Design an enzyme that digests plastic bottles

Scientists have designed an enzyme that can digest some of the plastics most commonly pollutants, providing a potential solution to one of the greatest environmental problems of the world. The research, published this week in the Proceedings of the National Academy of Sciences, was led by teams from the University of Portsmouth, Uk, and the National Renewable Energy Laboratory (NREL, for its acronym in English) of the Department of Energy, united States.

Professor John McGeehan, University of Portsmouth, and dr. Gregg Beckham, NREL, solved the crystal structure of PETase, an enzyme recently discovered that digests the PET, and used this information in 3D to understand how it works. During this study, designed involuntarily, an enzyme that is even better to degrade the plastic that develops in nature.

The researchers are now working on the improvement of the enzyme to allow its industrial use to break down the plastic in less time. “Few could have predicted that, given that the plastics became popular in the 1960s, enormous patches of plastic would be found floating in the oceans, or will collapse in the beaches, once pristine in the entire world,” laments the professor McGeehan, director of the Institute of Biological and Biomedical Sciences, Faculty of Biological Sciences, Portsmouth.

For the researcher, all the world can play an important role in the treatment of the problem of the plastic, but it is the scientific community that ultimately created these “wonderful materials” that must now “use all the technology at their disposal to develop real solutions“.

The researchers made the breakthrough when they were discussing the structure of a natural enzyme that is thought to be developed in a centre of recycling of waste in Japan, allowing a bacterium to degrade the plastic as a food source.

The PET, patented as a plastic in the 1940s, it has not existed in the nature for a long time, so the team set out to determine how evolved the enzyme and if it is possible to improve it. The goal was to determine their structure, but they ended up going a step further and designed accidentally an enzyme that it was even better to break down the plastic of PET.

To a solution of recycling

“Chance often plays an important role in basic scientific research and our discovery here is not an exception,” says professor McGeehan. “Although the improvement is modest, this unexpected discovery suggests that there is room to further improve these enzymes, bringing us closer to a recycling solution for the ever increasing mountain of plastic waste, “he adds.

The research team now you can apply the tools of protein engineering and evolution to continue to improve. The University of Portsmouth and NREL collaborated with scientists at the Diamond Light Source in Uk, a synchrotron that uses intense beams of X-rays 10,000 million times brighter than the sun to act as a microscope powerful enough to see individual atoms. Using his last laboratory, beamline I23, is generated in exquisite detail a 3D model of ultra-high resolution of the enzyme PETase.

Professor McGeehan explains that Diamond Light Source has recently started one of the lines of X-ray most advanced in the world and that the access to this installation allowed the scientists to see atomic structure in 3D PETase with incredible detail. “This biological catalyst provided us with the blueprints for designing an enzyme faster and more efficient,” he says.

The executive director of Diamond Light Source, professor Andrew Harrison, points out that “with the contribution of five institutions in three different countries, this research is an excellent example of how international collaboration can help to achieve important scientific advances”.

“The detail that the team could extract from the results obtained at the beamline I23 at Diamond will be invaluable when trying to tailor the enzyme for use in recycling processes to large-scale industrial. The impact of a solution so innovative for the plastic waste, that would be fantastic. It is fantastic that the scientists and facilities of the Uk are helping to lead the way”, celebrates.

With the help of scientists from computational modeling of the University of South Florida, in the united States, and the state University of Campinas, in Brazil, the team discovered that PETase is very similar to a cutinase, but it has some unusual features, including an active site more open. These differences indicated that PETasa may have evolved in an environment that contains a PET scan to allow the enzyme to degrade the PET. To test this hypothesis, the researchers mutated the active site of PETase to make it more similar to a cutinase.

And it was then when the unexpected happened: the researchers found that the PETasa mutant was better than the PETasa natural to degrade PET. Significantly, the enzyme can also degrade the polyethylene furandicarboxilato, or PEF, a surrogate of the biological basis for PET plastics highly acclaimed as a replacement for beer bottles glass.

“The engineering process is very similar to the enzymes that are currently used in detergents to biolavado and in the manufacture of biofuels: the technology is there and it is likely that in the next few years let’s look at a process industrially viable to convert PET, and potentially other substrates such as PEF, PLA and PBS, back to their original building blocks so that they can be recycled in a sustainable way”, explains the professor McGeehan.

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