APBN New Site

APBN Developing Site

New Synthetic Enzyme That Breaks Down Rigid, Woody Lignin

The development of such an enzyme opens new avenues for exploration for the use of lignin as a renewable source of energy.

Lignin is the second-largest component in lignocellulosic plant biomass, but its full energy potential has not been properly harnessed as it has been unyielding to previous attempts to convert it into other useful compounds. Furthermore, when used as fuel, the carbon that makes up the bulk of it is released into the atmosphere upon combustion instead of being appropriated for other uses.

Thus, a group of researchers from Washington State University and the Department of Energy’s Pacific Northwest National Laboratory have set out to remedy this issue with their efforts cumulating in the successful creation of an artificial enzyme that can digest lignin. Their findings were published in Nature Communications.

“Our bio-mimicking enzyme showed promise in degrading real lignin, which is considered to be a breakthrough,” said Xiao Zhang, a corresponding author on the paper and associate professor in WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering. “We think there is an opportunity to develop a new class of catalysts and to really address the limitations of biological and chemical catalysts.”

Lignin is present in all vascular plants, being used in cell walls, to provide structure and support to plants. It is the compound that is responsible for the firm texture of vegetables and enables trees to stand upright, making up 20 to 30 per cent of the weight of wood.

Despite over 100 years of experimentation by chemists, lignin has yet to be used in the synthesis of more valuable products. But that unlucky streak may finally be ended with the development of a synthetic enzyme that breaks down lignin.

Nature does offer some insights into enzymes with the ability to break down lignin as they are produced by some species of fungi and bacteria that are responsible for the decomposition of wood. The breakdown of lignin by enzymes offers a more environmentally friendly alternative to chemical degradation, which is extremely energy inefficient.

Unfortunately, the main disadvantages of biological enzymes are that they are costly, difficult to produce in large quantities, and degrade easily when isolated. To address these issues, the team developed a synthetic enzyme to break down lignin, where the peptides in the active sites of the natural enzymes were swapped out for peptoids—modified amino acid chains—that are more resistant to proteolytic degradation. These peptoids then self-assemble into crystalline sheets and tubes at the nanoscale, allowing for a higher density of active sites per enzyme.

These modified enzymes are more heat-stable and resistant to degradation and may work at temperatures up to 60°C compared to a natural enzyme that would be deactivated at that temperature.

“This work really opens up new opportunities,” said Chun-Long Chen, a corresponding author, a Pacific Northwest National Laboratory researcher, and affiliate professor in chemical engineering and chemistry at the University of Washington. “This is a significant step forward in being able to convert lignin into valuable products using an environmentally benign approach.”

If the enzyme may be further improved to increase conversion yield or generate more high-value products selectively, it may show promise for use on an industrial scale. This could yield breakthroughs in more sustainable sources of aviation biofuel and other biological materials, bringing us closer to a circular economy. [APBN]

Source: Jian et al. (2022). Highly stable and tunable peptoid/hemin enzymatic mimetics with natural peroxidase-like activities. Nature Communications, 13, 3025.