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Phenolic contamination is one of the crucial concerns for the safety of drinking water. Enzymatic degradation is a green and efficient manner for phenolic compounds removal from water. However, enzymatic degradation of phenolic pollutants in water is limited as a result of the low activity, stability and reusability of the enzyme. Herein, we propose a novel strategy to degrade phenolic pollutants in water by using an enzyme‐metal hybrid catalyst constructed by in situ formation of ultrafine Cu nanoparticles on the cross‐linked Laccase aggregates. The designed Cu/Lac CLEAs showed excellent performance on phenolic pollutants removal due to the cooperative catalysis between Lac CLEA and Cu NPs and the enrichment of phenolic pollutants in hybrid catalyst. The degradation efficiency of 2,4,6‐trichlorophenol catalyzed by Cu/Lac CLEAs was improved by 33 % compared to the Lac CLEAs, while Cu NPs barely catalyzed the degradation process of phenolic pollutants. The Cu/Lac CLEAs hybrid catalyst exhibit high catalytic activity at room temperature in a wide pH range of 5–8, making the degradation of phenolic pollutants more practically operational. In other words, this study develops a novel hybrid catalyst for the efficient removal of pollutants from water. [ABSTRACT FROM AUTHOR]

Enzymatic degradation of biomass is preferred over chemical methods for environmental protection. However, in most cases, a chemical pretreatment is still required to help improve enzyme accessibility of the biomass. Therefore, it is necessary to develop highly efficient enzymes for those reasons and to save costs accordingly. Costs can be further reduced if the enzymes are recycled. XynR8(N58D) is an engineered and highly active xylanase originating from the rumen fungus Neocallimastix patriciarum. In this study, XynR8(N58D) was extracellularly over-expressed by Pichia pastoris. The resulting crude enzyme solution, with a purity of XynR8(N58D) of over 80%, was used to prepare the cross-linked enzyme aggregates (CLEA) of XynR8(N58D). Specific activity of the crude enzyme solution was 11,599.39 IU/mg, and that of CLEA was 6129.42 IU/mg. The immobilization yield and the immobilization efficiency were 62.68 ± 16.20% and 84.31 ± 3.11%, respectively. The thermostability, stress tolerance, and shelf life of CLEA were significantly better than those of the free enzyme. The free enzyme and CLEA both effectively decomposed insoluble xylan and autoclaved corncob powders. Therefore, XynR8(N58D) made into CLEA not only maintained high activity, but also improved its stability and permitted its reuse or recyclability. Both forms of the enzyme can effectively degrade lignocellulosic biomass without relying on chemical pretreatment to reduce recalcitrance of the biomass structure. The application of XynR8(N58D) and its CLEA to biomass degradation can help establish an eco-friendly and more cost-effective process. [ABSTRACT FROM AUTHOR]

The presence of antibiotics in water systems and drinking water has detrimental effects on various organisms and poses health risks to both animals and humans. This study describes a sustainable approach using laccases to remove ciprofloxacin from water solutions. Laccases produced by monoculture of Trametes villosa and in co-culture with Pycnoporus sanguineus were immobilized using the method of cross-linked enzyme aggregates (CLEAs). The immobilization process was statistically optimized, and the biocatalysts were characterized and applied for biodegradation of ciprofloxacin at different concentrations. Laccase production was enhanced in co-culture conditions, yielding isoforms of molecular masses ranging from 55 to 45 kDa. Optimum conditions for immobilizing laccases by CLEAs were achieved with ammonium sulfate as a precipitant and glutaraldehyde as a cross-linker. Immobilization improved the thermal stability of the enzymes at 40 °C and 55 °C, and both forms of laccase CLEAs retained approximately 38% of their initial activity after five reuse cycles. Free and immobilized laccases demonstrated comparable efficiency in removing ciprofloxacin from aqueous solutions (at 2.5 mg L−1) with a 53–62% removal rate in the presence of 4-hydroxybenzoic acid as a natural redox mediator. The degradation of ciprofloxacin by laccases also reduced its antimicrobial activity against Escherichia coli. [Display omitted] • Co-culture of Trametes villosa with Pycnoporus sanguineus enhances laccase production. • Laccases immobilized as CLEAS exhibited improved thermal stability and reusability. • Free and immobilized laccases effectively catalyzed the degradation of ciprofloxacin • Enzymatic biodegradation of ciprofloxacin reduced its action against Escherichia coli. [ABSTRACT FROM AUTHOR]

