Embedding Dual-Responsive Polymer@Enzyme in Zeolitic Imidazolate Frameworks with a Hollow Space for Improving Its...

Herein, a stimuli-responsive polymer-support and sacrificial template strategy was introduced to modulate enzyme conformation freedom and generate nanoconfinement in porous zeolitic imidazolate framework-8 (ZIF-8), addressing challenges in realizing improved catalytic performance, tolerance, and stability. A thermo- and pH-responsive poly(styrene-maleic anhydride-2-hydroxyethyl methacrylate) was synthesized via a reversible addition-fragmentation chain transfer polymerization protocol. Through a chemical bonding strategy, alanine aminotransferase was immobilized on the smart polymer. Using pluronic F-127 as a sacrificial template, smart polymer@alanine aminotransferase was embedded in pluronic F-127 to form smart polymer@alanine aminotransferase@pluronic F-127. Following in situ ZIF-8 shell growth and removal of pluronic F-127 by water, smart polymer@alanine aminotransferase@HSZIF-8 composites with a hollow space were fabricated. Strikingly, the smart polymer played the "tunable switch" role in controlling the enzymatic reaction, changing its morphology by varying external temperatures and pH values, further yielding nanoconfinement. Remarkably, the proposed composites exhibited higher catalytic activity (K_cat/K_m), 13.92-fold enhancement in comparison with free alanine aminotransferase under 45.0 °C at pH 4.5, meanwhile, with remaining outstanding catalytic performance and great stability toward harsh pH, heating, and exposure to organic solvents. Additionally, the composites and a capillary electrophoresis method were successfully applied to evaluate the alanine aminotransferase activity in mice organs with l-alanine as the substrate. This study not only provides insights into the key role of a smart polymer, nanoconfinement, and a hollow space in metal organic frameworks but also establishes a way for developing metal organic framework-based carriers capable of improving enzyme activity and stability and shows great potential in bioapplication in real bioliving systems.