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Discovery and rational engineering of PET hydrolase with both mesophilic and thermophilic PET hydrolase properties
Summary
Researchers discovered a new enzyme from a soil bacterium that can break down PET plastic — the material in most plastic bottles — at both room temperature and elevated heat, then engineered an improved version that degrades PET powder almost completely within half a day at 55°C. This dual-temperature capability makes it more practical than existing enzymes for industrial-scale plastic recycling and could help address the global PET waste problem.
Excessive polyethylene terephthalate (PET) waste causes a variety of problems. Extensive research focused on the development of superior PET hydrolases for PET biorecycling has been conducted. However, template enzymes employed in enzyme engineering mainly focused on IsPETase and leaf-branch compost cutinase, which exhibit mesophilic and thermophilic hydrolytic properties, respectively. Herein, we report a PET hydrolase from Cryptosporangium aurantiacum (CaPETase) that exhibits high thermostability and remarkable PET degradation activity at ambient temperatures. We uncover the crystal structure of CaPETase, which displays a distinct backbone conformation at the active site and residues forming the substrate binding cleft, compared with other PET hydrolases. We further develop a CaPETaseM9 variant that exhibits robust thermostability with a Tm of 83.2 °C and 41.7-fold enhanced PET hydrolytic activity at 60 °C compared with CaPETaseWT. CaPETaseM9 almost completely decompose both transparent and colored post-consumer PET powder at 55 °C within half a day in a pH-stat bioreactor.