Researchers at the Australian National University have doubled the breakdown speed of a plastic-degrading enzyme by swapping a single atom in its molecular structure without sacrificing thermal stability.
The study focused on polyethylene terephthalate, commonly known as PET, which is one of the most widely used plastics globally and forms the primary component of consumer beverage bottles and food packaging.
Polyethylene terephthalate is a petroleum-based synthetic polymer engineered for high durability, structural strength, and moisture resistance. While mechanical recycling processes re-melt clear PET containers, biological recycling utilizes specialized proteins known as PETase enzymes to break down the complex polymer chains back into basic chemical monomers.
Biological recycling methods have long struggled to achieve industrial viability because natural enzymes capable of breaking down PET operate slowly and often lose their structural integrity when subjected to demanding processing conditions.
Enzymes are specialized protein molecules whose catalytic activity depends on maintaining precise three-dimensional structures. In industrial recycling systems, higher operating temperatures are required to soften dense plastic materials, but excessive heat frequently causes enzyme denaturation, causing standard proteins to unravel and lose function.
Single atom modification in protein structure
Rather than introducing extensive structural alterations throughout the protein, the Australian research team targeted a single minor chemical change. The investigators replaced the naturally occurring amino acid tryptophan with a synthetic variant called azatryptophan.
The structural difference between the two chemical compounds is extraordinarily minor. In the molecular configuration of azatryptophan, a carbon and hydrogen group is replaced by a single nitrogen atom.
Amino acids serve as the fundamental organic building blocks that fold into functional protein structures. Substituting standard amino acids with synthetic analogues enables bioengineers to adjust local chemical reactivity and bond strength without disrupting the overall architecture of the enzyme.
The single nitrogen substitution enabled the modified PETase enzyme to degrade solid PET at approximately double the speed of the original enzyme while retaining a substantial portion of its thermal stability under heat.
Fluorescence assay method for testing
Evaluating PET degradation under experimental conditions presents significant technical challenges because solid plastic breaks down slowly, forcing traditional laboratory trials to extend over several days.
To overcome this analytical hurdle, the researchers developed an innovative testing protocol named PETra. The system relies on fluorescence technology and uses a soluble chemical compound as a functional substitute for solid plastic during experimental trials.
Fluorescence spectroscopy measures the emission of light from molecules that have absorbed energy. When enzymatic breakdown occurs in the PETra assay, the reaction generates a light signal that allows researchers to measure enzymatic activity in real time.
Environmental impact and protein engineering
The research addresses an escalating environmental issue caused by the massive global volume of plastic waste generated each year. PET represents a major fraction of post-consumer waste, and existing management systems fail to process all discarded containers.
Although commercial recycling facilities operate worldwide, substantial volumes of PET plastic continue to end up in landfills or undergo thermal processing that can release toxic pollutants into the environment.
The research, published in the scientific journal Angewandte Chemie International Edition, highlights a promising direction for future protein engineering. The findings demonstrate that achieving significant performance gains in biological catalysts does not require altering an entire molecule, but rather knowing precisely which atom to modify.