Enzymes are commonly used as biocatalysts for various biological and chemical processes. However, some major drawbacks of free enzymes (e.g. poor reusability and instability) significantly restrict their industrial practices. How to overcome these weaknesses remain considerable challenges. Enzyme immobilization is one of the most effective ways to improve the reusability and stability of enzymes. Cross-linked enzyme aggregates (CLEAs) has been known as a novel and versatile carrier-free immobilization method. CLEAs is attractive due to its simplicity and robustness, without purification. It generally shows: high catalytic specificity and selectivity, good operational and storage stabilities, and good reusability. Moreover, co-immobilization of different kinds of enzymes can be acquired. These CLEAs advantages provide opportunities for further industrial applications. Herein, the preparation parameters of CLEAs were first summarized. Next, characterization of structural and catalytic properties, stability and reusability are also proposed. Finally, some important applications of this technique in: environmental protection, industrial chemistry, food industry, and pharmaceutical synthesis and delivery are introduced. Potential challenges and future research directions, such as improving cross-linking efficiency and internal mass transfer efficiency, are also presented. This implies that CLEAs provide an efficient and feasible technique to improve the properties of enzymes for use in the industry. [ABSTRACT FROM AUTHOR]

The traditional method for natural products discovering could be time-consuming and labor-intensive, thus ligand fishing has attracted a lot of attention as a fast-screening method. Nevertheless, ligand fishing often relied on immobilized enzyme with solid carriers, which can be expensive and complicated to prepare. In this study, a carrier-free enzyme immobilization technology, cross-linked enzyme aggregates (CLEAs), was introduced by preparing carbonic anhydrase cross-linked enzyme aggregates (CA-CLEAs), aiming to develop a method for ligand fishing that is simpler, faster and more cost-effective. CA-CLEAs were synthesized with optimal conditions, and were proven to have the ability to capture CA inhibitors and recycle. The crude extract of Salvia miltiorrhiza (SM) was determined to have inhibitory activity against CA, and two major components of SM, i.e., phenolic acids and diterpenoids, were prepared and incubated with CA-CLEAs, respectively. Seven potential inhibitors were fished out and identified using liquid chromatography-mass spectrometry (LC-MS), and all of them were verified to have inhibitory activity, with two novel inhibitors, salvianolic acid C and tanshinone IIA, being discovered. Molecular docking simulations revealed the different inhibitory mechanisms of phenolic acids and diterpenoids. Furthermore, combination effect analysis was carried out, and the synergistic effects were discovered between two components, as well as between their representative compounds, i.e., salvianolic acid B and tanshinone IIA. In this study, a ligand fishing method based on carrier-free immobilized enzyme was established and applied to discover CA inhibitors. A variety of inhibitors with different inhibitory mechanisms were identified successfully, which could accelerate the development of CA inhibitors, demonstrating the efficiency and potential of the method in new bioactive compounds discovery. [Display omitted] • A novel, efficient, reusable and economical ligand fishing method based on carrier-free immobilized enzyme was established. • The established method was applied to discover carbonic anhydrase (CA) inhibitors from Salvia miltiorrhiza (SM). • A novel type of CA inhibitors was discovered from SM. • The synergy between phenolic acids and diterpenoids in inhibiting CA was first revealed. [ABSTRACT FROM AUTHOR]

