Understanding the functional properties of bio-inorganic nanoflowers as biocatalysts by deciphering the metal-binding sites of enzymes

Immobilization of collagenase in inorganic hybrid nanoflowers with enhanced stability, proteolytic activity, and their anti-amyloid potential

Organic-inorganic hybrid nanomaterials are considered as promising immobilization matrix for enzymes owing to their markedly enhanced stability and reusability. Herein, collagenase was chosen as a model enzyme to synthesize collagenase hybrid nanoflowers (Col-hNFs). Maximum collagenase activity (155.58 μmol min-1 L-1) and encapsulation yield (90 %) were observed in presence of Zn(II) ions at 0.05 mg/mL collagenase, 120 mM zinc chloride and PBS (pH 7.5). Synthesized Col-Zn-hNFs were extensively characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR), circular dichroism (CD), fluorescence spectroscopy, dynamic light scattering (DLS) and zeta potential measurements. SEM images showed flower-like morphology with average size of 5.1 μm and zeta potential of -14.3 mV. Col-Zn-hNFs demonstrated superior relative activity across wide pH and temperature ranges, presence of organic solvents and surfactants as compared to its free form. Moreover, Col-Zn-hNFs exhibited excellent shelf life stability and favorable reusability. Col-Zn-hNFs showed the ability to suppress and eradicate fully developed insulin fibrils in vitro (IC50 = 2.8 and 6.2 μg/mL, respectively). This indicates a promising inhibitory potential of Col-Zn-hNFs against insulin amyloid fibrillation. The findings suggest that the utilization of Col-Zn-hNFs as a carrier matrix holds immense potential for immobilizing collagenase with improved catalytic properties and biomedical applications.

In silico approaches to investigate enzyme immobilization: a comprehensive systematic review

Enzymes are popular catalysts with many applications, especially in industry. Biocatalyst usage on a large scale is facing some limitations, such as low operational stability, low recyclability, and high enzyme cost. Enzyme immobilization is a beneficial strategy to solve these problems. Bioinformatics tools can often correctly predict immobilization outcomes, resulting in a cost-effective experimental phase with the least time consumed. This study provides an overview of in silico methods predicting immobilization processes via a comprehensive systematic review of published articles till 11 December 2022. It also mentions the strengths and weaknesses of the processes and explains the computational analyses in each method that are required for immobilization assessment. In this regard, Web of Science and Scopus databases were screened to gain relevant publications. After screening the gathered documents (n = 3873), 60 articles were selected for the review. The selected papers have applied in silico procedures including only molecular dynamics (MD) simulations (n = 20), parallel tempering Monte Carlo (PTMC) and MD simulations (n = 3), MD and docking (n = 1), density functional theory (DFT) and MD (n = 1), only docking (n = 11), metal ion binding site prediction (MIB) server and docking (n = 2), docking and DFT (n = 1), docking and analysis of enzyme surfaces (n = 1), only DFT (n = 1), only MIB server (n = 2), analysis of an enzyme structure and surface (n = 12), rational design of immobilized derivatives (RDID) software (n = 3), and dissipative particle dynamics (DPD; n = 2). In most included studies (n = 51), enzyme immobilization was investigated experimentally in addition to in silico evaluation.

Role of pretty nanoflowers as novel versatile analytical tools for sensing in biomedical and bioanalytical applications

In recent years, an encouraging breakthrough in the synthesis of immobilized enzymes in flower-shaped called "organic-inorganic hybrid nanoflowers (hNFs)" with greatly enhanced catalytic activity and stability were reported. Although, these hNFs were discovered by accident, the enzymes exhibited highly enhanced catalytic activities and stabilities in the hNFs compared with the free and conventionally immobilized enzymes. Herein, we rationally utilized the catalytic activity of the hNFs for analytical applications. In this comprehensive review, we covered the design and use of the hNFs as novel versatile sensors for electrochemical, colorimetric/optical and immunosensors-based detection strategies in analytical perspective.

