Discovery and Biochemical Characterization of a Novel Polyesterase for the Degradation of Synthetic Plastics

Since the beginning of the large-scale production of plastics in the 1950s, these materials have found a wide variety of applications and became essential in today’s society. Abandoned plastic waste poses an enormous environmental problem, contaminating the soil and oceans, due to the release of microplastics which are ingested by animals and end up in humans through food webs. Recent studies have highlighted the failure of traditional recycling processes thus new greener concepts and approaches have emerged, incorporating microorganisms and their enzymes for depolymerization of used plastics.

Studies dealing with the enzymatic degradation of synthetic polyesters have been performed for over 15 years. However, since 2016 the discussion about PET-degrading enzymes has bloomed. Turning point was the work of Yoshida et al, who discovered a PET-assimilating bacterium, namely Ideonella sakaiensis. The enzyme responsible for the degradation of the polymer was identified and named IsPETase. Till then, enzymes belonging to the family of cutinases had been studied for polyester degradation.

The present work aimed to the discovery of a novel polyester-degrading enzyme (polyesterase), using bioinformatics tools. The few known PET-degrading enzymes were used as templates for the identification of homologous sequences. The search led to a protein sequence originating from an Antarctic bacterium of the genus Moraxella sharing the highest similarity with IsPETase (45.2%), followed by actinomycete cutinases (41.48-46.05%). The recombinant protein (MorEst) was functionally expressed, purified and biochemically characterized, while its ability to degrade various synthetic polyesters (polyethylene terephthalate, polycaprolactone, polylactic acid, polyurethane) as well as model compounds was evaluated.