Bio-imprinted magnetic cross-linked enzyme aggregates (i-m-CLEAs) of polyphenol oxidase (PPO) obtained from potato peels were prepared using amino-functionalized magnetic nanoparticles. Bio-imprinting is being used to improve the catalytic efficiency and conformational stability of enzymes. For bio-imprinting, PPO was incubated with different imprint/template molecules (catechol, 4-methyl catechol and l-3,4-dihydroxy phenylalanine) before cross-linking with glutaraldehyde. CLEAs imprinted with 4-methyl catechol showed maximum activity as compared with non-bio-imprinted magnetic CLEAs (m-CLEAs). They were further characterized by scanning electron microscopy and confocal microscopy. In bio-imprinted m-CLEAs, half-life (t 1/2) of PPO significantly improved (364.74 min) as compared to free PPO (43.58 min) and non-bio-imprinted m-CLEAs (266.54 min). Bio-imprinted m-CLEAs showed excellent thermal and storage stability as well as reusability. The CLEAs preparation were used for the synthesis of l-3,4-dihydroxyphenylalanine (L-dopa, a therapeutic drug to treat neurodegenerative disorder) and a remarkable increase in L-dopa yield (23.5-fold) was obtained as compared to free enzyme. A cost effective and reusable method has been described for the production of L-dopa. [Display omitted] • Bio-imprinted magnetic cross-linked enzyme aggregates of PPO formation. • Improved catalytic activity, stability and reusability of bio-imprinted magnetic CLEAs • Economical method to produce L-dopa, a neurodegenerative therapeutic drug • Catalytic activity improved to 23.5-fold compared to free enzyme. [ABSTRACT FROM AUTHOR]

Organometallic catalyst is extensively applied for the non-enzymatic regeneration of nicotinamide adenine dinucleotide (phosphate) cofactors, but suffering from the mutual inactivation with the enzymes in one pot. The spatially separated immobilization of organometallic catalyst and enzymes on suitable carriers not only can reduce their mutual inhabitation but also can enhance their reusability. Here in this work, we present a hierarchical porous COFs (HP-TpBpy) that incorporated with [(Cp*RhCl 2 ] 2 to generate the metalized COF, Rh-HP-TpBpy. The obtained Rh-HP-TpBpy exhibited superior performance in nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH) regeneration using formate as the hydride donor, significantly outperforming the natural formate dehydrogenases in cofactor preference toward NADP+. Subsequently, the Lactobacillus fermentum short-chain dehydrogenase/reductase 1 (Lf SDR1) was then cross-linked into enzyme aggregates (CLEA) and immobilized on hierarchical Rh-HP-TpBpy, achieving the integrated chemoenzymatic catalyst, Lf SDR1@Rh-HP-TpBpy, which can catalyze the chemoenzymatic reduction of halogenated aryl ketones and give the corresponding optically active halohydrins with high conversion and enantiomeric excess (ee) value up to 99 %. The Lf SDR1@Rh-HP-TpBpy also exhibits largely enhanced stability compared with the free Lf SDR1 and the CLEAs -Lf SDR1, enabling its excellent reusability. • Hierarchical porous covalent organic framework (HP-COF) carrier is prepared by templet assistant method • The Rh complex and the CLEA- Lf SDR1 are immobilized on HP-COF for integration and spatial separation. • The co-immobilized Rh complex and CLEA- Lf SDR1 both exhibits largely enhanced stability and reusability. • A series of optically active halohydrins can be synthesized by HP-COF based chemoenzymatic nanoreactors. [ABSTRACT FROM AUTHOR]

