Metal–Organic Framework-Based Enzyme Biocomposites

Abstract

Due to their efficiency, selectivity, and environmental sustainability, there are significant opportunities for enzymes in chemical synthesis and biotechnology. However, as the three-dimensional active structure of enzymes is predominantly maintained by weaker non-covalent interactions, thermal, pH and chemical stressors can modify or eliminate activity. Metal-organic Frameworks (MOFs), which are extended porous network materials assembled by a bottom-up building block approach from metal-based nodes and organic linkers, can be used to afford protection to enzymes. The self-assembled structures of MOFs can be used to encase an enzyme in a process called encapsulation when the MOF is synthesized in the presence of the biomolecule. Alternatively, enzymes can be infiltrated into mesoporous MOF structures or surface bound via covalent or non-covalent processes. Integration of MOF materials and enzymes in this way affords protection and allows the enzyme to maintain activity in challenge conditions (e.g. denaturing agents, elevated temperature, non-native pH and organic solvents). In addition to forming simple enzyme/MOF biocomposites, other materials can be introduced to the composites to improve recovery or facilitate advanced applications in sensing and fuel cell technology. This review canvasses enzyme protection via encapsulation, pore infiltration and surface adsorption and summarizes strategies to form multi-component composites. Also, given that enzyme/MOF biocomposites straddle materials chemistry and enzymology, this review provides an assessment of the characterization methodologies used for MOF-immobilized enzymes and identifies some key parameters to facilitate development of the field. CONTENTSMOF-based enzyme biocomposite compositions and the concept of encapsulation 3.MOF-based enzyme biocomposites formed via encapsulation 3.1.Templating methods 3.2.One-pot embedding (non-templated) 3.3.Parameters influencing the chemistry of enzyme@MOF biocomposites 3.3.1. Additives 3.3.2.Enzyme suface chemistry 3.3.3.MOF precusors and structures 3.4.Alternative synthesis strategies 4.Infiltration (post insertion of enzymes in preformed MOFs) 4.1.Early results and the advantages of MOFs for infiltration 4.2.Tuning the framework structure in infiltrated enzyme@MOF biocomposites 4.3.Towards applications of infiltrated enzyme@MOFs 5.Surface bound enzymes 5.1. Immobilization via physical adsorption 5.2. Immobilization via coordinate bonds 5.3. Immobilization via covalent bonding 5.4. Enzymatic activity upon surface-immobilization 6. Multicomponent biocomposites 7. Characterization of MOF immobilized enzymes 7.1. Overview 7.2. Key immobilization parameters 7.3. One-pot enzyme MOF formation 7.4. Highlights of MOF-immobilized enzyme performance 7.4.1. Experimental determination of key immobilization parameters 7.4.1.1. Determination of protein concentrations 7.4.1.2. Activity determination 7.4.2. Advanced characterization of immobilized enzymes 7.4.2.1. Apparent enzyme kinetics 7.4.2.2. Structural analysis and localization o...

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

“…Enzymes can alternatively be encapsulated in the lattices of the MOF structure by mixing the enzyme with the metal and the ligand. In this case, encapsulation proceeds through a nucleation mechanism where the enzyme acts as a nucleus for MOF growth, leading to enzymes protected in pores with size close to the radius of gyration of the protein [147]. However, in the latter case, synthesis conditions must be mild enough to avoid protein denaturation.…”

“…We emphasized that MOFs are nowadays considered as very attractive materials. To ensure electron conduction within MOFs, multicomponent systems can be synthetized composed of MOFs, enzymes and conductive nanomaterials such as graphene nanosheets or CNTs [147]. A nice example is provided by Li et al who encapsulated a LAC in ZIF-8 in the presence of CNTs (LAC@ZIF-8) [247].…”

Assembly and Covalent Cross-Linking of an Amine-Functionalised Metal-Organic Cage

“…The applications of metal-organic frameworks (MOFs) have been rapidly expanding, with recent studies utilizing MOFs as crystallization matrices ( Bloch et al, 2015 ), sacrificial scaffolds for hierarchical porosity ( Dang et al, 2017 ; Haase et al, 2020 ), and protective agents in biomedicine ( Yang and Yang, 2020 ; Liang et al, 2021 ). The attractive properties of MOFs have largely been underpinned by important design principles surrounding their net topology ( Robson 2000 ), isoreticular chemistry ( Furukawa et al, 2013 ), and post-synthetic chemistry ( Mandal et al, 2021 ).…”

Stabilization of an enzyme cytochrome c in a metal-organic framework against denaturing organic solvents

“…MOFs are also attractive host materials for encapsulating enzymes as their porosity enables high enzyme loading, their crystallinity facilitates detailed bulk characterization, and their modularity allows for the design of frameworks tailored toward specific proteins ( Xia et al., 2020 ). The two primary strategies encapsulating enzymes in MOFs are (1) de novo encapsulation where MOFs are assembled around the enzymes ( He et al., 2016 ) and (2) post-synthetic encapsulation (PSE) during which enzymes diffuse into a premade MOF ( Drout et al., 2019 ; Majewski et al., 2017 ; Huang et al., 2020 ; Lian et al., 2017 ; Liang et al., 2021 ; Wang et al., 2020b ). With de novo encapsulation processes, the size and shape of the enzyme do not limit the portfolio of acceptable MOF supports.…”