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Recycling hope for plastic-hungry enzyme

From BBC - April 16, 2018

Scientists have improved a naturally occurring enzyme which can digest some of our most commonly polluting plastics.

PET, the strong plastic commonly used in bottles, takes hundreds of years to break down in the environment.

The modified enzyme, known as PETase, can start breaking down the same material in just a few days.

This could revolutionise the recycling process, allowing plastics to be re-used more effectively.

UK consumers use around 13 billion plastic drinks bottles a year but more than three billion are not recycled.

Found in a dump

Originally discovered in Japan, the enzyme is produced by a bacterium which "eats" PET.

Ideonella sakaiensis uses the plastic as its major energy source.

Researchers reported in 2016 that they had found the strain living in sediments at a bottle recycling site in the port city of Sakai.

"[PET] has only been around in vast quantities over the last 50 years, so it's actually not a very long timescale for a bacteria to have evolved to eat something so man-made," commented Prof John McGeehan, who was involved in the current study.

Polyesters, the group of plastics that PET (also called polyethylene terephthalate) belongs to, do occur in nature.

"They protect plant leaves," explained the University of Portsmouth researcher. "Bacteria have been evolving for millions of years to eat that."

The switch to PET was never the less "quite unexpected" and an international team of scientists set out to determine how the PETase enzyme had evolved.

Eating plastic

A high definition 3D model of the enzyme was created, using the powerful x-ray beamline at Diamond Light Source in Oxfordshire.

Once they understood its structure, the team noted that they could improve the performance of PETase by adjusting a few residues on its surface.

This suggests that the natural enzyme is not fully optimized yet and there is the potential to engineer it.

Closing the loop

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