Noncovalent PEGylation-based enzyme switch in physiological saline conditions using quaternized polyamines

Recently, on/off switching of enzyme activity by noncovalent complexation with polyelectrolytes has been developed for biotechnological application. However, noncovalent complexation based on electrostatic interaction is unfavorable at high ionic strengths where Debye screening minimizes the attractive forces between the protein and the polyelectrolyte. In this study, we use quaternization and introduce ethyl, 1-hydroxyethyl, and benzyl groups into the amino groups of a cationic polyelectrolyte to extend the applicability of on/off switching in physiological conditions. The quaternization of poly(N,N-dimethylaminoethyl methacrylate)-block-poly(ethylene glycol) slightly improved the inhibition efficiencies of anionic α-amylase in both low and high ionic conditions. The introduced benzyl groups further enhanced the affinity with α-amylase as compared with other groups. Nevertheless, a tertiary structure of α-amylase was almost retained after complexation. The data indicate that both the charge density and the hydrophobic groups play indispensable roles in the formation of the stable enzyme–polyelectrolyte complex under physiological salt concentrations.