Improving CO₂ fixation by enhancing rubisco performance

The photosynthetic enzyme linking the inorganic and organic phases of the biosphere is ribulose-1,5-bisphosphate [RuBP] carboxylase/oxygenase (Rubisco). The complicated catalytic chemistry of Rubisco slows its CO2 fixation rate, allows for competitive inhibition by oxygen and permits the production of misfire products that can self-inhibit activity. Significant effort has been invested into better understanding the structure-function details of Rubisco as improving its performance is recognised as a viable means to enhance the photosynthetic efficiency and yield potential of crops. While rational design approaches have still been unable to provide catalysis enhancing solutions, modern directed evolution tools are posing a promising conduit to improving Rubisco. Advances in the design of effective selection systems for mutagenic Rubisco library screening have strategically increased their focus on using Escherichia coli. The inherent sensitivity of E. coli viability to the pentose sugar substrate of Rubisco, RuBP, is being exploited in an increasingly effective manner to select for Rubisco mutants with increased activity. Here we review the differing directed evolution technologies used to evolve Rubisco, examine the merits of available highthroughput Rubisco-dependent E. coli (RDE) selection systems and postulate approaches for improving their functionality.