Cutinase Adsorption to Polyester Surfaces Modulates Dissolved Oligomer Speciation during Enzymatic Depolymerization

Surface-active enzymes, such as cutinases, initiate depolymerization of polyester plastics by adsorbing to the polymer surface. The influence of enzyme adsorption on the composition of dissolved degradation products remains underexplored. This study investigated how adsorption of a cutinase from Humicola insolens (HiC) to polyester surfaces modulated dissolved oligomer speciation during depolymerization of poly(butylene succinate) (PBS) and poly(butylene sebacate-co-terephthalate) (PBSeT). Inverse and conventional Michaelis-Menten kinetics were used to determine attack site densities (Γattack) and catalytic turnover (kcat). HiC exhibited comparable Γattack for PBS and PBSeT (0.31 ± 0.06 and 0.51 ± 0.12 μmolenzyme gplastic-1, respectively), while the kcat was 2 orders of magnitude higher for PBS (40.8 ± 8.4 s-1 vs 0.13 ± 0.02 s-1). Liquid chromatography coupled to mass spectrometry revealed accumulation of larger oligomers when the enzyme-to-plastic ratios were below the Γattack, indicating that relative free protein levels influence the composition of dissolved products during plastic depolymerization.