New enzyme technology for environmentally friendly plastic recycling

Drone shot of a landfill with a lot of plastic waste in Indonesia.

Co-Authors: Martin Walpot & Doris Ribitsch

An enzyme called tyrosinase, which is responsible for triggering a protective mechanism in plants and turning apples brown, even possesses further, previously unknown properties: For the first time, acib researchers have used the proteolytic abilities of tyrosinases to improve another enzyme – so that it can degrade plastic.

The paradigm “one enzyme – one function” valid for many decades, has changed dramatically in the past years. Technical achievements like genome sequencing revealed that actually only a limited number of enzymes catalyses hundred thousands of reactions in a cell. One approach how nature deals with the disproportion between enzymes and biochemical reactions is the usage of so called “multifunctional enzymes”. Multifunctional enzymes are proteins that perform at least two distinct enzymatic activities whereby the different substrates might be bound in one or more active sites. In vivo, the multifunctionality allows enzymes to play multiple physiological roles whereas in vitro, multifunctional enzymes became interesting biocatalysts for industrial biotransformations.

Understanding the roles of multifunctional enzymes

For this reason, comprehensive investigation of multifunctional proteins and enzymes in particular became highly important in order to understand their roles in complex biochemical pathways but also to develop novel biocatalysts for future industrial applications. Very recently, acib-researchers in Tulln have been able to explore the enzyme promiscuity of tyrosinases by using modern chromatography, crystallography and mass spectrometry methods and answer numerous questions: How does the new mechanism proceed? Where do these second functions or secondary activities come from? Why do unexpected reaction products occur? And what are they?

Tyrosinases of interest for biotechnological applications

acib researchers could describe for the very first time the cleavage of a full-length protein (EstA) by the investigated tyrosinase. Through this cleavage a truncated version of EstA became available which shows drastically increases activity towards the degradation of the synthetic polymer polyethylene terephthalate (PET), commonly used in plastic bottles.

With this increased knowledge regarding tyrosinases, it may soon be possible to find a way to exploit the specific “multitasking properties” of these enzymes for different biotechnological applications. For example, the information gained about functional changes for the gene sequences could be used for industrial applications of promiscuous enzymes in biotechnological fields such as enzymology, chemical biology, food industry, and for state-of-the-art directed evolution techniques. For example, these enzymes can be used by industry to break down synthetic polyesters and non-degradable PET into its individual components.

The results of the acib and University of Vienna researchers were recently published in the Nature journal Communications Chemistry.

This article is based on: A. Biundo, V. Braunschmid, M. Pretzler, I. Kampatsikas, B. Darnhofer, R. Birner-Grünberger, A. Rompel, D. Ribitsch, GM Gübitz: Polyphenol oxidases exhibit promiscuous proteolytic activity. Nature communications chemistry, 2020, 3 (62).

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