A Minimized Synthetic Carbon Fixation Cycle

Natural CO 2 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 CO 2 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 CO 2 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 °C under anaerobic conditions, reaching a CO 2 fixation rate of 8.0 nmol CO 2 min –1 mg –1 CO 2 -fixing enzymes. The design and demonstration of the POAP cycle may provide a model to study CO 2 fixation in the earliest organisms.