Enzymes for bioplastics synthesis and recycling

Plastics are versatile materials with a multitude of applications in our daily lives, some of which provide very beneficial solutions for our society that we can hardly do without. However, the plastics industry is currently in the spotlight mainly due to the petrochemical origin of its raw materials, the traditionally linear approach to its manufacture (take-make-waste), and the associated management of the generated waste, with the consequent environmental impact that all this entails.

Due to their huge production volume, plastics have become a key strategic priority within the EU Circular Economy Action Plan, with a particular focus on their production, use, and recycling systems. Similarly, addressing solutions to achieve a more sustainable plastics industry in Europe, in terms of reducing emissions as well as reducing and/or reusing its waste, is key to meeting the objectives of the European Green Deal. One of the most promising strategies is substituting fossil-based materials with others of renewable origin to produce bioplastics with a lower carbon footprint than traditional plastics while obtaining recyclable products aimed to improve the circularity of the processes. In this context, the use of enzymatic biocatalysts is a state-of-the-art technology that can contribute to the industrial and environmental viability of bioplastics, facilitating the synthesis and recycling of their precursors and polymers.

One of the most widely used plastic materials in beverage and food packaging is PET, a polyester of petrochemical origin. Its most promising bio-based alternative is PEF, whose precursor can be obtained from biomass sugars through a series of oxidative transformations. Currently, there already exist "oxidase" enzymes capable of catalyzing these transformations as a more selective and environmentally friendly alternative to available chemical methods. On the other hand, it is possible to design "esterase" type hydrolytic enzymes to catalyze specific depolymerization reactions of PEF and related polymers, allowing the recycling of their precursors to obtain new materials.

Despite this potential, some of the most relevant enzymes known to catalyze this type of reaction evolved to act on natural substrates, so optimizing them to oxidize or hydrolyze plastic synthetic compounds is necessary. In the collaborative project FURENPOL, coordinated by the Group of Biotechnology for Lignocellulosic Biomass of CIB Margarita Salas and involving six other Spanish partners, different strategies are being investigated to improve the properties of these biocatalysts through protein engineering. Thanks to the use of advanced software developed by the consortium members, we can explore tens of thousands of sequences in databases, perform extensive computational simulations on the access, accommodation, and reaction of substrates in the enzyme active site, and make predictions based on machine learning and other techniques. These analyses provide us with a series of potentially better candidates, which are evaluated experimentally in the laboratory to verify that they actually present improved performances for the reactions of interest than the known enzymes. Another objective of the project is to increase the production of the best biocatalysts using fermentation and process intensification technologies and optimize the enzymatic reactions to obtain and recycle PEF-type biopolymers. Finally, the polymers obtained will be evaluated in various applications within the framework of the project. By using optimized enzymes and bioprocesses for the biosynthesis and depolymerization of these bioplastics, we expect to achieve industrial and environmental improvements relevant to the plastics sector.

FURENPOL brings together the necessary actors to complete these studies, in a consortium that includes representatives of Research and Industry from the Biotechnology and Plastics sectors. The project is funded by the State Research Agency with NextGenerationEU funds, answering to the thematic priority "Sustainability of plastics: synthesis, recycling, and valorization" of the 2021 call for projects in Strategic Lines. In addition, FURENPOL is part of the portfolio of projects included in the CSIC interdisciplinary thematic platform on sustainable plastics, SusPlast, with the participation of several members of the consortium.

FurEnPol (Furanic Enzymatic Polymers): “Enzymatic Synthesis and Recycling of Biobased Furanic Polymers”, Project PLEC2021-007690 funded by MCIN/AEI/10.13039/501100011033 y and by the European Union NextGenerationEU/PRTR