Abstract
Co-precipitation of enzymes in metal-organic frameworks is a unique enzyme-immobilization strategy but is challenged by weak acid-base stability. To overcome this drawback, we discovered that Ca2+ can co-precipitate with carboxylate ligands and enzymes under ambient aqueous conditions and form enzyme@metal-organic material composites stable under a wide range of pHs (3.7–9.5). We proved this strategy on four enzymes with varied isoelectric points, molecular weights, and substrate sizes—lysozyme, lipase, glucose oxidase (GOx), and horseradish peroxidase (HRP)—as well as the cluster of HRP and GOx. Interestingly, the catalytic efficiency of the studied enzymes was found to depend on the ligand, probing the origins of which resulted in a correlation among enzyme backbone dynamics, ligand selection, and catalytic efficiency. Our approach resolved the long-lasting stability issue of aqueous-phase co-precipitation and can be generalized to biocatalysis with other enzymes to benefit both research and industry.
[Display omitted]
•Ca2+ and carboxylate ligands immobilize enzymes via co-precipitation in water•Enzyme@Ca-MOF biocomposites are stable under pH 3.7–9.5 and catalytically active•Biocatalysis is possible under a needed pH for optimal performance on our composites•SDSL and EPR are combined to elucidate enzymes' behavior in our composites
Enzymes are optimal biocatalysts for research and industry because of their excellent selectivity and biocompatibility, yet their high costs limit the practical and broad applications. Co-precipitation of enzymes with certain metals and ligands can immobilize an enzyme with arbitrary molecular weight and/or substrate size and improve reusability, yet the resultant biocomposites often suffer from poor stability under acidic or basic conditions, limiting biocatalytic reactions under the desired pHs. This work discovers a series of metal-organic materials that can be generalized to immobilize arbitrary enzymes to form biocomposites that are stable under a wide pH range that covers the optimal pHs of most commonly seen enzymes. The ease of preparation and the ambient reaction conditions are additional advantages. The platform can potentially change how industry utilizes enzymes for various purposes with desired catalytic efficiency and sustainability.
By co-precipitation of enzymes, Ca2+, and carboxylate ligands, we discovered the formation of biocomposites that are stable under a wide range of pHs (3.5–9.5). The catalytic activity was demonstrated on four enzymes with different sizes and isoelectric points. SDSL-EPR then revealed enhanced backbone dynamics of enzymes upon encapsulation in one of our biocomposites. The developed platform can be generalized to immobilize arbitrary enzymes and carry out catalytic reactions under the desired pH of the host enzyme.