Scientists report making an artificial chloroplast that operates outside of cells to harvest sunlight and use the resulting energy to convert carbon dioxide (CO2) into energy-rich molecules.
Synthetic biologists have remade chloroplasts, the engine at the heart of photosynthesis, by combining the light-harvesting machinery of spinach plants with enzymes from nine different organisms.
Photosynthesis is a two-step process. In chloroplasts, chlorophyll molecules absorb sunlight and pass the extra energy to molecular partners that use it to generate the energy-storing chemicals adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH).
A suite of other enzymes working in a complex cycle then use ATP and NADPH to convert CO2 from the air into glucose and other energy-rich organic molecules that the plant uses to grow.
CO2 conversion starts with an enzyme called RuBisCO, which prompts CO2 to react with a key organic compound, starting a chain of reactions needed to make vital metabolites in plants.
Each copy of the enzyme can grab and use just five to 10 CO2 molecules per second. That puts a speed limit on how fast plants can grow.
Researchers sought to ramp things up by designing a new set of chemical reactions. Instead of RuBisCO, they substituted a bacterial enzyme that can catch CO2 molecules and force them to react 10 times faster.
In combination with 16 other enzymes from nine different organisms, this created a new CO2-to-organic-chemical cycle they dubbed the CETCH cycle.
The enzymes convert the CO2 into a molecule called glycolate that can be used as a feedstock for making useful organic products.
Researchers hope to modify their setup further to produce other organic compounds that are even more valuable than glycolate, such as drug molecules. They also hope to more efficiently convert captured CO2 into organic compounds that plants need to grow.
That would open the door to engineering the genes for this novel photosynthesis pathway into crops to create novel varieties that grow much faster than current varieties—a boon for agriculture in a world with a booming population.