A group of scientists from the University of Texas have developed a modified enzyme that can break down plastic in days. Normally, it takes time for the plastic to completely decompose.
the results researchers were published last week in the scientific journal Nature† The study used machine learning to create mutations of a fast-acting protein that can break down the building blocks of polyethylene terephthalate (PET). PET is a synthetic resin used in fibers for clothing and plastic. According to the study, this substance is responsible for 12% of global waste.
The plastic has been broken down by a process called depolymerization. In this process, a catalyst separates the building blocks that make up PET into their original monomers, which are organic molecules. These monomers can then be repolymerized to create a new plastic, which can be incorporated into other products. The most impressive thing about this process is that enzymes can break down plastic within a week.
“We can break it down into its original monomers,” Hal Alper, professor of chemical engineering and author of the paper, told VICE by phone. “That’s what the enzyme does. And once you get that stock monomer, it’s like making fresh plastic from scratch, with the added benefit of not having to use any extra petroleum. »
“It has advantages over traditional recycling,” Alper added. “If you melted the plastic and then reshaped it, the plastic would lose its integrity each time you re-polymerize it. But if you’re able to chemically depolymerize and then repolymerize it, you can make new PET plastic every time.
Their work complements a series of existing studies on plastic-eating enzymes, first discovered in 2005. Since then, 19 more enzymes have been discovered, according to the article. These enzymes come from bacteria naturally present on the plastic.
Many of these natural enzymes are made up of advanced proteins that work well in their specific environment, but are limited by temperature and pH conditions. As a result, they can’t just be used in any setting, such as at recycling centers, the authors explain. In contrast, the enzyme discovered by Alper and his team can break down 51 types of PET under a range of temperature and pH conditions.
The researchers named the enzyme FAST-PETase, which is an acronym for “Functional, Active, Stable, and Tolerant PETase,” and they found the exact structure using machine learning. An algorithm was fed 19,000 protein structures and learned to predict the positions of amino acids in a structure. They also used the formula to rearrange the amino acids of existing PETase types into new positions, identifying improved amino acid combinations. The researchers arrived at a structure that showed 2.4 times more activity than an existing PETase enzyme at 40 degrees Celsius and 38 times more activity at 50 degrees Celsius.
It was then tested at different temperatures and pH levels, and it continued to perform well.
“What you see in nature is probably somewhat optimal, at least in the local environment around each of these amino acids,” Alper says. “We can start looking at the protein we’re interested in and then go through each of the amino acids. The microenvironment of these amino acids will clearly indicate what is suitable and what is not.
Alper and his team hope their enzyme will be more scalable than most and that PETase can really make a difference in tackling the global plastic crisis. FAST-PETase can handle a range of different conditions, but now needs to prove that it can be both “portable and affordable on an industrial scale”.
First, says Alper, he and his team need to test FAST-PETase on the many types of PET found in sewers. It should also be tested for trash commonly found in plastic bottles or on plastic packaging during the recycling process. If researchers find an enzyme or group of enzymes robust enough to be used in practice, they say it could helpbillions of tons” fight against waste in our environment.
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