Researchers at the Manchester Institute of Biotechnology (MIB) have developed a novel enzyme engineering platform to improve plastic degradation enzymes through directed evolution.
To illustrate the usefulness of their platform, they designed an enzyme capable of successfully degrading poly(ethylene) terephthalate (PET), the plastic commonly used in plastic bottles.
In recent years, enzymatic recycling of plastics has emerged as an attractive and environmentally friendly strategy to help alleviate the problems associated with plastic waste. Although there are a number of methods for recycling plastics, enzymes could potentially offer a more cost effective and energy efficient alternative. Additionally, they could be used to selectively break down specific components of mixed plastic waste streams that are currently difficult to recycle using existing technologies.
Although promising as a technology, considerable hurdles must be overcome for enzymatic plastic recycling to be widely used on a commercial scale. One challenge, for example, is that natural enzymes capable of breaking down plastics are generally less efficient and unstable under the conditions needed for an industrial-scale process.
To address these limitations, in an article published today in Nature Catalysis, Researchers from the University of Manchester have presented a new enzyme engineering platform capable of rapidly improving the properties of plastic-degrading enzymes to make them more suitable for large-scale plastic recycling. Their integrated and automated platform can successfully assess the plastic degradation capacity of approximately 1000 enzyme variants per day.
Dr. Elizabeth Bell, who led the experimental work at MIB, said of the platform; “The accumulation of plastic in the environment is a major global challenge. For this reason, we wanted to use our enzyme evolution capabilities to improve the properties of plastic degrading enzymes to help alleviate some of these issues. We hope that in the future our scalable platform will allow us to rapidly develop new specific enzymes suitable for use in large-scale plastic recycling processes. »
To test their platform, they then developed a new enzyme, HotPETase, via directed evolution of IsPETase. IsPETase is a recently discovered enzyme produced by the bacterium Ideonella sakaiensis, which can use PET as a source of carbon and energy.
Although IsPETase has the natural ability to degrade certain semi-crystalline forms of PET, the enzyme is unstable at temperatures above 40°C, well below desirable processing conditions. This low stability means that reactions must be performed at temperatures below the glass transition temperature of PET (~65°C), which leads to low rates of depolymerization.
To overcome this limitation, the team developed a thermostable enzyme, HotPETase, which is active at 70°C, which is above the glass transition temperature of PET. This enzyme can depolymerize semi-crystalline PET faster than previously reported enzymes and can selectively deconstruct the PET component of a laminated packaging material, highlighting the selectivity that can be achieved by enzymatic recycling.
Professor Anthony Green, Lecturer in Organic Chemistry, said: “The development of HotPETase exemplifies 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. we hope that our platform will prove useful in developing more efficient, stable and selective enzymes for recycling a wide range of plastic materials. »
The development of robust plastic degrading enzymes such as HotPETase, together with the availability of a versatile enzyme engineering platform, are making important contributions to the development of a biotechnological solution to the plastic waste challenge. Moving this promising technology forward will now require a collaborative, multidisciplinary effort involving biotechnologists, process engineers, and polymer scientists from across academic and industrial communities. As the world faces a growing waste problem, biotechnology could provide an environmentally sustainable solution.