Polyesterase activity is widespread in the family IV carboxylesterases from bacteria

Enzyme-based depolymerization of plastics, including polyesters, has emerged as a promising approach for plastic waste recycling and reducing environmental plastic pollution. Currently, most of the known polyester-degrading enzymes are represented by a few natural and engineered PETases from the carboxylesterase family V. To identify novel groups of polyesterases, we selected 25 proteins from the carboxylesterase family IV, which share 22 % to 80 % sequence identity to the metagenomic thermophilic polyesterase IS12. All purified proteins were found to be active against chromogenic para-nitrophenyl esters with a preference for short acyl chains. Screening for polyesterase activity using emulsified polyesters demonstrated the presence of hydrolytic activity against bis(benzoyloxyethyl) terephthalate (3PET), polycaprolactone (PCL), and polylactic acid (PLA) in all tested proteins. Biochemical characterization of four selected polyesterases revealed high thermostability in CBA10055, whereas the mesophilic GEN0105 exhibited higher polyesterase activity. Two ancestral variants of GEN0105 showed higher thermostability and activity against PCL and PLA, but reduced activity with amorphous PET. Furthermore, six established PETases were found to be highly active against PCL and PLA. Thus, our results indicate that polyesterase activity is widespread in the family IV carboxylesterases, and that most polyesterases are promiscuous being able to degrade different polyesters.