A new scientific approach that alters a single atom in enzymes designed to break down plastics could significantly boost their efficiency while preserving their stability, according to research from The Australian National University, published in Angewandte Chemie International Edition. The study shows that making precise, single-atom modifications to highly engineered enzymes can enhance their ability to break down polyethylene terephthalate (PET)—a common plastic used in bottles and packaging—without reducing their stability. This development could address a key challenge in enzyme engineering, where improving performance often comes at the cost of structural integrity. The researchers focused on PET hydrolases, or PETases, which are naturally occurring enzymes capable of breaking down PET into smaller molecules. These enzymes have already been optimized through computational design and protein engineering. In this study, the team introduced a special type of amino acid called azatryptophan, which is nearly identical to the naturally occurring tryptophan, except that a carbon-hydrogen group is replaced with a nitrogen atom. By making this substitution at a single site in the enzyme, the researchers found that the modified enzymes could break down PET nearly twice as fast while maintaining their thermal stability. This approach challenges the conventional belief that enzyme engineering requires multiple changes to achieve improvements in function. To support their findings, the researchers also developed a new rapid test called PETra, which uses fluorescence to measure the activity of PET-degrading enzymes. Unlike traditional methods that can take hours or days, PETra provides results in minutes. The test uses a soluble fluorescent compound that mimics PET, allowing scientists to assess enzyme activity quickly. The results from PETra closely match how effectively the enzymes break down real PET, making it a valuable tool for rapidly screening future enzyme variants. The implications of this research extend beyond plastic recycling. Co-author Professor Thomas Huber noted that the method could be applied to a wide range of protein engineering efforts. By introducing noncanonical amino acids—those not found naturally in proteins—researchers can make very precise chemical changes that allow for fine-tuning of protein functions. This approach could have applications in sustainable manufacturing, biotechnology, and even medicine, opening new possibilities for designing enzymes with tailored properties.