Experimental and Computational Analysis of Synthesis Conditions of Hybrid Nanoflowers for Lipase Immobilization

This work presents a framework for evaluating hybrid nanoflowers using Burkholderia cepacia lipase. It was expanded on previous findings by testing lipase hybrid nanoflowers (hNF-lipase) formation over a wide range of pH values (5-9) and buffer concentrations (10-100 mM). The free enzyme activity was compared with that of hNF-lipase. The analysis, performed by molecular docking, described the effect of lipase interaction with copper ions. The morphological characterization of hNF-lipase was performed using scanning electron microscopy. Fourier Transform Infrared Spectroscopy performed the physical-chemical characterization. The results show that all hNF-lipase activity presented values higher than that of the free enzyme. Activity is higher at pH 7.4 and has the highest buffer concentration of 100 mM. Molecular docking analysis has been used to understand the effect of enzyme protonation on hNF-lipase formation and identify the main the main binding sites of the enzyme with copper ions. The hNF-lipase nanostructures show the shape of flowers in their micrographs from pH 6 to 8. The spectra of the nanoflowers present peaks typical of the amide regions I and II, current in lipase, and areas with P-O vibrations, confirming the presence of the phosphate group. Therefore, hNF-lipase is an efficient biocatalyst with increased catalytic activity, good nanostructure formation, and improved stability.

Hyperactivation of lipases by immobilization on superhydrophobic graphene quantum dots inorganic hybrid nanoflower

Various nanoflowers are synthesized for enzyme immobilization. In order to increase the activity of nanoflowers, in this study, 3D flower-like structured organic-inorganic hybrid nanoflowers (hNFs) with various lipases Rhizomucor miehei lipase (RML), Candida antarctica lipase B (CALB), Humicola insolens lipase (HIL), Thermomyces lanuginosus lipase (TLL), Eversa® Transform 2.0 (ET) a genetically modified enzyme derived of TLL and graphene quantum dots (GQDs) were prepared and characterized.Lipase hNFs [lipase-(Cu/Co)3(PO4)2] and lipase@GQDs hNFs [lipase@GQDs-(Cu/Co)3(PO4)2] were straightforwardly prepared through mixing with metal ion (Cu2+or Co2+) aqueous solutions with or without GQDs. The ET@GQDs-(Cu)3(PO4)2 hNFs demonstrated 687 % higher activity than ET-(Cu)3(PO4)2 hNFs and 650 % higher activity than the free ET. Similar results were also observed with other lipase hybrid nanoflowers. For example, TLL@GQDs-(Cu)3(PO4)2 hNFs exhibited a 557 % higher activity than TLL-(Cu)3(PO4)2 hNFs and a 463 % higher activity than free TLL. Additionally, TLL@GQDs-(Co)3(PO4)2 hNFs showed a 141 % higher activity than TLL-(Co)3(PO4)2 hNFs and a 304 % higher activity than free TLL. Upon examining pH and thermal stability, it was revealed that lipase@GQDs hNFs exhibited higher activity compared to free lipase and other hNFs without GQDs. The effect of metal ions, enzyme concentrations and amount of GQDs on the morphology and enzyme activity of the lipase-hNFs was examined.

In situ embedding of glucose oxidase in amorphous ZIF-7 with high catalytic activity and stability and mechanism investigation

Glucose oxidase (GOx) has a great application potential in the determination of glucose concentration. However, its sensitivity to the environment and poor recyclability limited its broader application. Herein, with the assistance of DA-PEG-DA, a novel immobilized GOx based on amorphous Zn-MOFs (DA-PEG-DA/GOx@aZIF-7/PDA) was developed to impart excellent properties to the enzyme. SEM, TEM, XRD, and BET analyses confirmed that GOx was embedded in amorphous ZIF-7 with ~5 wt% loading. Compared with free GOx, DA-PEG-DA/GOx@aZIF-7/PDA exhibited enhanced stability, excellent reusability, and promising potential for glucose detection. After 10 repetitions, the catalytic activity of DA-PEG-DA/GOx@aZIF-7/PDA can maintain 95.53 % ± 3.16 %. In understanding the in situ embedding of GOx in ZIF-7, the interaction of zinc ion and benzimidazole with GOx was studied by using molecular docking and multi-spectral methods. Results showed that zinc ions and benzimidazole had multiple binding sites on the enzyme, which induced the accelerated synthesis of ZIF-7 around the enzyme. During binding, the structure of the enzyme changes, but such changes hardly affect the activity of the enzyme. This study provides not only a preparation strategy of immobilized enzyme with high activity, high stability, and low enzyme leakage rate for glucose detection, but also a more comprehensive understanding of the formation of immobilized enzymes using the in situ embedding strategy.