Laccase from Trametes villosa was immobilized by CLEAs (cross-linked enzyme aggregates), biochemically characterized and applied for the degradation of the antibiotics rifampicin (RIF) and isoniazid (INH). The extracellular laccase purified by Sephadex G-100 chromatography presented a specific activity of 530.07 U/mg with a purification factor of 6.3-fold. SDS–PAGE followed by zymogram provided a single band, indicating that laccase from T. villosa was a monomeric protein with molecular mass of about 45 kDa. The optimum pH and temperature values for the laccase CLEAs (Lac-CLEAs) were 4.0 and 60 °C, respectively, and they remained more active over a broader range of pH and temperature during 60 min of incubation as compared to the partially purified free form. Lac-CLEAs presented less affinity for ABTS than their corresponding free enzyme, and the values for Km and Vmax were 3.521 mM and 137.0 mM min, respectively. Free laccases and Lac-CLEAs were used for simultaneous biodegradation of 5 mg/L RIF and INH in aqueous solutions. Results obtained by high-performance liquid chromatography (HPLC) revealed that 95% and 94% of RIF were biodegraded by free and immobilized laccase, respectively. Lac-CLEAs degraded more than twofold (71%) the amount of INH degraded by the free enzyme (32%). A microbial susceptibility assay demonstrated a stronger inhibition of Staphylococcus aureus by laccase-treated samples, with lower MIC values in comparison to control samples. Article Highlights: Trametes villosa produced 12 U/mL of laccase in semi solid cultures. Apparent molecular mass of the laccase from T. villosa was 45 kDa. Lac-CLEAs were more stable than the free enzyme at pH 6.0 and T ≥ 60 °C. Both free laccase and Lac-CLEAs biodegraded rifampicin and isoniazid. Isoniazid was more efficiently degraded by Lac-CLEAs. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is a strong oxidant chemical used asa bleach in the textile industry and it is important to remove it from water before being released to the environment. The oxidizing substrate of peroxidase (HRP) enzyme is hydrogen peroxide. In this study, cross-linked aggregates (CLEA) of HRP enzyme were used to remove hydrogen peroxide and glutaraldehyde (GA) was used as a crosslinking agent.When the kinetic constants of the free peroxidase enzyme were calculated, saturation constant was 0,06965 mmol H2O2/L and maximum specific rate constant was found as 0.0232mmol H2O2/L.sec. Average saturation constant, Kmof HRP-CLEA was found as 0,00625 mmol H2O2/L, and average maximum specific rate constant value, Vm, was calculated as 0.0699x10-3 mmol H2O2/L.sec in wastewater without dye. More then 90 % H2O2removal was achieved in 15 minutes with HRP-CLEA. The removal of the wastewater containing H2O2(0.02M) was completed in five minutes.In the scale-up approach, the data was evaluated using the Euler solution algorithm and the H2O2removal in the efficiency factor range where the kinetic constants change was calculated. Assuming the reaction rate changes linearly, the activity variations that will occur during scaling up with the enzyme in aggregate form were determined in the range of 125% -50%, and the industrial-scale design was modelled by taking into account the activity factors. In scaling up, concentrations that will occur in the increased reaction volume have been simulated. The results obtained showed that HRP-CLEAs are more advantageous than free enzyme in terms of time and cost.

SpyTag/Catcher chemistry is usually applied to engineer robust enzymes via head-to-tail cyclization using spontaneous intramolecular isopeptide bond formation. However, the SpyTag/Catcher induced intercellular protein assembly in vivo cannot be ignored. It was found that some active inclusion bodies had generated to different proportions in the expression of six SpyTag/Catcher labeled proteins (CatIBs-STCProtein). Some factors that may affect the formation of CatIBs-STCProtein were discussed, and the subunit quantities were found to be strongly positively related to the formation of protein aggregates. Approximately 85.44% of the activity of the octameric protein leucine dehydrogenase (LDH) was expressed in aggregates, while the activity of the monomeric protein green fluorescence protein (GFP) in aggregates was 12.51%. The results indicated that SpyTag/Catcher can be used to form protein aggregates in E. coli. To facilitate the advantages of CatIBs-STCProtein, we took the CatIBs-STCLDH as an example and further chemically cross-linked with glutaraldehyde to obtain novel cross-linked enzyme aggregates (CLEAs-CatIBs-STCLDH). CLEAs-CatIBs-STCLDH had good thermal stability and organic solvents stability, and its activity remained 51.03% after incubation at 60 °C for 100 mins. Moreover, the crosslinked CatIBs-STCLDH also showed superior stability over traditional CLEAs, and its activity remained 98.70% after 10 cycles of catalysis. [Display omitted] • Protein can be cross-linked intracellularly by fusing the label of SpyTag/Catcher. • Cross-linked proteins form aggregates named catalytically active inclusion bodies. • Aggregation rate of protein increases with the number of protein subunits. • Stability of aggregates was enhanced after cross-linking with glutaraldehyde. [ABSTRACT FROM AUTHOR]

