Multienzyme System in Amorphous Metal–Organic Frameworks for Intracellular Lactate Detection

Abstract

Lactate is an important downstream product of glycolysis in living cells, and its level is highly related with diseases. On the basis of amorphous metal–organic frameworks (aMOFs), a multienzyme system consisting of lactate oxidase (LOx) and horseradish peroxidase (HRP) was established for intracellular lactate detection. By coencapsulation in aMOFs with proximity, LOx and HRP were delivered into cells, serving as artificially constructed organelles, exhibiting high activity and selectivity for the intracellular detection of the important metabolite lactate, which improved the signal to noise ratio by ∼650-fold. As demonstrated by both experimental and simulation results, the high efficiency was attributed to the short distance between the two types of enzymes coencapsulated in aMOFs. The concept of constructing multienzyme systems in this study shows promise for the detection of various intracellular metabolites.

Assessment of Enzyme Functionality at Metal–Organic Framework Interfaces Developed through Molecular Simulations

“…73 In addition to enzyme activity and stability, the proximity effect might be another key factor that affects the enzyme cascade overall activity under diffusion-restricted circumstances such as the ones found at the enzyme nanointerfaces, including the ones present in our study. 74 This interfacial phenomenon further helps to explain differences in immobilized CA activity on MIL-160 and ZIF-8 carriers reported by Liu et al, consistent with our findings herein. 25 Surface Analysis of Bound Enzymes.…”

“…Moreover, the analysis by Cao et al showed that palladium (Pd) nanoparticles (NPs) interfaced with Candida antarctic lipase B tunes the structure, dynamics, and catalysis of the enzyme with the enzyme–metal interface engineered within the polymer of interest to boost biometal cascade reactions via substrate channeling . In addition to enzyme activity and stability, the proximity effect might be another key factor that affects the enzyme cascade overall activity under diffusion-restricted circumstances such as the ones found at the enzyme nanointerfaces, including the ones present in our study . This interfacial phenomenon further helps to explain differences in immobilized CA activity on MIL-160 and ZIF-8 carriers reported by Liu et al, consistent with our findings herein …”

Expanding the “Library” of Metal–Organic Frameworks for Enzyme Biomineralization

“…Metal–organic frameworks (MOFs) are advanced platforms for enzyme immobilization and have provided advancement in biocatalysis, biomedicine, and fundamental biophysics research. − Thus far, major efforts in enzyme@MOF research have been focused on optimizing the metal, ligand, aperture, and/or pores of MOFs to enhance enzyme protection (against the reaction medium), reusability (as a result of the ease of separation), and substrate selectivity and/or diffusivity. − , While preformed, highly stable, and crystalline MOFs are mostly applied to host relatively small enzymes with small substrates, “one-pot” synthesis via co-crystallization of large enzymes and/or enzyme clusters with metals and ligands in the aqueous phase (also known as biomimetic mineralization) has been shown to be effective in removing the size limitation of enzymes. ,− Recently, researchers including our team have shown the possibility of using co-precipitation to remove the size limitation of the substrate, so that the entrapped enzymes are partially exposed to the reaction medium and partially buried under the MOF crystal surfaces, − as demonstrated on zeolitic imidazolate frameworks (ZIFs) and recent Ca-based metal–organic materials (MOMs, an analogue of MOFs but with a one- or two-dimensional structure); ,− the exposed enzyme regions were also revealed using our developed biophysical tools. , Importantly, our enzyme@Ca-MOM composites can be formed in the enzyme-friendly, aqueous phase under ambient conditions, minimizing the enzyme loss during co-precipitation . The Ca-MOMs are also stable under both weakly acidic and basic conditions, allowing for biocatalysis under the optimal pH of the immobilized enzyme.…”

Locking the Ultrasound-Induced Active Conformation of Metalloenzymes in Metal–Organic Frameworks

“…In the past few years, metal–organic frameworks (MOFs) have attracted wide interest for enzyme immobilization. − Composed of metal nodes and organic ligands, MOFs and their subclass zeolitic imidazolate frameworks (ZIFs) exhibit diverse chemical and structural features (such as shape, pore size, surface area, and structural flexibility). − These versatile features enable MOFs as an inert host as well as tailor the selectivity, stability, and/or activity of the enzymes while protecting them from unfavorable environments. − However, upon immobilization in MOFs, most enzymes experience a decreased activity due to the restricted enzyme conformation and substrate accessibility. Until now, increasing the pore size − and creating hollow cavities within MOFs have been the most popular strategies to improve the biocatalytic MOF activity. However, at the same time, these methods could reduce the immaculate MOF crystalline structure and the molecular sieving effect, thus leading to a low substrate selectivity as well as inferior resistance to the external harsh environment.…”