Stopping the Spiral of Waste

DECTRIS helps clean up oceans. This might sound weird, as DECTRIS is a Swiss company that makes X-ray detectors; however, it's one way of interpreting a recent study that examined the structure and improved the activity of a plastic-degrading enzyme. Although many elements played a role in this success, the customer-specific PILATUS 12M-DLS detector at beamline I23 of Diamond Light Source was vital for solving the structure of the protein.

Armin Wagner in front of the PILATUS 12M-DLS detector

Principal beamline scientist Armin Wagner in front of the PILATUS 12M-DLS detector (courtesy of Diamond Light Source).

Polyethylene terephthalate (PET) is one of the most abundant plastics manufactured in the world due to its transparency, low weight, relative chemical inertness, and impermeability to liquids. It is mostly used for making single-use bottles and its crystalline form makes it resistant to catalytic depolymerization and thus effective recycling. It can persist in the environment for decades and perhaps centuries.

Although global PET recycling rates are well below 50%, even in green countries like Germany, India or Switzerland, an issue still remains: When PET is recycled, inferior forms of the plastic are produced. Recycled bottles become polyester sweaters as cloudless transparency cannot be guaranteed. Recycled sweaters in turn become carpets. It’s not so much recycling as a deadly downward spiral.

Discovery of PETase

A bacterium was discovered in 2015 which can grow on PET as its major source of carbon and energy. A secreted enzyme that catalyzes the depolyermization of PET is key to its lifestyle. This enzyme known as PETase cleaves PET to an intermediate product that a second secreted enzyme can additionally change into the substrates of PET synthesis, ethylene glycol, and terephthalic acid. If this biodegradation pathway could be implemented at an industrial level, efficient PET recycling might be feasible. This would help minimize pollution caused by PET and the squandering of oil to make more PET.

PILATUS 12M-DLS

PILATUS 12M-DLS custom-built for beamline I23 at Diamond Light Source.

Native SAD, a method that exploits minute variations in the intensities of related reflections, was used to solve the structure of PETase. Beamline I23 of Diamond Light Source was particularly built for this application. Thanks to the custom-designed PILATUS 12M-DLS detector that works in vacuum, the beamline ensures the most accurate data possible.

Look at the diffraction images, there's almost no background. The data quality is outstanding.

Armin Wagner, Principal Beamline Scientist, I23

Data was finally collected with a resolution better than 1 Å. At this level of detail, unusual in structural biology, distances between individual atoms can be determined with extreme accuracy, and the chemistry at the core of catalysis and substrate binding can be deduced with confidence. The comprehensive view of the enzyme’s active site provided researchers, headed by John McGeehan (University of Portsmouth) and including partners in Brazil, the US, and the UK, with a strong hypothesis of the way PET hydrolysis proceeds. With this information, targeted functional changes can be made and this is what the research team did next. Two slight alterations in the active site produced an enzyme with a considerably increased PET-degrading activity.

Conclusion

Currently, plastic waste is one of the grave ecological challenges. Although PET bottles seem innocent enough, they get pulverized by sunlight and mechanical stress and can enter the food chain – with incalculable outcomes for human health. Biotechnology holds the solution to this challenge. Harnessed industrially, the decomposition of PET into its components could possibly reshape the present spiral of waste into a continuous loop of recycling.

References

Additional information

This information has been sourced, reviewed and adapted from materials provided by Dectris Ltd.

For more information on this source, please visit Dectris Ltd.

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