Reconstructing CO2 fixation from the past : analysis of Rubisco evolution could inform how to engineer a better enzyme

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is the central CO2-fixing enzyme of photosynthesis and often limits the rate of carbon assimilation for key agricultural crops. Rubisco is catalytically feeble because of its slow catalytic speed (1 to 9 catalytic cycles per second), low affinity for CO2, and low specificity for CO2 compared with O2. These catalytic parameters strongly influence crop water and nitrogen use required for efficient growth of photosynthetic organisms. The decline in CO2 and the concomitant rise of O2 in Earth’s atmosphere led to the independent evolution of carbon-concentrating mechanisms across lineages of photosynthetic organisms to improve Rubisco catalysis by increasing CO2 around the active site while effectively suppressing oxygenation. On page 155 of this issue, Schulz et al. report the ancestral reconstruction of Rubisco to predict early isoforms and the functional adaptation that enabled sufficient carbon fixation in the face of rising O2 in Earth’s atmosphere.