Nanozymes and nanoflower: Physiochemical properties, mechanism and biomedical applications

Natural enzymes possess several drawbacks which limits their application in industries, wastewater remediation and biomedical field. Therefore, in recent years researchers have developed enzyme mimicking nanomaterials and enzymatic hybrid nanoflower which are alternatives of enzyme. Nanozymes and organic inorganic hybrid nanoflower have been developed which mimics natural enzymes functionalities such as diverse enzyme mimicking activities, enhanced catalytic activities, low cost, ease of preparation, stability and biocompatibility. Nanozymes include metal and metal oxide nanoparticles mimicking oxidases, peroxidases, superoxide dismutase and catalases while enzymatic and non-enzymatic biomolecules were used for preparing hybrid nanoflower. In this review nanozymes and hybrid nanoflower have been compared in terms of physiochemical properties, common synthetic routes, mechanism of action, modification, green synthesis and application in the field of disease diagnosis, imaging, environmental remediation and disease treatment. We also address the current challenges facing nanozyme and hybrid nanoflower research and the possible way to fulfil their potential in future.

Immobilization of Bacillus amyloliquefaciens protease "Neutrase" as hybrid enzyme inorganic nanoflower particles: A new biocatalyst for aldol-type and multicomponent reactions

Organic-inorganic hybrid nanoflowers (hNFs) with commercial protease "Neutrase" is proposed and characterized as efficient and green biocatalysts for promiscuous catalysis in aldol-type and multicomponent reactions. Neutrase hNFs [Neutrase-(Cu/Ca/Co/Mn)₃(PO₄)₂] are straightforwardly prepared through mixing metal ion (Cu²⁺, Ca²⁺, Co²⁺ or Mn²⁺) aqueous solutions with Neutrase in phosphate buffer (pH 7.4, 10 mM) resulting in precipitation (3 days). The hNFs were characterized by various techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX), element mapping, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In SEM images, the metal-Neutrase complexes revealed flower-like or granular structures after hybridization. The effect of metal ions and enzyme concentrations on the morphology and enzyme activity of the Neutrase-hNFs was examined. The synthesized Neutrase-Mn hNFs showed superior activity and stability compared to free Neutrase. Traditional organic CC coupling reactions such as aldol condensation, decarboxylative aldol, Knoevenagel, Hantzsch-type reactions and synthesis of 4H-pyran derivatives were used to test the generality and scope of Neutrase promiscuity, while optimizing conditions for the Neutrase-Mn hNF biocatalyst. Briefly, Neutrase-Mn₃(PO₄)₂ hNFs showed excellent enzyme activity, stability and reusability, qualifying as effective reusable catalysts for coupling reactions under mild conditions.

Mineralization of Lipase from Thermomyces lanuginosus Immobilized on Methacrylate Beads Bearing Octadecyl Groups to Improve Enzyme Features

Lipase from Thermomyces lanuginosus (TLL) has been immobilized on Purolite Lifetech® ECR8806F (viz. methacrylate macroporous resin containing octadecyl groups, designated as Purolite C18-TLL), and the enzyme performance has been compared to that of the enzyme immobilized on octyl-agarose, designated as agarose C8-TLL. The hydrolytic activity versus p-nitrophenol butyrate decreased significantly, and to a lower extent versus S-methyl mandelate (more than twofold), while versus triacetin and R-methyl mandelate, the enzyme activity was higher for the biocatalyst prepared using Purolite C18 (up to almost five-fold). Regarding the enzyme stability, Purolite C18-TLL was significantly more stable than the agarose C8-TLL. Next, the biocatalysts were mineralized using zinc, copper or cobalt phosphates. Mineralization increased the hydrolytic activity of Purolite C18-TLL versus triacetin and R-methyl mandelate, while this activity decreased very significantly versus the S-isomer, while the effects using agarose C8-TLL were more diverse (hydrolytic activity increase or decrease was dependent on the metal and substrate). The zinc salt treatment increased the stability of both biocatalysts, but with a lower impact for Purolite C18-TLL than for agarose-C8-TLL. On the contrary, the copper and cobalt salt treatments decreased enzyme stability, but more intensively using Purolite C18-TLL. The results show that even using enzymes immobilized following the same strategy, the differences in the enzyme conformation cause mineralization to have diverse effects on enzyme stability, hydrolytic activity, and specificity.

MIB2: metal ion-binding site prediction and modeling server

MOTIVATION

MIB2 (metal ion-binding) attempts to overcome the limitation of structure-based prediction approaches, with many proteins lacking a solved structure. MIB2 also offers more accurate prediction performance and more metal ion types.

RESULTS

MIB2 utilizes both the (PS)2 method and the AlphaFold Protein Structure Database to acquire predicted structures to perform metal ion docking and predict binding residues. MIB2 offers marked improvements over MIB by collecting more MIB residue templates and using the metal ion type-specific scoring function. It offers a total of 18 types of metal ions for binding site predictions.