The invertase enzyme has been immobilized onto various support materials to enhance operational stability, shelf life, and reusability compared to free ones. Among the immobilization methods, carrier-free immobilization, such as cross-linked enzyme aggregates (CLEAs), attracts attention. However, recovery of the CLEAs from the reaction environment by centrifugation or filtration is a great challenge. The use of magnetic nanoparticles (Fe3O4) can overcome these separation limitations of the aggregates. For this aim, in this study, the surface of magnetite nanoparticles was functionalized with a significant number of free amino groups through silanization reaction. After precipitation of these aggregates and then cross-linking to the functionalized structure, the resulting magnetite cross-linked invertase aggregates (MCLIAs) were obtained, having different enzyme and glutaraldehyde concentrations. Magnetic nanoparticles were characterized by SEM, VSM, and FTIR analysis. The assay parameters, both constructional and experimental ones on the activity of MCLIAs, were practically determined by a personal glucose meter (PGM). The results indicate that magnetite nanoparticles with superparamagnetic behaviour were successfully functionalized with amino groups. The activity results demonstrated that experimental parameters were more effective than constructional parameters. MCLIAs also exhibited maximum activity at pH 5. Furthermore, 30-min incubation time and 35 °C were the best activity assay conditions. [ABSTRACT FROM AUTHOR]

Laccases are versatile oxidases that are capable of decolorizing various synthetic dyes. Recombinant Bacillus amyloliquefaciens laccase was immobilized as magnetic cross-linked enzyme aggregates (M-CLEAs) for application in dye decolorization. Several parameters influencing the activity recovery were evaluated during the synthesis of M-CLEAs. With ammonium sulfate as precipitant, maximum activity was recovered by cross-linking with 0.16% glutaraldehyde for 1 h. The prepared M-CLEAs exhibited improved activity under alkaline conditions. It remained 74% activity after incubation at 60 °C for 5 h. Enhanced tolerance towards NaCl was also observed for the M-CLEAs, with 68% activity remaining in the presence of 1 M NaCl. The immobilized laccase could rapidly decolorize more than 93% of reactive black 5 and indigo carmine in 1 h, while its catalytic efficiency towards reactive blue 19 was relatively low. After four cycles of consecutive reuse, the M-CLEAs could decolorize 92% of indigo carmine. The easy recovery and reusability of M-CLEAs facilitate the potential application of bacterial laccase in dye decolorization. [ABSTRACT FROM AUTHOR]

Synthetic textile azo-dyes are important water contaminants in industrial textile wastes and peroxidases have potential for textile-dye degradation. The optimization of enzyme activity as crosslinked enzyme aggregases (CLEAs) without precipitant is important before use in any enzymatic process. In the proposed research, the immobilization of horseradish peroxidase in the form of crosslinked enzyme aggregates (HRP-CLEAs) without precipitant addition was optimized by three parameters full factorial experimental design at two levels and the degradation of an azo dye was tested. The optimal immobilization conditions were estimated as 0.06 mg enzyme/mL (0.96 U), 3 % (v/v, Glutaraldehyde)) cross-linker ratio, and 6 mg/mL Bovine Serume Albumine amount, respectively. The effects of variables were analysed by responce surface plots and the cross-linker ratio and albumin amount were found as important parameters while enzyme concentration effect was insignificant for the tested levels. The maximum CLEAs activity was 0.2188 U and the kinetic parameters (Km and Vmax) were 0.0314 mM and 0.1044 mM/min while the calculated values for soluble enzyme were 0.06 mM and 0.468 mM/min, respectively. It was estimated that hydrogen peroxide decreased the enzyme aggregate activities at higher amounts than 0.012 mM. Under optimal conditions, The HRP-CLEAs completely oxidised the textile azo dye, Reactive Blue 160 within 90 h and it was found that decolorization time of azo dye was shortened at higher temperatures. [ABSTRACT FROM AUTHOR]

