SUSTAINABILITY AND THE ENVIRONMENT
Enzymes herald nature-based clean-up
Scientists who helped pioneer the use of enzymes to ‘ digest ’ plastic have taken an important next step in developing nature-based solutions to the global plastics waste crisis .
They have characterised an enzyme that has the capacity to help break down terephthalate ( TPA ), one of the chemical building blocks of PET plastic . PET plastic is used to make single-use drink bottles , clothing and synthetic carpets .
The latest research has been co-led by Professor Jennifer DuBois , Montana State University ( MSU ), and Professor John McGeehan , inaugral Director of the University of Portsmouth ’ s Centre for Enzyme Innovation .
It was Professor McGeehan who in 2018 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 , TPA and ethylene glycol ( EG ).
Now researchers have found an enzyme , called TPADO , that can break down TPA – further strengthening the potential for natural agents to biodegrade some of the most problematic plastics .
Professor DuBois explains the TPA / EG / PET relationship : “ 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 .
“ However , the Portsmouth team revealed that one of the PET-consuming enzymes , called TPADO , recognises the TPA chemical .
“ Our group at MSU then demonstrated that this enzyme breaks down TPA and pretty much only TPA , with amazing efficiency .”
Natural chemicals resource
It is anticipated that this research will open the way to the development of biological systems that can convert waste plastic into potentially useful by-products or natural chemicals with which new fully recyclable plastics can be made .
Researchers at the Centre for Enyme Innovation say the past few years have seen incredible advances in the engineering of enzymes to break down PET plastic into its building blocks :
“ Our new 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 , potentially making valuable products out of plastic waste .”
Using powerful X-ray technology at the Diamond Light Source – the UK ’ s national synchrotron science facility in Oxfordshire – Portsmouth ’ s team was able to generate a detailed 3D structure of the TPADO enzyme .
From this structure , the researchers can better understand how TPADO can break down the TPA molecules , and it has given researchers a blueprint for engineering faster and more efficient versions of this complex enzyme .
The healthy economics of an enzyme diet
While enzymes offer potential for a lowenergy solution to recycling some of the most commonly polluting single-use plastics and textiles , the global uptake of enzyme technology will be driven largely by cost .
To assess this , scientists in the UK and US , as part of the BOTTLE Consortium ( bottle . org ), have modelled a conceptual recycling facility where waste PET plastic is broken down with enzymes , returning the material into its original chemical building blocks . They have compared this with
28 ISSUE 04 / 2022