A Minimized Synthetic Carbon Fixation Cycle

Natural CO2 fixation cycles usually comprise multiple reactions, which may reduce the efficiency of the cycle. Here, we report the design and experimental demonstration of a minimized synthetic CO2 fixation cycle which contains only four reactions. The cycle comprises pyruvate carboxylase, oxaloacetate acetylhydrolase, acetate-CoA ligase, and pyruvate synthase and is named the POAP cycle. The POAP cycle can condense two molecules of CO2 into one molecule of oxalate in each step at the expense of two molecules of ATP and one reducing equivalent in the form of NAD(P)H. By identifying a ferredoxin from Hydrogenobacter thermophilus that can efficiently drive the rate-limiting reductive carboxylation step, the POAP cycle can be operated at 50 degrees C under anaerobic conditions, reaching a CO2 fixation rate of 8.0 nmol CO2 min(-1) mg(-1) CO2-fixing enzymes. The design and demonstration of the POAP cycle may provide a model to study CO2 fixation in the earliest organisms.