α-Galactosidases hold immense potential due to their biotechnological applications in various industrial and functional food sectors. In the present study, soluble and covalently cross-linked aggregated forms of a low molecular weight, thermo-labile α-galactosidase from Vigna mungo (VM-αGal) seeds were immobilized onto chitosan-coated magnetic nanoparticles for improved stability and repeated usage by magnetic separation. Parameters like precipitants (type, amount, and ratio), glutaraldehyde concentration, and enzyme load were optimized for the preparation of chitosan-coated magnetic nanocomposites of cross-linked VM-αGal (VM-αGal-MC) and VM-αGal (VM-αGal-M) resulted in 100% immobilization efficiency. Size and morphology of VM-αGal-M were studied through dynamic light scattering (DLS) and scanning electron microscopy (SEM), while Fourier transform infrared spectroscopy (FTIR) was used to study the chemical composition of VM-αGal-MC and VM-αGal-M. VM-αGal-MC and VM-αGal-M were found more active in a broad range of pH (3–8) and displayed optimal temperatures up to 25 °C higher than VM-αGal. Addition of non-ionic detergents (except Tween-40) improved VM-αGal-MC activity by up to 44% but negatively affected VM-αGal-M activity. Both VM-αGal-MC (15% residual activity after 21 min at 85 °C, Ed 92.42 kcal/mol) and VM-αGal-M (69.0% residual activity after 10 min at 75 °C, Ed 39.87 kcal/mol) showed remarkable thermal stability and repeatedly hydrolyzed the substrate for 10 cycles. [ABSTRACT FROM AUTHOR]

A new design of cross-linked enzyme aggregates (CLEAs) of Burkholderia cepacia lipase (BCL) based mainly on the use of lignocellulosic residue of palm fiber as an additive was proposed. Different parameters for the preparation of active CLEAs in the hydrolysis of olive oil, such as precipitation agents, crosslinking agent concentration, additives, and coating agents were investigated. The highest activity yield (121.1 ± 0.1%) and volumetric activity (1578.1 ± 2.5 U/mL) were achieved for CLEAs prepared using the combination of a coating step with Triton® X-100 and polyethyleneimine plus the use of palm fiber as an additive. The variations of the secondary structures of BCL-CLEAs were analyzed by second-derivative infrared spectra, mainly indicating a reduction of the α-helix structure, which was responsible for the lipase activation in the supramolecular structure of the CLEAs. Thus, these results provided evidence of an innovative design of BCL-CLEAs as a sustainable and biocompatible opportunity for biotechnology applications. [ABSTRACT FROM AUTHOR]

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• Optimal design of magnetite cross-linked tyrosinase aggregates was firstly presented. • Multiple nonlinear neuro-regression analysis was performed. • Realistic functional structures were obtained by examining the models. • Deceptive results could be eliminated by this optimization approach. • This novel approach is feasible for another modeling-design-optimization problems. In this study, a new design strategy with a systematic optimization process is proposed for the preparation of magnetite cross-linked tyrosinase aggregates (MCLTA) by using the concentration of magnetite nanoparticle, glutaraldehyde and tyrosinase enzyme as design variables. A comprehensive study on multiple non-linear neuro-regression analysis has been performed as a compelling alternative to the insufficient approaches on modeling-design-optimization of MCLTA. For this aim, the experimental process has been modeled with 13 candidate functional structures by using a hybrid method to test the accuracy of their predictions. R2 training , R2 testing values, and boundedness of the functions have been checked to reveal the realistic ones. Then four different design approaches in terms of three distinct scenarios have been used to optimize the process. The results show that, all models define the process well, depending on R2 training. However, only five and nine models are appropriate based on R2 testing for the first use activity and residual activity, respectively. On the other hand, depending on to be a realistic value, model TON best describes the "first use activity," while the best one is FONT for residual activity. It is also concluded that the scenario types and selection of constraints for design variables affect the optimization results. [ABSTRACT FROM AUTHOR]

Transaminases are a class of enzymes with promising applications for the preparation and resolution of a vast diversity of valued amines. Their poor operational stability has fueled many investigations on its stabilization due to their biotechnological relevance. In this work, we screened the stabilization of the tetrameric ω-transaminase from Pseudomonas fluorescens (PfωTA) through both carrier-bound and carrier-free immobilization techniques. The best heterogeneous biocatalyst was the PfωTA immobilized as cross-linked enzyme aggregates (PfωTA-CLEA) which resulted after studying different parameters as the precipitant, additives and glutaraldehyde concentrations. The best conditions for maximum recovered activity (29 %) and maximum thermostability at 60 ºC and 70 ºC (100 % and 71 % residual activity after 1 h, respectively) were achieved by enzyme precipitation with 90% acetone or ethanol, in presence of BSA (100 mg/mL) and employing glutaraldehyde (100 mM) as cross-linker. Studies on different conditions for PfωTA-CLEA preparation yielded a biocatalyst that exhibited 31 and 4.6 times enhanced thermal stability at 60 °C and 70 °C, respectively, compared to its soluble counterpart. The PfωTA-CLEA was successfully used in the bioamination of 4-hydroxybenzaldehyde to 4-hydroxybenzylamine. To the best of our knowledge, this is the first report describing a transaminase cross-linked enzyme aggregates as immobilization strategy to generate a biocatalyst with outstanding thermostability. Unlabelled Image • P. fluorescens ω-transaminase (PfωTA) was immobilized via several strategies. • PfωTA cross-linked aggregates were the most stable immobilized biocatalysts. • Outstanding thermal and operational stabilization of PfωTA was successfully achieved. • PfωTA biocatalysts were employed in the bioamination of aldehydes. • Preparation of self-sufficient biocatalysts by co-immobilization of PLP and PfωTA as CLEA [ABSTRACT FROM AUTHOR]

