Rubisco is arguably the most abundant—and most important—protein on Earth. This enzyme drives photosynthesis, the process that plants use to convert sunlight into energy to fuel crop growth and yield. Rubisco’s role is to capture and fix carbon dioxide (CO2) into sugar that fuels the plant’s activities. However, as much as Rubisco benefits plant growth, it also can operate at a notoriously slow pace that creates a hindrance to photosynthetic efficiency.
About 20 percent of the time Rubisco fixes oxygen (O2) molecules instead of CO2, costing the plant energy that could have been utilized to create yield. This time- and energy-consuming process is called photorespiration, where the plant sends its enzymes through three different compartments within the plant cell.
“However, many photosynthetic organisms have evolved mechanisms to overcome some of Rubisco’s limitations,” said Ben Long who led this recent study published in PNAS for a research project called Realizing Increased Photosynthetic Efficiency (RIPE). RIPE, which is led by Illinois in partnership with the Australian National University (ANU), is engineering crops to be more productive by improving photosynthesis. RIPE is supported by the Bill & Melinda Gates Foundation, Foundation for Food & Agriculture Research, and U.K. Foreign, Commonwealth & Development Office.
“Among these organisms are microalgae and cyanobacteria from aquatic environments, which have efficiently functioning Rubisco enzymes sitting inside liquid protein droplets and protein compartments called pyrenoids and carboxysomes,” said lead researcher Long from the ANU Research School of Biology.
How these protein compartments assist in the Rubisco function is not entirely known. The team from ANU aimed to find the answer by using a mathematical model that focused on the chemical reaction Rubisco carries out. As it collects CO2 from the atmosphere, Rubisco also releases positively charged protons.