Scientists design and assemble minimized artificial carbon fixation cycle

Scientists from the Institute of Microbiology of the Chinese Academy of Sciences (IMCAS) just lately reported a minimized artificial carbon fixation cycle. The cycle solely incorporates 4 biochemical reactions and is able to condensing two molecules of carbon dioxide into one molecule of oxalate in every spherical. The research was printed in ACS Catalysis.

The rising atmospheric carbon dioxide focus is among the main contributors to anthropogenic local weather change, which has aroused nice concern worldwide. In nature, crops and microbes repair carbon dioxide by way of carbon fixation pathways. Two artificial carbon fixation pathways, the crotonyl-CoA/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle and the substitute starch anabolic pathway (ASAP) pathway, have additionally been reported lately. However, these pathways normally include a number of reactions (largely greater than 10 reactions).

Generally, the massive variety of reactions could cut back the general carbon fixation effectivity of the pathway. Scientists then requested: is it potential to cut back the variety of reactions required for a carbon fixation cycle in order to extend the effectivity? and if potential, what’s the minimal variety of reactions that may represent a purposeful carbon fixation cycle?

To reply this query, scientists at IMCAS designed a minimized artificial carbon fixation cycle based mostly on thermodynamic and kinetic calculations of enzymatic reactions. This artificial cycle incorporates solely 4 reactions and the 4 enzymes concerned are pyruvate carboxylase (PYC), oxaloacetate acetylhydrolase (OAH), acetate-CoA ligase (ACS) and pyruvate synthase (PFOR), so this cycle was named the pyruvate carboxylase/oxaloacetate acetylhydrolase/acetate-CoA ligase/pyruvate:ferredoxin oxidoreductase (POAP) cycle.

The most difficult response within the POAP cycle was the reductive carboxylation of PFOR. Usually, PFOR catalyzes the oxidative decarboxylation of pyruvate. The reductive carboxylation response have to be pushed by a low-potential electron donor. Ferredoxin was chosen because the electron donor for this function. Among a sequence of low-potential ferredoxins examined, a ferredoxin from Hydrogenobacter thermophiles was discovered to effectively drive the reductive carboxylation of PFOR from Clostridium thermocellum. Subsequently, PYC, OAH and ACS had been screened for the development of POAP cycle.

To assemble the POAP cycle, 4 reactions had been divided into two cascades, then the 2 cascades had been assembled collectively, and the carbon fixation effectivity had been examined beneath anaerobic conditions utilizing ¹³C-labeled NaHCO₃ because the substrate. ¹³C-labeled oxalate produced by the POAP cycle was detected by liquid chromatography–mass spectrometry. The CO₂ fixation fee of the POAP cycle was calculated to be 8.0 ± 1.8 nmol CO₂ min^-1 mg^-1 CO₂-fixing enzymes and the total turnover quantity was 5 mol/mol enzymes, surpassing that of the artificial CETCH cycle.

The POAP cycle features beneath comparatively excessive temperature (50 levels Celsius) and anaerobic situations, so it might present a novel mannequin for understanding and investigating CO₂fixation in historic organisms. The POAP cycle additionally offers another pathway for biologically changing carbon dioxide into helpful chemical substances.