AVAILABILITY AND IMPLEMENTATION

Freely available on the web at http://bioinfo.cmu.edu.tw/MIB2/.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Improvement in the Environmental Stability of Haloalkane Dehalogenase with Self-Assembly Directed Nano-Hybrid with Iron Phosphate

Haloalkane dehalogenase (DhaA) catalyzes the hydrolysis of halogenated compounds through the cleavage of carbon halogen bonds. However, the low activity, poor environmental stability, and difficult recycling of free DhaA greatly increases the economic cost of practical application. Inspired by the organic–inorganic hybrid system, an iron-based hybrid nanocomposite biocatalyst FeHN@DhaA is successfully constructed to enhance its environmental tolerability. A series of characterization methods demonstrate that the synthesized enzyme–metal iron complexes exhibit granular nanostructures with good crystallinity. Under optimized conditions, the activity recovery and the effective encapsulation yield of FeHN@DhaA are 138.54% and 87.21%, respectively. Moreover, it not only exhibits excellent immobilized enzymatic properties but also reveals better tolerance to extreme acid, and is alkali compared with the free DhaA. In addition, the immobilized enzyme FeHN@DhaA can be easily recovered and has a satisfactory reusability, retaining 57.8% of relative activity after five reaction cycles. The results of this study might present an alternative immobilized DhaA-based clean biotechnology for the decontamination of organochlorine pollutants.

Tuning Immobilized Commercial Lipase Preparations Features by Simple Treatment with Metallic Phosphate Salts

Four commercial immobilized lipases biocatalysts have been submitted to modifications with different metal (zinc, cobalt or copper) phosphates to check the effects of this modification on enzyme features. The lipase preparations were Lipozyme^®TL (TLL-IM) (lipase from Thermomyces lanuginose), Lipozyme^®435 (L435) (lipase B from Candida antarctica), Lipozyme^®RM (RML-IM), and LipuraSelect (LS-IM) (both from lipase from Rhizomucor miehei). The modifications greatly altered enzyme specificity, increasing the activity versus some substrates (e.g., TLL-IM modified with zinc phosphate in hydrolysis of triacetin) while decreasing the activity versus other substrates (the same preparation in activity versus R- or S- methyl mandelate). Enantiospecificity was also drastically altered after these modifications, e.g., LS-IM increased the activity versus the R isomer while decreasing the activity versus the S isomer when treated with copper phosphate. Regarding the enzyme stability, it was significantly improved using octyl-agarose-lipases. Using all these commercial biocatalysts, no significant positive effects were found; in fact, a decrease in enzyme stability was usually detected. The results point towards the possibility of a battery of biocatalysts, including many different metal phosphates and immobilization protocols, being a good opportunity to tune enzyme features, increasing the possibilities of having biocatalysts that may be suitable for a specific process.

Minimalist De Novo Design of an Artificial Enzyme

We employed a reductionist approach in designing the first heterochiral tripeptide that forms a robust heterogeneous short peptide catalyst similar to the "histidine brace" active site of lytic polysaccharide monooxygenases. The histidine brace is a conserved divalent copper ion-binding motif that comprises two histidine side chains and an amino group to create the T-shaped 3N geometry at the reaction center. The geometry parameters, including a large twist angle (73°) between the two imidazole rings of the model complex, are identical to those of native lytic polysaccharide monooxygenases (72.61°). The complex was synthesized and characterized as a structural and functional mimic of the histidine brace. UV-vis, vis-circular dichroism, Raman, and electron paramagnetic resonance spectroscopic analyses suggest a distorted square-pyramidal geometry with a 3N coordination at pH 7. Solution- and solid-state NMR results further confirm the 3N coordination in the copper center of the complex. The complex is pH-dependent and could catalyze the oxidation of benzyl alcohol in water to benzaldehyde with yields up to 82% in 3 h at pH 7 and above at 40 °C. The catalyst achieved 100% selectivity for benzaldehyde compared to conventional copper catalysis. The design of such a minimalist building block for functional soft materials with a pH switch can be a stepping stone in addressing needs for a cleaner and sustainable future catalyst.

Facile preparation of amorphous cobalt phosphate as inorganic carrier for direct separation and immobilization of his-tagged β-glucosidase from cell lysate

The present work was aimed to develop a facile method to fabricate solid support for the separation and immobilization of his-tagged enzymes directly from cell lysate without pre-purification of the enzymes.

