Protein Immobilization in Metal-Organic Frameworks by Covalent Binding

Metal-organic Frameworks (MOFs), possessing a well-defined system of pores, demonstrate extensive potential serving as a platform in biological catalysis. Successful immobilization of enzymes in a MOF system retains the enzymatic activity, renders the active site more accessible to the substrate, and promises recyclability for 10 reuse and solvent adaptability in a broad range of working conditions. This highlight describes enzyme immobilization on MOFs via covalent binding and its significance. Enzymatic catalysis, featuring high reactivity, selectivity, and specificity, has been extensively studied for chemical, pharmaceutical, and food industries. In commercial use, the 15 enzyme can be easily denatured by factors such as temperature, pH, and physical damage, resulting in loss of activity. Therefore, the successful industrial application of biological catalysis highly relies on the ability to stabilize these enzymes and proteins in an unnatural environment while retaining functionality and activity. [1] To solve the stability issue, studies have focused on incorporation of catalytically-active 20 centers of enzymes into synthetic materials or immobilization of the enzyme in organic or inorganic structures. Incorporation of active centers into synthetic materials would commonly result in the need for extensive enzyme engineering. Meanwhile, the latter strategy is extremely appealing to immobilize enzymes on gels, organic microparticles, nonporous and porous inorganic supports, as materials may be tailored prior to incorporation of enzymes. In particular, 25 immobilization of enzymes in the cavities of porous materials presents an unprecedented opportunity to achieve better efficiency by employing design principles inspired by nature in synthetic systems. [1, 2] The preliminary step to the use of biocatalysts in industrial application is to establish a solid support system. In this context, porous materials with high surface area, tunable but uniform pores, as well 30 as thermaland water-stability can serve as platforms for enzyme immobilization. In the past decade, metal-organic frameworks (MOFs) have emerged as ideal candidates for building heterogeneous catalytic systems owing to the vast diversity of structures, rich palettes of functionalities, large pore openings, tunable pore sizes, and permanent porosity. [2-4] Unlike traditional porous materials, such as zeolites, activated carbons, and mesoporous silica, MOFs 35 offer the opportunity of tuning the pore sizes and geometries, and chemical composition of the surfaces to instill desired properties by modifying metal/ligand combinations. This tunability of pore sizes allows for targeting of specific enzyme candidate. MOFs also prove attractive as they [*] Xuan Wang, Prof. H.-C. Zhou Department of Chemistry, Texas A&M University College Station, TX 77843 (USA) E-mail: [email protected] Homepage: http://www.chem.tamu.edu/rgroup/zhou/