what is known as the oxalate-carbonate pathway, calcium oxalate metabolism results in CO2 being sequestered into soils as insoluble calcite (CaCO3). There is a growing appreciation that the global scale of this process is sufficiently large to be an important contribution to global carbon turnover budgets. The microbiomics, genetics, and enzymology of oxalotrophy are all soundly established, although a more detailed understanding of the landscape-scale kinetics of the process would be needed to incorporate oxalotrophy as an element of process models informing the relevant Sustainable Development Goals. Here, we review the current state of knowledge of oxalotrophs and oxalotrophy and the role they play in terrestrial ecosystem services and functions in terms of carbon sequestration and nutrient cycling. We emphasize the relevance of these to the Sustainability Development Goals (SDGs) and highlight the importance of recognizing oxalotrophy, when accounting for the natural capital value of an ecosystem.
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- PAR ID:
- 10487416
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Sustainable Microbiology
- Volume:
- 1
- Issue:
- 1
- ISSN:
- 2755-1970
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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