Organic-inorganic epoxide hydrolase hybrid nanoflowers with enhanced catalytic activity: Hydrolysis of styrene oxide to 1-phenyl-1,2-ethanediol

Epoxide hydrolases are ubiquitous in nature and are utilized to catalyze the cofactor-independent hydrolysis of epoxides to their corresponding diols. These enzymes have tremendous potential and have been applied in the synthesis of bulk and fine chemical industry and utilized as chiral building blocks. Herein, we report a green, facile, and economical method for immobilization of epoxide hydrolase based on biomimetic mineralization. The organic-inorganic hybrid nanoflowers have received tremendous attention due to their higher catalytic activity and stability. The nanoflowers were synthesized, with the organic component being enzyme epoxide hydrolase and the inorganic component being Ca²⁺ ions. A unique hierarchical flower-like spherical structure with hundreds of spiked petals was observed. The synthesized nanoflowers were applied for styrene oxide hydrolysis, producing 1-phenyl-1,2-ethanediol. Further, the factors influencing the morphology, catalytic activity, and stability studies were performed to study the activity recovery of the synthesized organic-inorganic hybrid epoxide hydrolase nanoflowers. The findings will have interesting applications.

Self-assembly of soybean peroxidase nanohybrid for activity enhancement and dye decolorization: experimental and computational studies

The soybean peroxidase (SBP) mediated nanohybrid [SBP-Cu3(PO4)2·3H2O] synthesis was carried out in the present study. The scanning electron microscopy (SEM) analysis showed a characteristic flower-like hierarchical structure of the SBP-nanohybrid. The mechanism of SBP-nanohybrid formation was elucidated using computational approaches. The predicted Cu2+ binding sites followed by molecular docking studies showed the two lowest energy (-4.4 kcal/mol and -3.56 kcal/mol) Cu2+ binding sites. These two binding sites are located at the opposite position and might be involved in the formation of SBP-nanohybrid assemblies. Further, these sites are different than the catalytic active site pocket of SBP, and may facilitate more substrate catalysis. Obtained computational results were confirmed by in-vitro guaiacol oxidations studies using SBP-nanohybrid. The effect of various parameters on SBP-nanohybrid activity was studied. The pH 7.2 was found optimum for SBP-nanohybrid activity. The enzyme activity increased with an increase in temperature up to 50 °C temperature and then decreased with an increase in temperature. Around ∼138% enhanced activity was recorded using SBP-nanohybrid compared to crude SBP. Also, the SBP-nanohybrid showed around 95% decolorization of methylene blue (MB) in 1 h and the MB degradation was confirmed by high-pressure liquid chromatography analysis (HPLC).Communicated by Ramaswamy H. Sarma.

Understanding intricacies of bioinspired organic-inorganic hybrid nanoflowers: A quest to achieve enhanced biomolecules immobilization for biocatalytic, biosensing and bioremediation applications

The immobilization of biomolecules has been a subject of interest for scientists for a long time. The organic-inorganic hybrid nanoflowers are a new class of nanostructures that act as a host platform for the immobilization of such biomolecules. It provides better practical applicability to these functional biomolecules while also providing superior activity and reusability when catalysis is involved. These nanostructures have a versatile and straightforward synthesis process and also exhibit enzyme mimicking activity in many cases. However, this facile synthesis involves many intricacies that require in-depth analysis to fully attain its potential as an immobilization technique. A complete account of all the factors involving the synthesis process optimisation is essential to be studied to make it commercially viable. This paper explores all the different aspects of hybrid nanoflowers which sets them apart from the conventional immobilization techniques while also giving an overview of its wide range of applications in industries.

Immobilization of papain: A review

Papain is a cysteine protease from papaya, with many applications due to its broad specificity. This paper reviews for first time the immobilization of papain on different supports (organic, inorganic or hybrid supports) presenting some of the features of the utilized immobilization strategies (e.g., epoxide, glutaraldehyde, genipin, glyoxyl for covalent immobilization). Special focus is placed on the preparation of magnetic biocatalysts, which will permit the simple recovery of the biocatalyst even if the medium is a suspension. Problems specific to the immobilization of proteases (e.g., steric problems when hydrolyzing large proteins) are also defined. The benefits of a proper immobilization (enzyme stabilization, widening of the operation window) are discussed, together with some artifacts that may suggest an enzyme stabilization that may be unrelated to enzyme rigidification.

Preparation and application of quick hemostatic gauze based on biomimetic mineralized thrombin

Thrombin is a serine protease known as activated coagulation factor II and is primarily applied as an effective local hemostatic agent. However, its clinical application is hindered by drawbacks, such as high sensitivity to the surrounding environment, instability and poor storage stability, easy inactivation, and low bioavailability. The biological functions of biomacromolecules in harsh environments can be preserved through biomineralization. Despite the success of biomimetic mineralization, limited consideration has been given to the mineral-based methods and the effect of various metal ions on enzyme activity. To explore an efficient technique for biomimetic mineralized thrombin, six kinds of ion/thrombin hybrid microflowers and two kinds of thrombin/MOF were synthesized in this work. The results showed that Zn-HNFs-G exhibits good hemostatic effect and maintains high enzymatic activity when exposed to high-temperature conditions. Meanwhile, Fe-HNFs-G, Thrombin@ZIF-8-G and Thrombin@MAF-7-G possess negligible enzyme protection.

