Altered enzymes transform plant waste into new products

A US–UK research team has engineered enzymes to perform an important step in the conversion of plant waste into sustainable and high-value products such as nylon, plastics and chemicals.

The study, published in the journal Proceedings of the National Academy of Sciences, details the newly engineered enzyme’s activity on lignin, a main component of plants. Lignin acts as scaffolding in plants and is central to water delivery, providing strength as well as defence against pathogens.

The discovery was led by members of the same UK–US team that engineered and improved a plastic-digesting enzyme in 2018, a potential breakthrough in the fight against plastic waste.

Professor John McGeehan, Director of the Centre for Enzyme Innovation in the School of Biological Sciences at Portsmouth University, said, “This is our goal — to discover enzymes from nature, bring them into our laboratories to understand how they work, then engineer them to produce new tools for the biotechnology industry.

“In this case, we have taken a naturally occurring enzyme and engineered it to perform a key reaction in the breakdown of one of the toughest natural plant polymers.

“To protect their sugar-containing cellulose, plants have evolved a fascinatingly complicated material called lignin that only a small selection of fungi and bacteria can tackle. However, lignin represents a vast potential source of sustainable chemicals, so if we can find a way to extract and use those building blocks, we can create great things,” Prof McGeehan explained.

Current enzymes tend to work on only one of the building blocks of lignin, making the breakdown process inefficient. Using 3D structural and biochemical techniques, the research team altered the shape of the enzyme to accommodate multiple building blocks. The results provide a route to making new materials and chemicals such as nylon, bioplastics and even carbon fibre, from what has previously been a waste product.

University of Portsmouth postgraduate student Dan Hinchen said, “We used X-ray crystallography at the Diamond Light Source synchrotron to solve 10 enzyme structures in complex with lignin building blocks. This gave us the blueprint to engineer an enzyme to work on new molecules. Our colleagues were then able to transfer the DNA code for this new enzyme into an industrial strain of bacteria, extending its capability to perform multiple reactions.”

“It’s an amazing material,” added Prof McGeehan. “Cellulose and lignin are among the most abundant biopolymers on Earth. The success of plants is largely due to the clever mixture of these polymers to create lignocellulose, a material that is challenging to digest.”

The discovery offers additional environmental benefits — creating products from lignin reduces our reliance on oil to make everyday products and offers an attractive alternative to burning it, helping to reduce CO₂ emissions.

Image credit: ©stock.adobe.com/au/Laura Pashkevich