Plug-and-play for improving primary productivity
Photosynthesis, the process in which light energy is captured and converted to chemical energy through the Calvin–Benson–Bassham (CBB) cycle is the foundation of the majority of global primary productivity. The first step of the CBB cycle involves the most abundant, and possibly the most problematic protein in the world, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The inability of RubisCO to discriminate between CO 2 and O 2 is considered the key limitation to photosynthetic efficiency; while the carboxylase activity converts CO 2 into organic carbon molecules used in biosynthesis, the competing oxygenase activity produces phosphoglycolate, which inhibits some CBB cycle enzymes and must be metabolized via the relatively energetically expensive process of photorespiration. Further, the cost of naturally occurring photorespiratory salvage pathways is compounded by the loss of fixed carbon and nitrogen. Enhancing photosynthesis via remedying the catalytic shortcomings of RuBisCO has long been a major research goal. Despite decades of effort to decrease its oxygenase activity, no work has significantly improved the catalytic properties of RuBisCO. Recent theoretical studies (Tcherkez et al., 2006; Savir et al., 2010) have suggested that RuBisCO may be “nearly perfectly optimized,” possibly explaining the dearth of progress in applying protein engineering to enhance the function RuBisCO. Is it possible to overcome the limitations in the product of billions of years of evolution?