A new function in plant enzyme that could inspire a new form of green chemistry is discovered.
Researchers at the Brookhaven National Laboratory of the United States’ Department of Energy announced the discovery of a new function in a plant enzyme that could have implications for the design of new chemical catalysts.
According to John Shanklin, lead researcher of Brookhaven Lab Biochemist, “This enzyme could inspire a new form of green chemistry. A potential strategy that can be used in designing new bio-inspired catalysts to replace the more expensive, toxic catalysts currently available in the market today.
The discovery is through their ongoing research into enzymes that desaturate plant oils. These desaturase enzymes strip hydrogen atoms off specific adjacent carbon atoms in a hydrocarbon chain and insert a double bond between those carbon atoms. According to the study, they had previously created a triple mutant version of a desaturase enzyme with interesting properties, and they were studying the three mutations separately to see how each one functions.
Two of the single mutant enzymes turned out to remove the double bond between adjacent carbon atoms and added an “OH” (hydroxyl group) to each carbon to produce a fatty acid with two adjacent hydroxyl groups.
Fatty acids containing such adjacent OH groups, known as diols, are important chemical components for making lubricants, like those that keep hot engines running smoothly. They can also be converted to building blocks for making plastics or other commodity products — Where hazardous chemicals are being used. Hence the discovery of an organic enzyme would pave the way to green chemistry.
“Diols are really important industrial chemicals but making them artificially in the lab is quite problematic,” Shanklin said.
The best industrial catalysts for this reaction are expensive, highly volatile, and toxic, the researchers noted.
Likewise, there are distinct forms of diols, and it is hard for chemists to make a single pure form.
Meanwhile, The enzyme mutants discovered naturally make a single form, so it’s ready to use without further processing or waste.
Tracing the origins of the oxygen atoms in the two OH groups revealed that both came from the same oxygen molecule (O2). The ability to transfer both oxygen atoms from a single O2 molecule during a reaction, known as “dioxygenase” chemistry, was something of a surprise for a “diiron” enzyme (one with two iron atoms in its active site).
“Dioxygenase chemistry has not previously been reported for diiron enzymes,” Shanklin said. “We had to perform some technically challenging experiments to provide incontrovertible proof that this was indeed happening, and without Ed Whittle’s creativity and tenacity, we wouldn’t have completed this study.”
Whittle, the lead author on the paper (now retired from Brookhaven Lab), has diligently worked on this project over a period of years in Shanklin’s lab to nail down this important new discovery.
The team’s next goal is to obtain a crystal structure of this enzyme using x-rays at the National Synchrotron Light Source II (NSLS-II)—a DOE Office of Science user facility at Brookhaven Lab.
“We’ll share that structural information with our computational chemistry colleagues to figure out the details of how this unprecedented chemistry can occur with this class of catalyst.”
That work could help the team learn how to control the configuration of lab-made catalysts to mimic the plant-derived version.
“If we can incorporate what we’ve learned into the design of industrial catalysts, those reactions could produce purer products with less waste and avoid using toxic chemicals,” Shanklin said.
The enzyme catalyzes, are the cornerstone chemical reactions needed to synthesize a wide array of organic molecules, including those found in lubricants, cosmetics, and those used as raw materials for making plastics.
Meanwhile, green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use, and ultimate disposal. Green chemistry is also known as sustainable chemistry.
