Woody lignin, seen here in purified form, is an important promise as a renewable biofuel, if it can be decomposed efficiently in a useful way. Credit: Andrea Starr | Pacific Northwest National Laboratory
A new artificial enzyme has been shown to chew lignin, the resistant polymer that helps woody plants maintain their shape. Lignin also stores great potential for energy and renewable materials.
Report in the magazine Communications of natureA team of researchers from Washington State University and the Northwest Pacific National Laboratory of the Department of Energy showed that their artificial enzyme was able to digest lignin, which has stubbornly resisted previous attempts to convert it is an economically useful source of energy.
Lignin, the second most abundant renewable carbon source on Earth, is mostly wasted as a fuel source. When firewood is burned for cooking, the by-products of lignin help impart this smoky flavor to food. But burning releases all this carbon into the atmosphere instead of capturing it for other uses.
“Our biodiversity-enhancing enzyme was promising in the degradation of real lignin, which is considered a breakthrough,” said Xiao Zhang, author of the paper and associate professor at the School of Chemical Engineering and Bioengineering. WSU and Linda Voiland. Zhang also has a joint appointment with the PNNL. “We believe there is an opportunity to develop a new class of catalysts and to truly address the limitations of biological and chemical catalysts.”
Lignin is found in all vascular plants, where it forms cell walls and provides stiffness to plants. Lignin allows trees to be maintained, gives firmness to vegetables, and accounts for about 20-35% of the weight of wood. Because lignin turns yellow when exposed to air, the wood products industry removes it as part of the fine paper manufacturing process. Once removed, it is often burned inefficiently to produce fuel and electricity.
Chemists have tried and failed for over a century to make valuable products from lignin. This history of frustration may be about to change.
Better than nature
“This is the first mimetic enzyme in nature that we know can efficiently digest lignin to produce compounds that can be used as biofuels and for chemical production,” added Chun-Long Chen, lead author and researcher at Pacific Northwest National Laboratory and affiliate. professor of chemical and chemical engineering at the University of Washington.
In nature, fungi and bacteria are able to break down lignin with their enzymes, which is how a trunk covered with mushrooms in the forest breaks down. Enzymes offer a much more environmentally benign process than chemical degradation, which requires a lot of heat and consumes more energy than it produces.
However, natural enzymes degrade over time, making them difficult to use in an industrial process. They are also expensive.
“It is very difficult to produce these enzymes from microorganisms in a significant amount for practical use,” Zhang said. “Then, once isolated, they are very fragile and unstable. But these enzymes provide a great opportunity to inspire models that copy their basic design.”
Although researchers have not been able to take advantage of natural enzymes to work for them, they have learned a great deal about how they work over the decades. A recent review article by Zhang’s research team describes the challenges and barriers to the application of lignin-degrading enzymes. “Understanding these barriers provides new insights into the design of biomimetic enzymes,” Zhang added.
Researchers Xiao Zhang (L) and Chun-long Chen (R) examine the products of lignin digestion using their new biomimetic peptoid catalyst. Credit: Andrea Starr | Pacific Northwest National Laboratory
Peptide scaffolding is key
In the current study, researchers replaced the peptides surrounding the active site of natural enzymes with protein-like molecules called peptoids. These peptoids then self-assembled into nanoscale crystalline tubes and sheets. Peptoids were first developed in the 1990s to mimic the function of proteins. They have several unique features, including high stability, that allow scientists to address deficiencies in natural enzymes. In this case, they offer a high density of active sites, which is impossible to obtain with a natural enzyme.
“We can accurately organize these active sites and adjust their local environments for catalytic activity,” Chen said, “and we have a much higher density of active sites, rather than an active site.”
As expected, these artificial enzymes are also much more stable and robust than natural versions, so they can work at temperatures of up to 60 degrees Celsius, a temperature that would destroy a natural enzyme.
“This job really opens up new opportunities,” Chen said. “This is an important step in being able to turn lignin into valuable products through an environmentally friendly approach.”
If the new biomimetic enzyme can be further improved to increase conversion performance, to generate more selective products, it has the potential to increase it on an industrial scale. The technology offers new routes to renewable materials for aviation biofuels and bio-based materials, among other applications.
Research collaboration was facilitated through the WSU-PNNL Bioproducts Institute. Tengyue Jian, Wenchao Yang, Peng Mu, Xin Zhang of PNNL and Yicheng Zhou and Peipei Wang of WSU also contributed to the investigation.
Researchers are isolating new types of microorganisms that cut ether bonds in a lignin-based compound. More information: Highly stable and adjustable peptoid / hemin enzyme mimetics with peroxidase-like natural activities. Communications of nature (2022). DOI: 10.1038 / s41467-022-30285-9 Provided by Pacific Northwest National Laboratory
Citation: The new artificial enzyme breaks down hard, woody lignin: The study shows promise for developing a new renewable energy source (2022, May 31) recovered on May 31, 2022
This document is subject to copyright. Apart from any fair treatment for private study or research purposes, no part may be reproduced without the written permission. Content is provided for informational purposes only.