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  1. Enzyme encapsulation in metal-organic frameworks (MOFs)/covalent-organic frameworks (COFs) provides advancement in biocatalysis, yet the structural basis underlying the catalytic performance is challenging to probe. Here, we present an effective protocol to determine the orientation and dynamics of enzymes in MOFs/COFs using site-directed spin labeling and electron paramagnetic resonance spectroscopy. The protocol is demonstrated using lysozyme and can be generalized to other enzymes.
    Free, publicly-accessible full text available September 17, 2022
  2. Multiple-enzyme cooperation simultaneously is an effective approach to biomass conversion and biodegradation. The challenge, however, lies in the interference of the involved enzymes with each other, especially when a protease is needed, and thus, the difficulty in reusing the enzymes; while extracting/synthesizing new enzymes costs energy and negative impact on the environment. Here, we present a unique approach to immobilize multiple enzymes, including a protease, on a metal–organic material (MOM) via co-precipitation in order to enhance the reusability and sustainability. We prove our strategy on the degradation of starch-containing polysaccharides (require two enzymes to degrade) and food proteins (require amore »protease to digest) before the quantification of total dietary fiber. As compared to the widely adopted “official” method, which requires the sequential addition of three enzymes under different conditions (pH/temperature), the three enzymes can be simultaneously immobilized on the surface of our MOM crystals to allow for contact with the large substrates (starch), while MOMs offer sufficient protection to the enzymes so that the reusability and long-term storage are improved. Furthermore, the same biodegradation can be carried out without adjusting the reaction condition, further reducing the reaction time. Remarkably, the simultaneous presence of all enzymes enhances the reaction efficiency by a factor of ∼3 as compared to the official method. To our best knowledge, this is the first experimental demonstration of using aqueous-phase co-precipitation to immobilize multiple enzymes for large-substrate biocatalysis. The significantly enhanced efficiency can potentially impact the food industry by reducing the labor requirement and enhancing enzyme cost efficiency, leading to reduced food cost. The reduced energy cost of extracting enzymes and adjusting reaction conditions minimize the negative impact on the environment. The strategy to prevent protease damage in a multi-enzyme system can be adapted to other biocatalytic reactions involving proteases.« less
    Free, publicly-accessible full text available September 3, 2022
  3. Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy probes the otherwise inaccessible structural information in complex biological systems. We recently extended SDSL-EPR to reveal the relative orientation and backbone dynamics of enzymes upon encapsulation in mesoporous nanostructures, which set the structural basis underlying the observed biocatalytic activity. Our strategy had generated interest in the biocatalysis community, and thus in this resource article, we contribute an introduction to the principles and experimental procedure that generalize SDSL-EPR to heterogeneous biocatalysis. We will focus on enzymes in mesoporous materials with examples demonstrating the methods and cautions of potential pitfalls.more »The ultimate goal is to provide the biocatalysis community with a powerful resource to fill in a long-standing knowledge gap in heterogeneous biocatalysis and the structure-function relationship of enzymes at the interface of enzyme-mesoporous materials and utilize the structural insights to guide the rational design of porous platforms for enzyme immobilization.« less
  4. 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 originsmore »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.« less
  5. Metal–organic frameworks/materials (MOFs/MOMs) are advanced enzyme immobilization platforms that improve biocatalysis, materials science, and protein biophysics. A unique way to immobilize enzymes is co-crystallization/co-precipitation, which removes the limitation on enzyme/substrate size. Thus far, most enzyme@MOF composites rely on the use of non-sustainable chemicals and, in certain cases, heavy metals, which not only creates concerns regarding environmental conservation but also limits their applications in nutrition and biomedicine. Here, we show that a dimeric compound derived from lignin, 5,5′-dehydrodivanillate (DDVA), co-precipitates with enzymes and low-toxicity metals, Ca2+ and Zn2+, and forms stable enzyme@Ca/Zn–MOM composites. We demonstrated this strategy on four enzymes withmore »different isoelectric points (IEPs), molecular weights, and substrate sizes. Furthermore, we found that all enzymes displayed slightly different but reasonable catalytic efficiencies upon immobilization in the Ca–DDVA and Zn–DDVA MOMs, as well as reasonable reusability in both composites. We then probed the structural basis of such differences using a representative enzyme and found enhanced restriction of enzymes in Zn–DDVA than in Ca–DDVA, which might have caused the activity difference. To the best of our knowledge, this is the first aqueous-phase, one-pot synthesis of a lignin-derived “green” enzyme@MOF/MOM platform that can host enzymes without any limitations on enzyme IEP, molecular weight, and substrate size. The different morphologies and crystallinities of the composites formed by Ca–DDVA and Zn–DDVA MOMs broaden their applications depending on the problem of interest. Our approach of enzyme immobilization not only improves the sustainability/reusability of almost all enzymes but also reduces/eliminates the use of non-sustainable resources. This synthesis method has a negligible environmental impact while the products are non-toxic to living things and the environment. The biocompatibility also makes it possible to carry out enzyme delivery/release for nutritional or biomedical applications via our “green” biocomposites.« less