Augmenting the Calvin–Benson–Bassham cycle by a synthetic malyl-CoA-glycerate carbon fixation pathway

Abstract

The Calvin–Benson–Bassham (CBB) cycle is presumably evolved for optimal synthesis of C3 sugars, but not for the production of C2 metabolite acetyl-CoA. The carbon loss in producing acetyl-CoA from decarboxylation of C3 sugar limits the maximum carbon yield of photosynthesis. Here we design a synthetic malyl-CoA-glycerate (MCG) pathway to augment the CBB cycle for efficient acetyl-CoA synthesis. This pathway converts a C3 metabolite to two acetyl-CoA by fixation of one additional CO2 equivalent, or assimilates glyoxylate, a photorespiration intermediate, to produce acetyl-CoA without net carbon loss. We first functionally demonstrate the design of the MCG pathway in vitro and in Escherichia coli. We then implement the pathway in a photosynthetic organism Synechococcus elongates PCC7942, and show that it increases the intracellular acetyl-CoA pool and enhances bicarbonate assimilation by roughly 2-fold. This work provides a strategy to improve carbon fixation efficiency in photosynthetic organisms.

Update: Improving the Efficiency of Photosynthetic Carbon Reactions

“…While pyruvate can potentially be exported to the cytosol, converted to 3PGA or triose phosphate, and imported back into the chloroplast, the complexity of this route renders it quite unlikely to be useful. Another recent study put forward the synthetic malyl-CoAglycerate cycle as a way to convert glycolate to acetyl-CoA (Yu et al, 2018). While this pathway could be useful for the biosynthesis of chemicals that originate from acetyl-CoA, it cannot be considered a true PR bypass as acetyl-CoA cannot be easily reassimilated to the CBC.…”

Engineering photoautotrophic carbon fixation for enhanced growth and productivity

“…Even though there are no reports about introducing new complete CO 2 xation pathways into photoautotrophic organisms, there is one example of an articial pathway to compensate the CO 2 loss when pyruvate is converted into acetyl-CoA in Synechococcus elongates PCC 7942. 108…”

Recent Advances in Developing Artificial Autotrophic Microorganism for Reinforcing CO2 Fixation

“…Like the abovementioned C4 metabolites, acetyl-CoA can also be produced from C3 metabolites. A synthetic malonyl-CoA-glycerate (MCG) pathway has been demonstrated to be an efficient way to produce acetyl-CoA ( Yu et al, 2018 ). First, two molecules of PEP were carboxylated into two molecules of oxaloacetate by inputting two molecules of bicarbonate.…”