Enzyme MHETase decoded
Plastics are excellent materials: extremely versatile and almost eternally durable. But this is also exactly the problem, because after only about 100 years of producing plastics, plastic particles are now found everywhere – in groundwater, in the oceans, in the air, and in the food chain. Around 50 million tonnes of the industrially important polymer PET are produced every year. Just a tiny fraction of plastics is currently recycled at all by expensive and energy-consuming processes which yield either downgraded products or depend in turn on adding ‘fresh’ crude oil.
In 2016, a group of Japanese researchers has discovered a bacterium that grows on PET and partially feeds on it. They found out that his bacterium possesses two special enzymes, PETase and MHETase, which are able to digest PET plastic polymers. PETase breaks down the plastic into smaller PET building blocks, primarily MHET, and MHETase splits this into the two basic precursor building blocks of PET, terephthalic acid and ethylene glycol. Both components are very valuable for synthesising new PET without the addition of crude oil – for a closed sustainable production and recovery cycle.
In April 2018, the structure of PETase was finally solved independently by several research groups, the Diamond Light Source was also involved in the experiments. However, PETase is only part of the solution. It is equally important to characterize the structure of the second enzyme, MHETase.