pH Controlled Activation and Stabilization of Enzymes Using Responsive Polymer-Bioconjugates

Stimuli-responsive bioconjugates are developed to control enzymatic activity and stability using a pH-responsive polymer based on <i>N</i>,<i>N</i>-dimethyl aminopropylacrylamide. Prior work has shown that conjugating <i>N</i>-isopropylacrylamide (NIPAm) polymer to the<i>Candida antarctica</i> lipase B (CalB) enzyme has an inhibitory effect. Due to the similar hydrophobicity to the substrate of CalB, NIPAm polymer may block the enzyme's catalytic site, thereby inhibiting the enzyme's activity. This study shows that conjugating pDMAPA DP40-<i>b</i>-NIPAm DP10 to CalB has a pH-responsive effect on the catalytic property of CalB, with inverse stability responses. At low pH, where the polymer is extended, high activity is observed, while at low pH, the inhibitory block binds or occludes the active site and increases stability. A similar approach used a known inhibitor, <i>N</i>-acryloyl-d-glucosamine (AGA), for lysozyme. Conjugating pDMAPA DP40-<i>b</i>-AGA DP10 elicited a similar pH-controlled stability-activity response in lysozyme. Therefore, we propose that the polymer's pH-dependent interaction with protein can effectively regulate the protein between a highly active state and high stability behavior.