Enzyme Cocktail

In 2018, University of Portsmouth’s Professor John McGeehan and colleagues engineered an enzyme that can digest polyethylene terephthalate (PET), the primary material used in the manufacture of single-use plastic beverage bottles. Now, the same team has created a two-enzyme cocktail that can digest PET up to six times faster.

Knott et al. created a two-enzyme system for PET deconstruction, which employs one enzyme (PETase) to convert the polymer into soluble intermediates and another enzyme (MHETase) to produce the constituent PET monomers. This SEM image shows amorphous PET film after 96 h enzyme treatment at 30 degrees Celsius. Image credit: Knott et al., doi: 10.1073/pnas.2006753117.

Knott et al. created a two-enzyme system for PET deconstruction, which employs one enzyme (PETase) to convert the polymer into soluble intermediates and another enzyme (MHETase) to produce the constituent PET monomers. This SEM image shows amorphous PET film after 96 h enzyme treatment at 30 degrees Celsius. Image credit: Knott et al., doi: 10.1073/pnas.2006753117.

Plastics pollution represents a global environmental crisis. In response, microbes are evolving the capacity to utilize synthetic polymers as carbon and energy sources.

In 2016, a team of Japanese biologists reported the discovery and characterization of the soil bacterium, Ideonella sakaiensis 201-F6, which uses two enzymes to depolymerize PET to its constituent monomers.

Further characterization of Ideonella sakaiensis revealed a PET-degrading called PETase.

The discovery heralded the first hope that a solution to the global plastic pollution problem might be within grasp, though PETase alone is not yet fast enough to make the process commercially viable to handle the tons of discarded PET bottles littering the planet.

In 2018, Professor McGeehan and co-authors studied the structure of the PETase enzyme and engineered it in the lab to be around 20% faster at breaking down PET.

In the new study, they combined PETase and a second enzyme called MHETase, found in the soil bacterium, to generate a two-enzyme system for PET deconstruction.

MHETase structural analysis. Image credit: Knott et al., doi: 10.1073/pnas.2006753117.

MHETase structural analysis. Image credit: Knott et al., doi: 10.1073/pnas.2006753117.

“We were chatting about how PETase attacks the surface of the plastics and MHETase chops things up further, so it seemed natural to see if we could use them together, mimicking what happens in nature,” Professor McGeehan said.

“Our first experiments showed that they did indeed work better together, so we decided to try to physically link them, like two Pac-men joined by a piece of string.”

“We were delighted to see that our new chimeric enzyme is up to three times faster than the naturally evolved separate enzymes, opening new avenues for further improvements.”

The researchers studied the 3D structure of the MHETase enzyme, giving them the molecular blueprints to begin engineering a faster enzyme system.

They used the Diamond Light Source, a synchrotron that uses intense beams of X-rays 10 billion times brighter than the Sun, to act as a microscope powerful enough to see individual atoms.

“Our research combined structural, computational, biochemical and bioinformatics approaches to reveal molecular insights into its structure and how it functions,” they said.

“The study was a huge team effort involving scientists at all levels of their careers.”

The findings were published in the Proceedings of the National Academy of Sciences.

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Brandon C. Knott et al. Characterization and engineering of a two-enzyme system for plastics depolymerization. PNAS, published online September 28, 2020; doi: 10.1073/pnas.2006753117

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