Development of a Hybrid Bioinorganic Nanobiocatalyst: Remarkable Impact of the Immobilization Conditions on Activity and Stability of β-Galactosidase

Hybrid bioinorganic biocatalysts have received much attention due to their simple synthesis, high efficiency, and structural features that favor enzyme activity and stability. The present work introduces a biomineralization strategy for the formation of hybrid nanocrystals from β-galactosidase. The effects of the immobilization conditions were studied, identifying the important effect of metal ions and pH on the immobilization yield and the recovered activity. For a deeper understanding of the biomineralization process, an in silico study was carried out to identify the ion binding sites at the different conditions. The selected β-galactosidase nanocrystals showed high specific activity (35,000 IU/g biocatalyst) and remarkable thermal stability with a half-life 11 times higher than the soluble enzyme. The nanobiocatalyst was successfully tested for the synthesis of galacto-oligosaccharides, achieving an outstanding performance, showing no signs of diffusional limitations. Thus, a new, simple, biocompatible and inexpensive nanobiocatalyst was produced with high enzyme recovery (82%), exhibiting high specific activity and high stability, with promising industrial applications.

Enzyme-Loaded Flower-Shaped Nanomaterials: A Versatile Platform with Biosensing, Biocatalytic, and Environmental Promise

As a result of their unique structural and multifunctional characteristics, organic-inorganic hybrid nanoflowers (hNFs), a newly developed class of flower-like, well-structured and well-oriented materials has gained significant attention. The structural attributes along with the surface-engineered functional entities of hNFs, e.g., their size, shape, surface orientation, structural integrity, stability under reactive environments, enzyme stabilizing capability, and organic-inorganic ratio, all significantly contribute to and determine their applications. Although hNFs are still in their infancy and in the early stage of robust development, the recent hike in biotechnology at large and nanotechnology in particular is making hNFs a versatile platform for constructing enzyme-loaded/immobilized structures for different applications. For instance, detection- and sensing-based applications, environmental- and sustainability-based applications, and biocatalytic and biotransformation applications are of supreme interest. Considering the above points, herein we reviewed current advances in multifunctional hNFs, with particular emphasis on (1) critical factors, (2) different metal/non-metal-based synthesizing processes (i.e., (i) copper-based hNFs, (ii) calcium-based hNFs, (iii) manganese-based hNFs, (iv) zinc-based hNFs, (v) cobalt-based hNFs, (vi) iron-based hNFs, (vii) multi-metal-based hNFs, and (viii) non-metal-based hNFs), and (3) their applications. Moreover, the interfacial mechanism involved in hNF development is also discussed considering the following three critical points: (1) the combination of metal ions and organic matter, (2) petal formation, and (3) the generation of hNFs. In summary, the literature given herein could be used to engineer hNFs for multipurpose applications in the biosensing, biocatalysis, and other environmental sectors.

Protein morphology drives the structure and catalytic activity of bio-inorganic hybrids

Bio-hybrid materials have received a lot of attention in view of their bio-mimicking nature. One such biomimetic material with catalytic activity are the protein derived floral nanohybrid. Copper phosphate coordinated flakes can be curated to distinct floral morphology using proteins. Structurally two different proteins with similar size and with no known enzymatic activity are used to evaluate the role of protein structure and morphology, on the structure-activity relationship of the developed hybrid nanoflowers. Globular protein BSA and bacterial microcompartment domain protein PduBB' are selected. PduBB' because of self-assembling nature forms extended sheets, whereas BSA lacks specific assembly. The developed hybrid NFs differ in their morphology and also in their mimicry as a biological catalyst. The present investigation highlights the importance of the quaternary structure of proteins in tailoring the structure and function of the h-NFs. The results in this manuscript will motivate and guide designing, engineering and selection of glue material for fabricating biomacromolecule derived biohybrid material to mimic natural enzymes of potential industrial application.

Organic-inorganic nanocrystal reductase to promote green asymmetric synthesis

An acetophenone reductase from Geotrichum candidum (GcAPRD) was immobilized by the organic–inorganic nanocrystal method. The GcAPRD nanocrystal presented improved stability and recyclability compared with those of the free GcAPRD. Moreover, the GcAPRD nanocrystal reduced broad kinds of ketones with excellent enantioselectivities to produce beneficial chiral alcohols such as (S)-1-(3′,4′-dichlorophenyl)ethanol with >99% yield and >99% ee. The robust and versatile properties of the GcAPRD nanocrystal demonstrated an approach to promote green asymmetric synthesis and sustainable chemistry.

