A better way to break down cellulose

Scientists have gained new insight into the functioning of hydrolytic enzymes, in a study that could pave the way to more competitive biofuels.

The current technical complexity and costs of obtaining biofuels from biomass restrict their cheap, efficient and sustainable production. At a time when oil prices are at record lows, this is hindering their ability to compete on the fuels market.

One of the major challenges is breaking down cellulose, a polysaccharide and plant constituent which is not water soluble and thus difficult to process.

Biorefineries use a mix of hydrolytically active enzymes which utilise water molecules to break down plant materials, replicating the natural degradation processes. Recently, oxidative enzymes were discovered which utilise oxygen and work together with hydrolytic enzymes to break down cellulose more efficiently. Scientists at the Graz University of Technology are now working to find out how this process works.

Using atomic force microscopy, the researchers were able to observe enzymes at work on the surface of cellulose particles for the first time and provide direct evidence of their activity. The insights gained have been published in the journal Nature Communications.

As well as observing the actions of the hydrolytically active enzyme Trichoderma reesei CBH I, the researchers were able to observe how the behaviour of the enzyme changed when oxidative enzymes, also known as LPMOs (lytic polysaccharide monooxygenases), were added to mix. The Graz scientists established both that the LPMOS generated more binding sites on the surface of the hydrolytically active enzymes, and that the enzyme dynamics on the surface increased considerably.

“This study will contribute to a better understanding of these processes at a basic research level, and in a further step will facilitate the production of biofuels. Usually, in chemistry we are focused on soluble products, which can be easily measured, to deepen the understanding of a reaction. However, for a reaction taking place on a solid surface such an approach is not feasible. We wanted to observe and document the step before that, that is, the process of cellulose breakdown," says Manuel Eibinger, lead author of the study at the Institute of Biotechnology and Biochemical Engineering.

Bernd Nidetzky, head of the Institute of Biotechnology and Biochemical Engineering at TU Graz: "The saying comes to mind 'a picture is worth a thousand words'. In this study we wanted to document the processes as they occur in time. And this is what we managed to do."

The team’s study is available from Nature Communications, here.