A sea anemone known as strawberry anemone (Actinia fragacea) has been the basis for the development of artificial proteins capable of degrading small fragments (microplastics) of polyethylene terephthalate (PET, one of the most used plastics, present in many containers). and bottles) so that they are reduced to their essential components, which would allow their decomposition or recycling.
The new system for "deconstruction" of microplastics has been designed by scientists from the Institute of Catalysis and Petroleochemistry of the CSIC (ICP-CSIC), the Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS) and the Complutense University of Madrid (UCM ). The journal Nature Catalysis has published (October 19) the results of this research.
Every year about 400 million tons of plastics are produced in the world, a figure that increases by around 4% annually. The emissions that result from its manufacturing are one of the elements that contribute to climate change, and its ubiquitous presence in ecosystems entails serious ecological problems, recalls the CSIC in a note disclosing the results of the new study.
PET or polyethylene terephthalate wears out over time, forming increasingly smaller particles—so-called microplastics—which aggravates environmental problems. PET already accounts for more than 10% of global plastic production and its recycling is scarce and inefficient.
“What we do is something like adding new complements to a multipurpose tool to provide it with other different functionalities,” explains Víctor Guallar, ICREA professor at the BSC-CNS and one of those responsible for the work. These supplements consist of just three amino acids that function like scissors capable of cutting small PET particles. In this case, they have been added to a protein from the anemone Actinia fragacea, which in principle lacks this function and which in nature “functions like a cellular drill, opening pores and acting as a defense mechanism,” explains the researcher.
The machine learning and supercomputers used in this protein engineering allow us to “predict where the particles are going to join and where we must place the new amino acids so that they can exert their action,” Guallar summarizes. The resulting geometry is quite similar to that of the PETase enzyme from the bacteria Idionella sakaiensis, capable of degrading this type of plastic and discovered in 2016 in a packaging recycling plant in Japan.
The results indicate that the new protein is capable of degrading PET micro- and nanoplastics with “an efficiency between 5 and 10 times higher than that of the PETases currently on the market and at room temperature,” explains Guallar.
Other approaches require acting at temperatures above 70 °C to make the plastic more moldable, which entails high CO₂ emissions and limits its applicability. Furthermore, the pore-shaped structure of the protein was chosen because it allows water to pass through its interior and because it can be anchored to membranes similar to those used in desalination plants. This would facilitate their use in the form of filters, which “could be used in purification plants to degrade those particles that we do not see, but that are very difficult to eliminate and that we ingest,” highlights Manuel Ferrer, CSIC researcher at the ICP-CSIC and another of the study coordinators.
Another advantage of the new protein is that two variants were designed, depending on the places where the new amino acids are placed. The result is that each of them gives rise to different products. “A variant decomposes PET particles more exhaustively, so it could be used for degradation in treatment plants. The other gives rise to the initial components needed for recycling. In this way we can purify or recycle, depending on the needs,” explains Laura Fernández López, who is carrying out her doctoral thesis at the Institute of Catalysis and Petroleochemistry of the CSIC (ICP-CSIC).
The current design could already have applications, according to the researchers, but the flexibility of the protein—which they compare to a “multipurpose tool”—would allow new elements and combinations to be added and tested, explains Dr. Sara García Linares, from the University Complutense of Madrid. “What we are looking for is to combine the potential of the proteins that nature gives us and machine learning with supercomputers to produce new designs that allow us to achieve a healthy environment with zero plastics,” summarizes Ferrer.
“Computational methods and biotechnology can allow us to find solutions to many of the ecological problems that affect us,” concludes Professor Guallar.
Roberto Rosal, professor of Chemical Engineering at the University of Alcalá, explained in statements published by SMC Spain that the "interesting study" now published in Nature Catalysis describes "the preparation of a hydrolytic enzyme from mutants of fragacetoxin C of the sea anemone redesigned using computational methods".
"The result obtained in this research is very relevant, since it demonstrates the possibility of using genetic modifications to convert membrane pores into enzymes capable of addressing a reaction of industrial interest. The results of the proof of concept described in the work are very promising , and consisted of the degradation of poly(ethylene terephthalate) nanoparticles of about 100 nanometers in diameter to give rise to a variety of oligomers and depolymerized monomers that should be metabolizable by microorganisms," highlights Professor Roberto Rosal.