Geotrichum candidum acetophenone reductase (GcAPRD) nanocrystal reduces broad kinds of ketones to their corresponding (S)-alcohols with excellent enantioselectivity.

Recyclable thermophilic hybrid protein-inorganic nanoflowers for the hydrolysis of milk lactose

Thermostable β-galactosidase (TmLac) has been immobilized as hybrid inorganic-protein nanoflowers using salts of Cu²⁺, Mn²⁺, Zn²⁺, Co²⁺ and Ca²⁺ as the inorganic component. The incorporation efficiency of enzyme into the nanoflowers was higher than 95% for a protein concentration of 0.05 mg/mL. The structure, activity and recyclability of the nanoflowers with different chemical composition were analyzed. Ca²⁺, Mn²⁺ and Co²⁺ nanoflowers showed a level of lactase activity equivalent to their same content of free enzyme. Cu²⁺nanoflowers showed only marginal enzyme activity in agreement with the inhibitory effect of this cation on the enzyme. TmLac nanoflowers provide an efficient methodology for enzyme immobilization and recyclability. TmLac-Ca²⁺ nanoflowers presented the best properties for lactose hydrolysis both in buffered and in milk, and could be reused in five consecutive cycles.

Organic-inorganic nanoflowers: from design strategy to biomedical applications

Organic-inorganic hybrid nanoflowers (NF) with sizes or features on a nanoscale are a class of flower-shaped nanomaterials self-assembled from metal ions and organic components. Here, to be more specific, the organic components mainly refer to biomolecules ranging from proteins, peptides, and amino acids to DNA/RNA. Beyond their pleasing aesthetics, their unique properties and integrated functions have attracted widespread interest and made them promising candidates in the application of biomedical areas. Great efforts have been made to design and synthesize versatile functional hybrid nanoflowers. In this review, we begin with the clarification of versatile recently reported hybrid nanoflowers according to the types of metal ions and biomolecules employed. To highlight the design of organic-inorganic hybrid nanoflowers, their synthetic methods and mechanisms, structural and biological characteristics are discussed. After that, the state-of-the-art applications of hybrid nanoflowers in biomedical fields including biosensing, biocatalysis, and cancer therapy are demonstrated. In the end, we discuss the prospects of organic-inorganic hybrid nanoflowers and highlight the challenges and opportunities for future research.

Engineering enzyme-coupled hybrid nanoflowers: The quest for optimum performance to meet biocatalytic challenges and opportunities

The current industrial revolution signifies the high-value of biocatalysis engineering. Over the past decade, multiple micro- and nanostructured materials have been attempted for immobilization of enzymes to improve their catalytic properties. Conventional immobilization strategies result in improved stability, while insolubilized enzymes generally lost their activity compared to free counterparts. Recently, a new generation organic-inorganic hybrid nanoflowers with unique properties have received great attention as a novel and incentive immobilization approach owing to their simple fabrication, high biocatalytic efficiency, and enzyme stabilizing capability. The hybrid nanoflowers biocatalytic system implicates metal ions and biomolecules (enzymes). In contrast to free or conventionally immobilized enzymes, single enzyme or multi enzyme-incorporated flowers-like hybrid nanoconstructs demonstrated elevated catalytic activities and stabilities over a very broader range of experimental conditions, i.e., pHs, temperatures and salt concentration. This review discusses the recent developments in the fabrication strategies to diversifying nanoflowers, types, characteristics, and applications of organic-inorganic hybrid nanoflowers as a host platform to engineer different kinds of enzymes with requisite functionalities for biocatalysis applications in different sectors of the modern world. Based on experimental and theoretical literature data, the review is wrapped up with concluding remarks and an outlook in terms of upcoming challenges and prospects for their scale-up applications.

