Food & Climate
MIT researchers plan to apply a new technique to species of rubisco, the enzyme that catalyzes photosynthesis, which could be used in plants to help boost their photosynthesis rates, potentially leading to a leap in agricultural production.
Photosynthesis is a process used by plants, algae, and some bacteria to convert light energy, typically from the sun, into chemical energy in the form of glucose. This process utilizes carbon dioxide and water, releasing oxygen as a byproduct. Photosynthesis is vital for life on Earth, providing the foundation of most food chains and maintaining the balance of oxygen and carbon dioxide in the atmosphere.
MIT scientists have reengineered rubisco that has long frustrated scientists with its sluggish performance.
Using a cutting-edge technique called continuous directed evolution, they boosted the enzyme’s efficiency by up to 25%. This lab-evolved rubisco resists oxygen interference and could pave the way for faster-growing crops, more efficient plants, and a potential leap in agricultural production worldwide, according to a report seen by “Food & Climate” platform.
During photosynthesis, an enzyme called rubisco catalyzes a key reaction — the incorporation of carbon dioxide into organic compounds to create sugars. However, rubisco, which is believed to be the most abundant enzyme on Earth, is very inefficient compared to the other enzymes involved in photosynthesis.
Enhance a version of rubisco
MIT chemists have now shown that they can greatly enhance a version of rubisco found in bacteria from a low-oxygen environment. Using a process known as directed evolution, they identified mutations that could boost rubisco’s catalytic efficiency by up to 25%.
“This is, I think, a compelling demonstration of successful improvement of a rubisco’s enzymatic properties, holding out a lot of hope for engineering other forms of rubisco,” says Matthew Shoulders, the Class of 1942 Professor of Chemistry at MIT.
Shoulders and Robert Wilson, a research scientist in the Department of Chemistry, are the senior authors of the new study, which was published in the Proceedings of the National Academy of Sciences. MIT graduate student Julie McDonald is the paper’s lead author.
Compared to the other enzymes involved in photosynthesis, rubisco is very slow, catalyzing only one to 10 reactions per second. Additionally, rubisco can also interact with oxygen, leading to a competing reaction that incorporates oxygen instead of carbon — a process that wastes some of the energy absorbed from sunlight.
Previous research has led to improvement in rubisco’s stability and solubility, which resulted in small gains in enzyme efficiency. Most of those studies used directed evolution — a technique in which a naturally occurring protein is randomly mutated and then screened for the emergence of new, desirable features.
Loss of 30% of sunlight energy
The MIT team used a newer mutagenesis technique that the Shoulders Lab previously developed, called MutaT7. This technique allows the researchers to perform both mutagenesis and screening in living cells, which dramatically speeds up the process. Their technique also enables them to mutate the target gene at a higher rate.
After six rounds of directed evolution, the researchers identified three different mutations that improved the rubisco’s resistance to oxygen. Each of these mutations are located near the enzyme’s active site (where it performs carboxylation or oxygenation).
The researchers believe that these mutations improve the enzyme’s ability to preferentially interact with carbon dioxide over oxygen, which leads to an overall increase in carboxylation efficiency.
“The underlying question here is: Can you alter and improve the kinetic properties of rubisco to operate better in environments where you want it to operate better?” Shoulders says. “What changed through the directed evolution process was that rubisco began to like to react with oxygen less. That allows this rubisco to function well in an oxygen-rich environment, where normally it would constantly get distracted and react with oxygen, which you don’t want it to do.”
In ongoing work, the researchers are applying this approach to other forms of rubisco, including rubisco from plants. Plants are believed to lose about 30% of the energy from the sunlight they absorb through a process called photorespiration, which occurs when rubisco acts on oxygen instead of carbon dioxide.
“This really opens the door to a lot of exciting new research, and it’s a step beyond the types of engineering that have dominated rubisco engineering in the past,” Wilson says. “There are definite benefits to agricultural productivity that could be leveraged through a better rubisco.”
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