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Discovery and mechanism-guided engineering of BHET hydrolases for improved PET recycling and upcycling

Nature Communications 2023 86 citations

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Researchers identified and engineered two enzymes — called BHETases — that efficiently break down PET plastic (the kind used in bottles and packaging) into its chemical building blocks, achieving up to seven times better output than leading existing enzymes. By coupling these improved enzymes in a two-step system, the team demonstrated a path toward true closed-loop PET recycling.

Polymers

Although considerable research achievements have been made to address the plastic crisis using enzymes, their applications are limited due to incomplete degradation and low efficiency. Herein, we report the identification and subsequent engineering of BHETases, which have the potential to improve the efficiency of PET recycling and upcycling. Two BHETases (ChryBHETase and BsEst) are identified from the environment via enzyme mining. Subsequently, mechanism-guided barrier engineering is employed to yield two robust and thermostable ΔBHETases with up to 3.5-fold enhanced kcat/KM than wild-type, followed by atomic resolution understanding. Coupling ΔBHETase into a two-enzyme system overcomes the challenge of heterogeneous product formation and results in up to 7.0-fold improved TPA production than seven state-of-the-art PET hydrolases, under the conditions used here. Finally, we employ a ΔBHETase-joined tandem chemical-enzymatic approach to valorize 21 commercial post-consumed plastics into virgin PET and an example chemical (p-phthaloyl chloride) for achieving the closed-loop PET recycling and open-loop PET upcycling.

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