Development of Effective Lipase-Hybrid Nanoflowers Enriched with Carbon and Magnetic Nanomaterials for Biocatalytic Transformations

In the present study, hybrid nanoflowers (HNFs) based on copper (II) or manganese (II) ions were prepared by a simple method and used as nanosupports for the development of effective nanobiocatalysts through the immobilization of lipase B from Pseudozyma antarctica. The hybrid nanobiocatalysts were characterized by various techniques including scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The effect of the addition of carbon-based nanomaterials, namely graphene oxide and carbon nanotubes, as well as magnetic nanoparticles such as maghemite, on the structure, catalytic activity, and operational stability of the hybrid nanobiocatalysts was also investigated. In all cases, the addition of nanomaterials during the preparation of HNFs increased the catalytic activity and the operational stability of the immobilized biocatalyst. Lipase-based magnetic nanoflowers were effectively applied for the synthesis of tyrosol esters in non-aqueous media, such as organic solvents, ionic liquids, and environmental friendly deep eutectic solvents. In such media, the immobilized lipase preserved almost 100% of its initial activity after eight successive catalytic cycles, indicating that these hybrid magnetic nanoflowers can be applied for the development of efficient nanobiocatalytic systems.

Preparation of laccase-loaded magnetic nanoflowers and their recycling for efficient degradation of bisphenol A

Bisphenol A (BPA) has been identified as one of the endocrine disrupting chemicals. However, the issue that BPA widely exists in various environments has puzzled people for decades. To develop highly efficient, easy separation, recyclable and reusable materials for BPA degradation in water, laccase-loaded magnetic nanoflowers (MNFs) were prepared by attaching amino-functionalized magnetic nanoparticles onto the laccase-inorganic hybrid nanoflowers. Characterization results showed that MNFs were spherical, porous and hierarchical structure with an average diameter of 15 μm to which magnetic nanoparticles was successfully attached through electrostatic force. MNFs exhibited excellent catalytic activity on BPA degradation under room temperature in the presence of ABTS. Under optimized conditions, MNFs reached 100% BPA degradation for only 5 min. In addition, it still retained over 92% of its initial activity after 60 days of storage at 4 °C, indicating that its thermal and storage stabilities have been improved. When the MNFs was recycled and reused 5 cycles, only 5% decrease in degradation efficiency of BPA was observed. These results suggest that MNFs possess great efficiency and reusability in the treatment of aqueous solution containing BPA and is a novel promising material.

Self-assembled 2,4-dichlorophenol hydroxylase-inorganic hybrid nanoflowers with enhanced activity and stability

2,4-Dichlorophenol hydroxylase (2,4-DCP hydroxylase) is a key enzyme in the degradation of 2,4-dichlorophenoxyacetic acid in the hydroxylation step in many bacteria. Our previous study demonstrated that a cold-adapted 2,4-DCP hydroxylase (tfdB-JLU) exhibits broad substrate specificity for chlorophenols, biphenyl derivatives and their homologues. However, the stability of this enzyme is not satisfactory in practical use. There have been no reports of immobilizing a cold-adapted enzyme to improve its activity and stability so far. This study for the first time reports a facile approach for the synthesis of hybrid nanoflowers (hNFs) formed from cold-adapted 2,4-dichlorophenol hydroxylase (tfdB-JLU) and Cu₃(PO₄)₂·3H₂O. The influence of experimental factors, such as the pH of the solution mixture and the enzyme and Cu²⁺ concentrations, on the activity of the prepared tfdB-JLU-hNFs is investigated. The morphologies of the tfdB-JLU-hNFs are further analyzed by SEM and TEM. Compared to the free enzyme, the tfdB-JLU-hNFs exhibit up to 162.46 ± 1.53% enhanced 2,4-dichlorophenol degradation activity when encapsulated at different enzyme concentrations. The tfdB-JLU-hNFs exhibit excellent durability with 58.34% residual activity after six successive cycles, and up to 90.58% residual activity after 20 days of storage. These results demonstrate that this multistage and hierarchical flower-like structure can effectively increase enzyme activity and stability with respect to those of the free enzyme. The satisfactory removal rate of 2,4-dichlorophenol catalyzed by tfdB-JLU-hNFs suggests that this immobilized enzyme exhibits great potential for application in bioremediation.

Highly stable and active hydroxylase-inorganic hybrid nanoflowers with great potential for application in bioremediation were obtained.

In situ hybridization of enzymes and their metal-organic framework analogues with enhanced activity and stability by biomimetic mineralisation

By incorporating Cytochrome c (peroxidase, Cyt c) into a skeleton of its corresponding synthetic MOF analogue (peroxidase mimic, CuBDC), approximately 12-fold catalytic efficiency (k_cat/K_M) enhancement is observed compared to free Cyt c. Meanwhile, the shield endowed by CuBDC prevents encapsulated enzymes from deactivation by trypsin digestion, thermal treatment and long-term storage in vitro. This concept of combining enzymes and their MOF mimics with enhanced enzymatic activity and stability may provide new insights into the design of highly active, stable enzyme-MOF composite catalysts and holds promise for applications in biocatalysis, biosensing and drug delivery systems.