17. April 2019 | Recycling

Molecular scissors for plastic waste

MHET-Moleküle aus PET-Kunststoff docken an einer aktiven Stelle im Inneren der MHETase an und werden dort aufgespalten
MHET molecules made of PET plastic dock at an active site inside the MHETase and are split there
Source: M. Künsting/HZB

According to a publication in the Open Access journal Nature Communications, a team from the University of Greifswald and the Helmholtz-Zentrum Berlin, both Germany, has now deciphered the structure of an important enzyme (MHETase). The 3D structure of MHETase reportedly has enabled the researchers to specifically optimize the activity of this enzyme. According to the research team, it is now possible to use it for sustainable PET recycling without using oil.

Discovered in 2016

A group of Japanese researchers discovered a bacterium that can grow on PET plastics and partially feed on them in 2016. This bacterium consists of two special enzymes that are able to degrade PET plastic: PETase and MHETase. The first enzyme converts the plastic into mainly the smaller MHET. Then MHETase is converted to the two basic PET components, terephthalate and ethylene glycol.

Deciphering both enzymes

Since plastic waste is produced faster than the bacterium can adapt to evolutionary changes, the structural decoding of enzymes is of particular importance. In April 2018, several research groups succeeded in clarifying the structure of the enzyme PETase. Now, one year later, the larger and more complex MHETase has been deciphered.

"After clarifying the structure of this very important enzyme, we are now able to plan, produce and biochemically characterize variants that show considerably higher activity than the natural MHETase," explained Prof. Dr. Uwe Bornscheuer from the Institute of Biochemistry at the University of Greifswald.

Genuine closed-loop economy

In the future, PETase and MHETase will be systematically optimized for their task of dismantling PET. In the future, such optimized enzymes could be produced in closed biotechnological cycles in order to decompose PET plastics and (in perspective) other polymers into their basic components. Provided that waste is separated, the production of plastics would then be a closed cycle.

edited by Thobias Quaß

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