MSU scientists part of international team that discovers new tool to break down plant waste

Two Montana State University researchers were part of an international team that discovered a new class within an important family of enzymes that could speed up the process of converting plant waste into useful products.

The enzymes, together called cytochrome P450, can efficiently break down five compounds found in woody plants, said Melodie Machovina, a doctoral student in Jennifer DuBois' laboratory in the Department of Chemistry and Biochemistry in MSU’s College of Letters and Science.

"That was really cool and surprising," Machovina said.

Since hundreds — or even thousands — of other enzymes can break down only one or two compounds, cytochrome P450 offers a new tool for a critical step in converting lignin into fuel, plastic, nylon and other useful materials, she added. Lignin is a vast source of renewable carbon. It is found in the cell walls of plants, causing them to become rigid, woody and more resistant to rot.

Machovina and DuBois, along with 12 partners in the United Kingdom, Brazil and elsewhere in the United States, described the new P450 system in a paper published this summer in the scientific journal Nature Communications. They said it was a promising approach to bioconversion and a significant breakthrough in a long struggle to find a way to break down the compounds in lignin so they can be converted into new materials and chemicals. The two main compounds in lignin — coniferyl and sinapyl — are often part of a key bottleneck in the conversion process.

"We now have one of the most well-known, versatile, engineerable and evolvable classes of enzymes ready to go as a foothold for biotechnology to move forward and make the enzyme better," co-author and principal investigator Gregg Beckham said in a Phys.org article about the discovery.

DuBois, an associate professor at MSU who is also a principal investigator on the project, compared lignin-eating bacteria to an animal eating corn on the cob. Like an animal trying to swallow the cob when it can only digest corn, some bacteria have problems breaking down the compounds that make up lignin.

Other bacteria and fungi, however, have enzymes that allow them to eat lignin, DuBois said. Trying to understand the mechanisms behind that valuable ability, the enzyme researchers conducted a variety of structural, biochemical and computational studies.

Machovina's role was examining and characterizing proteins that Sam Mallinson — a U.K. graduate student and co-lead author of the paper — created. Machovina wanted to see how fast and efficient they were at breaking down lignin, and how promising they were for large-scale production.

Speed and cost-effectiveness are important when converting lignin to useful products on an industrial scale, Machovina said.

"Time is money," she noted.

Machovina became involved in the enzyme project after receiving a fellowship from the U.S. Department of Energy, specifically its Office of Science Graduate Student Research. The fellowship allowed her to spend nine months last year at the National Renewable Energy Laboratory, or NREL, in Golden, Colorado, where she met Beckham from the NREL's National Bioenergy Center and John McGeehan from the University of Portsmouth in the U.K. They told her about the enzyme project, and she decided to join their research team. Mallinson is McGeehan's graduate student.

"It sounded like it would have applications and turned out to be really productive," Machovina said of the project.

Machovina said that after reading Nancy Drew and Sherlock Holmes books as a young girl, she wanted to be a detective and solve mysteries. When she took science classes, she realized she could solve mysteries on a molecular scale. She was especially drawn to biochemistry and enzymes, a field she will continue to pursue after she graduates this year and takes a postdoctoral position at the University of Illinois at Urbana-Champaign.

"I thought enzymes were so cool," Machovina said. "All kingdoms of life have them ... They are like little machines in our bodies. They keep us going. I was really fascinated with that."