Rubisco, the imperfect winner: it's all about the base

The evolution of Rubisco as the dominant CO2-fixing enzyme of oxygenic photosynthesis has involved overcoming a number of limiting imperfections. The solutions to and consequences of these problems are highlighted. Rubisco catalysis is complex and includes an activation step through the formation of a carbamate at the conserved active site lysine residue and the formation of a highly reactive enediol that is the key to its catalytic reaction. The formation of this enediol is both the basis of its success and its Achilles' heel, creating imperfections to its catalytic efficiency. While Rubisco originally evolved in an atmosphere of high CO2, the earth's multiple oxidation events provided challenges to Rubisco through the fixation of O-2 that competes with CO2 at the active site. Numerous catalytic screens across the Rubisco superfamily have identified significant variation in catalytic properties that have been linked to large and small subunit sequences. Despite this, we still have a rudimentary understanding of Rubisco's catalytic mechanism and how the evolution of kinetic properties has occurred. This review identifies the lysine base that functions both as an activator and a proton abstractor to create the enediol as a key to understanding how Rubisco may optimize its kinetic properties. The ways in which Rubisco and its partners have overcome catalytic and activation imperfections and thrived in a world of high O-2, low CO2, and variable climatic regimes is remarkable.

Automated summary

This article discusses the challenges and solutions in the evolution of Rubisco as a CO2-fixing enzyme, highlighting the importance of its catalytic mechanism and kinetic properties. Despite the incomplete understanding of Rubisco, it and its partners have achieved remarkable success in high O-2, low CO2, and variable climatic conditions.