Discovery and engineering of cold-active lipases facilitating the biodegradation of poly(ε-caprolactone) and polyurethane from the functional mixed genomic library

Plastic pollution has become a serious environmental issue, leading to increased research efforts toward the development of biodegradable plastics. Poly(ε-caprolactone) (PCL) is a representative biodegradable polymer. PCL-based materials such as polyurethane (PU) still require long periods for degradation and consequently accumulate in the environment. The biopolymer degradation occurs through the hydrolysis of ester bonds, which can be significantly accelerated by enzymes such as esterases, cutinases, and lipases. Cold-active lipolytic enzymes isolated from extreme environments are promising candidates for various industrial and environmental applications. Accordingly, polar and alpine microbial strains were used as enzyme sources. Therefore, we aimed to elucidate the structural determinants of the catalytic efficiency of these enzymes against PCL and PU. Five cold-active lipases were identified in a fosmid library comprising bacterial genomic DNAs from 3062 strains, derived from the Polar and Alpine Microbial Collection (PAMC). These enzymes have homologous sequences between them and exhibited high lipolytic activity against plant oils. In particular, the enzymes PLI 131 and PLI 137 exhibited considerable activity against PCL and PU. A mutational analysis based on the protein structure model was performed using PLI 137 to improve the degrading activity against PCL and PU. These results suggest that specific loop regions near the lid domain of the protein are involved in the interactions with the PCL substrate. The alanine residue mutant in the loop also showed approximately two-fold greater activity against PCL. This study highlights the potential of cold-active lipases as eco-friendly biocatalysts for plastic biodegradation.