Solid-state enzyme stabilization by diffusion and chemical matching

Stabilizing enzymes in solid-state biodegradable plastics matrices is a central challenge for enabling enzymatic degradation under harsh processing and composting conditions. Here, we investigate Proteinase K (ProK) embedded in random heteropolymer-poly(L-lactic acid) (RHP-PLLA) composites as a model system for enzyme-assisted PLLA degradation. Molecular dynamics simulations show that PLLA can penetrate the RHP shell due to favorable RHP-PLLA mixing, allowing substrate enzymatic access. Protein stability depends on both matrix chemistry and heating time during polymer extrusion. High-Tg homopolymers and ionomeric RHPs provide superior stabilization, while low-Tg systems fail to protect ProK. Analysis of translational and rotational diffusion coefficients shows that enzyme stability is enhanced when enzyme diffusion is reduced and matched with matrix diffusion. In addition, chemical specificity contributes. RHPs enriched in hydrophobic monomers form hydrophobic and PEG-mediated contacts with ProK that are dynamic at the individual level but with the overall number remaining stable. This behavior is consistent with experimentally observed degradation rates. These findings establish diffusion matching and chemical matching as dual principles for designing robust polymer-enzyme hybrids for sustainable plastic degradation.