Engineered enzyme able to break down PET in ten hours

Engineered enzyme able to break down PET in ten hours
a, Structural model of 2-HE(MHET)3 (coloured stick model) docked in wild-type LCC (grey ribbon). The putative substrate-binding site of LCC can be subdivided into three subsites (−2, −1, +1), each in contact with the MHET units numbered relative to the scissile ester bond (red triangles). Amino acids in the first contact shell of LCC are shown as grey rods. Catalytic residues are in magenta. b, Calculated percentage improvement in specific activity of Pf-PET depolymerization by the F243I and F243W variants compared with wild-type LCC at 65 °C (6.9 nmolprotein gPET−1 and 2 gPET lbuffer−1). Means ± s.d. (n = 3) are shown; *P < 0.025; **P < 0.005 (one-sided t-test). Credit: Nature (2020). DOI: 10.1038/s41586-020-2149-4

A team of researchers from TBI, Université de Toulouse, CRITT Bio-Industries and Carbios, Biopôle Clermont Limagne, has engineered a commonly known enzyme to efficiently break the chains that hold the building blocks of polyethylene terephthalate (PET) together. In their paper published in the journal Nature, the group describes how they developed the enzyme and how well it worked in a test plant.

PET is a very of plastic used in products from soda bottles to —it is also the source of a lot of trash. Despite efforts by consumers to recycle such materials, the ability of recyclers to tear them down into their basic parts for reuse is quite limited. Until now, processes that have been used to break the bonds holding PET monomers together have been inefficient—just 30 percent of the materials are reused. In this new effort, the researchers have engineered an known to break down plastic for higher efficiency.

The leaf-branch compost cutinase enzyme, as its name suggests, is an enzyme found in nature that is able to break the bonds that hold leaves together, making them digestible. Prior research has shown that they are able to do the same with PET, but very inefficiently. The team began their work by taking a closer look at the enzyme looking specifically for the key amino acids that were used to bind to the linkers holding PET monomers together. They then created hundreds of mutant enzymes with different amino acid properties.

Next, they tested the mutants on their munching abilities. After much effort, the were able to find and isolate the mutant that worked best—they found it to be 10,000 times more efficient at cutting PET bonds than the native enzyme. The team then mass-produced batches of the mutant enzyme and placed them in a reactor for testing. They found that the enzyme they had created was capable of breaking down 200 grams of PET in just 10 hours—and that it was 90 percent efficient. They then used the broken-down material generated by the enzyme to create new PET, and found that it was just as strong as those that had been recycled. The team plans to build a larger reactor to prove that the process is economically viable.


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Improving nature's tools for digesting plastic

More information: V. Tournier et al. An engineered PET depolymerase to break down and recycle plastic bottles, Nature (2020). DOI: 10.1038/s41586-020-2149-4
Journal information: Nature

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Citation: Engineered enzyme able to break down PET in ten hours (2020, April 9) retrieved 28 May 2020 from https://phys.org/news/2020-04-enzyme-pet-ten-hours.html
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