The scientists who helped to pioneer the use of enzymes to eat plastic have characterised an enzyme that has a remarkable capacity for breaking down terephthalate (TPA), one of the chemical building blocks of polyethylene terephthalate (PET) plastic, which is used to make single-use drinks bottles, clothing and carpets.
The research was co-led by Professor Jen DuBois of Montana State University and Professor John McGeehan of the University of Portsmouth, who led the international team that engineered a natural enzyme that could break down PET plastic. The enzymes (PETase and MHETase) break the PET polymer into the chemical building blocks ethylene glycol (EG) and TPA. The new research describes the next step – specifically for managing TPA.
‘While EG is a chemical with many uses – it’s part of the antifreeze you put into your car, for example – TPA does not have many uses outside of PET, nor is it something that most bacteria can even digest,’ said DuBois. ‘However, the Portsmouth team revealed that an enzyme from PET-consuming bacteria recognises TPA like a hand in a glove. Our group at MSU then demonstrated that this enzyme, called TPADO, breaks down TPA and pretty much only TPA, with amazing efficiency.’
The researchers hope that the new discovery will open the door to improvements to bacterial enzymes such as TPADO, helping to tackle the challenge of plastic pollution and develop biological systems that can convert waste plastic into valuable products.
‘The last few years have seen incredible advances in the engineering of enzymes to break down PET plastic into its building blocks,’ said McGeehan, who is the director of Portsmouth University’s Centre for Enzyme Innovation. ‘This work goes a stage further and looks at the first enzyme in a cascade that can deconstruct those building blocks into simpler molecules. These can then be utilised by bacteria to generate sustainable chemicals and materials, essential making valuable products out of plastic waste.
‘Using a powerful X-ray at the Diamond Light Source, we were able to generate a detailed 3D structure of the TPADO enzyme, revealing how it performs this crucial reaction,’ he continued. ‘This provides researchers with a blueprint for engineering faster and more efficient versions of this complex enzyme.’
The research has been published in the Proceedings of the National Academy of Sciences.