Internal Electric Field Boosts Enzyme-Catalyzed Polylactide Depolymerization

Abstract

Biodegradable plastics are regarded as alternatives to their petrochemical counterparts, offering reduced environmental impact and harmfulness. Emerging concerns indicate that even “biodegradable” plastics, such as polylactide (PLA), may persist in natural environments for a significant duration, posing environmental risks. Several promising PLA hydrolases and their variants have been recently characterized while leaving the catalytic mechanisms of proteases largely unexplored. Here, we elucidate the mechanism of PLA hydrolysis catalyzed by a serine protease, ProteinT^FLTIER, using extensive quantum mechanics/molecular mechanics molecular dynamics simulations. The whole enzymatic hydrolysis process involves three major stages: substrate binding, the catalytic process, and product release. Both substrate binding and product release hold relatively low free energy barriers (12.4–13.1 kcal·mol^–1), while the product formation step in the catalytic process is identified as the rate-determining step. It shows a free energy barrier of 15.6 kcal·mol^–1. Leveraging oriented external electric field studies, we demonstrate that a preorganized electric field originating from ProteinT^FLTIER facilitates the catalytic process. More importantly, we find significant differences in average electric field strength in the transition state and the reactant, which may further enhance catalytic efficiency. These insights are important for understanding the enzyme-catalyzed PLA depolymerization mechanism. They will contribute to the design of high-performance enzymes through the optimization of their internal electric fields.