Fuel from carbohydrates

A group of researchers unravel the mechanism of action of an enzyme that can be used to break down cellulose into useful biofuels. 

Carbohydrates are made up of long chains of sugars that can be broken down by the help of enzymes to release energy. Some carbohydrates such as plant cellulosic materials, however, are recalcitrant, but their abundance as a potential renewable energy source has motivated an extensive search for enzymes that can efficiently break them down.

While several such enzymes had been identified, a specific class of metal-containing enzymes, known as lytic polysaccharide monooxygenases (LPMOs), shown to significantly boost the activity of conventional enzymes used in biorefineries‬, holds particular promise. 

To better understand how this class of enzymes works, an international team of researchers solved the atomic structure of a representative LPMO together with its carbohydrate substrate by X-ray crystallography, publishing their results in Nature Chemical Biology.

‪”LPMOs have been the subject of tremendous attention since their discovery only a few years ago,” says Leila Lo Leggio, who co-led the study. “I am fascinated by these enzymes and 'seeing' them in action, in a high resolution crystal structure in complex with their substrate has been a major goal and a major highlight of my research of the last few years.”‬‬‬‬‬

Her team additionally used a labelled carbohydrate that produces a fluorescent signal when cleaved to follow the rate of the carbohydrate lysis reaction catalysed by the enzyme, and then went on to use electron paramagnetic resonance (EPR) spectroscopy to investigate how the electronic environment of the active site metal changes upon substrate binding. 

Together, these data reveal a new mechanism of carbohydrate substrate binding and catalysis.

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