Hyper-Expandable Cross-Linked Protein Crystals as Scaffolds for Catalytic Reactions

Abstract

Scaffolding catalytic reactions within porous materials is a powerful strategy to enhance the reaction rates of multicatalytic systems. However, it remains challenging to develop materials with high porosity, high diversity of functional groups within the pores, and guest-adaptive tunability. Furthermore, it is challenging to capture large catalysts such as enzymes within porous materials. Protein-based materials are promising candidates to overcome these limitations, owing to their large pore sizes and potential for stimuli-responsive adaptability. In this work, hydrogel beads were generated from cross-linked lysozyme crystals. These swellable lysozyme cross-linked crystals (SLCCs) expand more than 10 mL per gram of crystal following a simple treatment in ethanol, followed by the addition of water. SLCCs are sensitive to the solution environment and change their extent of swelling from adjusting the concentration and identity of the ions in the solution, or by changing the flexibility of the protein backbone, such as adding dithiothreitol to reduce the protein disulfide bonds. SLCCs can adsorb a wide range of catalysts ranging from transition metal complexes to large biomacromolecules, such as the 160 kDa enzyme glucose oxidase (GOx). Transition metal catalysts and enzymes captured within SLCCs maintained their catalytic activity and exhibited minimal leaching. We performed a cascade reaction by adsorbing GOx and the transition metal catalyst Fe-TAML into SLCCs, resulting in enhanced activity compared to a free-floating reaction. SLCCs offer a promising combination of attributes as scaffolds for multicatalytic reactions, including gram-scale batch preparation, tunable expansion to greater than 20-fold in volume, guest-responsive adaptable behavior, and facile capture of a wide array of small molecule and enzyme-catalysts.