A Combination of Two-Enzyme System and Enzyme Engineering Improved the Activity of a New PET Hydrolase Identified from Soil Bacterial Genome

We here report a novel PET hydrolase originating from a soil microbial genome sequence. This enzyme, bbPET0069, exhibits characteristics resembling a cutinase-like Type I PET-degrading enzyme but lacks disulfide bonds. Notably, bbPET0069 displayed remarkable synergy with Candida antarctica lipase B (CALB), demonstrating rapid and efficient PET degradation. To improve the PET degradation activity of bbPET0069, we employed a 3D structural modeling to identify mutation sites around its substrate binding domain combined with a protein language model for effective mutation prediction. Through three initial rounds of directed evolution, we achieved a significant enhancement in PET degradation with CALB, resulting in a 12.6-fold increase compared to wild-type bbPET0069 without CALB. We confirmed its PET degradation activity in PET nanoparticles and films, and our proposed approach enabled efficient PET degradation to terephthalic acid monomers up to 95.5%. Our approach, which integrates a two-enzyme system with protein engineering, demonstrates the potential for enhancing the activity of emerging PET-degradation enzymes, which may possess unique attributes.