Specially-evolved enzyme degrades problematic packaging

A new ‘enzyme engineering platform’ has been designed by researchers from the Manchester Institute of Biotechnology (MIB), resulting in the development of an enzyme that can selectively degrade polyethylene terephthalate (PET), commonly used for plastic bottles.

The platform aims to address the commercial limitations of natural enzymes, with the researchers’ paper – published in Nature Catalysis – noting these enzymes are unstable and less effective under industrial conditions. These enzymes can be quickly improved through MIB’s platform, altering their properties to make them more suitable for plastic recycling at large scales. At present, the platform can assess the plastic degradation ability of around 1,000 enzyme variants each day using robots.

‘Natural evolution, but on a laboratory scale’

The researchers at MIB took an enzyme called IsPETase, able to use PET as a carbon and energy source, and, through ‘directed evolution’, created a new enzyme – HotPETase. The resulting enzyme was developed by the researchers with PET specifically in mind, and is able to selectively break down the PET portion of mixed-material film lids.

Multi-material packaging – where different plastics and other materials are bonded together – is particularly challenging for mechanical recycling, with these materials often sent to landfill or incinerated as a result. MIB’s evolved enzymes present a solution, selectively breaking down specific parts of the packaging and leaving the rest to be recycled mechanically.

MIB described the development process as ‘natural evolution, but on a laboratory scale’ – the researchers selected specific parts of the enzyme that were important for catalysis, mutating them to see if the resulting variants had a better ability to degrade PET.

The process managed to overcome issues with the original enzyme – IsPETase is unstable at temperatures above 40C , whereas the evolved HotPETase is thermostable at 70C. HotPETase also degrades semi-crystalline PET more rapidly than previous enzymes, without the need for an energy-intensive plastic pre-processing stage.

The enzyme still has space for improvement, though. HotPETase is currently only active for around eight hours, with MIB noting that use in industrial processes would require more stability, so the enzyme ‘can react for longer periods’. However, this is already a ‘great starting point’ – the researchers are well on their way to developing an industrial standard PEtase.

Looking ahead, MIB said that it will be using the platform to develop other enzymes ‘specific for other types of plastics’, with scope for collaboration with other scientists on how these enzymes might look and act.

Dr Elizabeth Bell, who led the experimental work at the MIB, said: “The accumulation of plastic in the environment is a major global challenge. For this reason, we were keen to use our enzyme evolution capabilities to enhance the properties of plastic degrading enzymes to help alleviate some of these problems. 

“We are hopeful that in the future our scalable platform will allow us to quickly develop new and specific enzymes are suitable for use in large-scale plastic recycling processes.

Professor Anthony Green, Lecturer in Organic Chemistry, added: “The development of HotPETase nicely illustrates the capabilities of our enzyme engineering platform. We are now excited to work with process engineers and polymer scientists to test our enzyme in real world applications.

“Moving forward, we are hopeful that our platform will prove useful for developing more efficient, stable, and selective enzymes for recycling a wide range of plastic materials.”