Polyurethane degrading enzymes: Structural analysis and development.Tools Southwood, Callum (2025) Polyurethane degrading enzymes: Structural analysis and development. PhD thesis, University of Nottingham.
AbstractPlastics are a group of materials that, due to their highly desirable properties and low production costs, have become ubiquitous in daily lives across the globe. The term ‘Plastic’ is typically used to describe fully synthetic polymers derived largely from petrochemical monomers. Plastics tend to be extremely resistant to environmental and bacterial degradation, this is a very desirable material characteristic, but has led to their accumulation in the environment, where their longevity now poses a rapidly growing problem. Polyurethanes are just one type of these plastics that are contributing toward this growing plastic waste problem. Up to 6% of all plastic production is polyurethanes and current recycling methods for these materials are limited, meaning much of this material ends its life in landfill. The growing plastic waste problem has led to many developments in plastic waste management in recent years, one of which is a biological solution utilising enzymatic degradation. This novel solution aims to break down plastic waste into its constituent chemical monomers using enzymes. So far, much of the research and development has focused on enzymes capable of degrading poly(ethylene) terephthalate, however this study looks to shift this attention towards a polyurethane degrading enzyme and producing a viable recycling method. In this study, the in silico structural analysis of an insufficiently investigated polyurethane degrading enzyme elucidated a novel binding region. These insights were used to inform the rational design and development of a novel polyurethane degrading enzyme from a well characterised esterase with no previous plastic degrading capabilities. The resultant novel enzyme, EST2_Eng, was shown to degrade a commercially relevant polyurethane substrate at a similar level to current enzymes, with a mass loss of 0.7% in solid cubes and 4.5% mass loss in pretreated cubes. This was achieved at comparatively lower temperatures of 30°C. This not only shows that this binding region can confer polyurethane activity to other enzymes but also that it may provide a new route to a viable recycling process with lower energy requirements.
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