A bacterial flavin‐dependent oxidoreductase that captures carbon dioxide into biomass
- Montana State University Bozeman MT
- Montana State University Bozeman MT, Washington State University Pullman WA
- Washington State University Pullman WA
Atmospheric carbon dioxide is used as a carbon source for building biomass in plants and photosynthetic microbes. Non‐photosynthetic processes that also fix carbon dioxide have more recently been discovered. This research focuses on a microbial mechanism for coupling acetone to CO 2 to make a central metabolite, acetoacetate. The key reaction is catalyzed by NADPH‐2‐ketopropyl‐coenzyme M oxidoreductase/carboxylase (2‐KPCC), a bacterial enzyme that is part of the flavin and cysteine‐disulfide containing oxidoreductase family (DSORs) which are best known for reducing metallic or disulfide substrates. Our research asks: how has nature repurposed a DSOR to, uniquely, break a C‐S bond and then trap and fix CO 2 ? 2‐KPCC lacks a conserved, catalytically essential acid‐base histidine possessed by all other DSOR enzymes, having instead a phenylalanine (F501) at the same position. Mutagenesis showed that a F501H mutant has a similar rate of catalytic turnover; however, the product is acetone instead of acetoacetate (Figure 1). We hypothesized that F501 is important for both the reductive half reaction – which generates the reactive, C‐S bond breaking form of the active site – and for the oxidative half, in which an enolacetone intermediate reacts with either the correct (CO 2 ) or incorrect (H + ) electrophile. In this study, we used real‐time and spectroscopic methods to examine the reductive half reaction. In typical DSORs, this reaction generates a Cys/FAD charge transfer species. However, we showed that 2‐KPCC generates an electronically unique form of the active site, in which the flavin is oxidized and a pair of active site histidines are reduced and protonated. We hypothesize that this form of the active site generates the substrate‐reactive Cys in a more nucleophilic form, where it is capable of cleaving relatively strong C‐S bonds. The resulting enolacetone carbanion is an extremely potent nucleophile that is capable of directly attacking CO 2 . Research on 2‐KPCC and other biological CO 2 fixation methods adds to our arsenal of strategies for carbon dioxide capture and use.
Support or Funding Information
DOE:DE‐FG02‐04ER15563
This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- FG02-04ER15563
- OSTI ID:
- 1786869
- Journal Information:
- FASEB Journal, Journal Name: FASEB Journal Journal Issue: S1 Vol. 32; ISSN 0892-6638
- Publisher:
- FASEBCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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