With proper design, immobilization can be useful tool to improve the stability of enzymes, and in certain cases even their activity, selectivity, productivity and economic viability. An immobilized β-glucosidase (BGL, EC 3.2.1.21) through matrix adsorption and cross-linked enzyme aggregate (ad-CLEA) technology is presented in this work. After adsorption and precipitation, BGL was immobilized to poly(glycidyl methacrylate-co-ethylenedimethacrylate) (PGMA/EDMA) microparticles using glutaraldehyde as the cross-linker. Immobilized BGL exhibits lower apparent Km but much higher Vmax than that of the soluble enzyme, suggesting greater enzyme–substrate affinity and rapid velocity. Besides, ad-CLEA-BGL presents better thermostability retaining activity nearly 70% for 3 h and approximately 50% for 5 h at 70 °C, high operational reusability remaining more than 90% activity after nine uses and excellent storage stability holding about 95% activity after 45 days. Furthermore, the cellobiose is completely hydrolyzed within 1 h with ad-CLEA-BGL, which is significantly more efficient than soluble enzyme (about 4 h). Therefore, BGL was successfully immobilized on PGMA/EDMA microparticles with an ad-CLEA technology and the immobilization greatly enhances the biochemical characteristics. This work indicates promising application for ad-CLEA-BGL in utilizing agricultural remnants, bio-converting cellobiose to fermentable reducing sugar and ethanol production. [ABSTRACT FROM AUTHOR]

ß-galactosidases from Lactobacillus leichmannii 313 (LL 313) were immobilized for the first time by cross-linked enzyme aggregates (CLEA) technology. By using three precipitants (saturated ammonium sulfate (ASF), acetone (ACT), and isopropanol (IPA) in CLEA preparation and assessing performance in comparison with crude enzyme, recovered activities of 23% (ASFCLEA), 18% (ACT-CLEA), 13.6% (IPA-CLEA) were obtained. Immobilization did not change the optimal pH (7.0) and temperature (55 °C), except for ACT-CLEA (60 °C). CLEA retained activity ( -- 90% for ASF-CLEA) after 2 weeks storage at 4 °C in buffer; and for ACT-CLEA and IPACLEA, -- 50% of initial activity was retained after 10 cycles of use. Plackett-Burman (PB) and Response Surface Methodology (RSM) optimization with ASF as precipitant gave 23.5 mM of glutaraldehyde, reaction pH 6.9 and reaction time of 3.4 h as the optimum conditions giving highest recovered activity of 37.7%. The kinetics (Vmax and Km) were 0.06 mmol g-1 min-1 and 4.95 mM respectively for ASF-CLEA, compared with 0.0/ mmol g'1 min 1 and 4.08 iriM for crude enzyme. All CLEA types exhibited the capability to hydrolyze lactose and generate GOS. This study shows that CLEA is a suitable technique to immobilize ß-galactosidase from LL313, and the resulting enzyme system has promising applications in the food industry. © 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. [ABSTRACT FROM AUTHOR]

Short-chain fructooligosaccharides (scFOSs) can be produced from the levan hydrolysis using levanase. Levanase from Bacillus lehensis G1 (rlevblg1) is an enzyme that specifically converts levan to scFOSs. However, the use of free levanase presents a lack of stability and reusability, thus hindering the synthesis of scFOSs for continuous reactions. Here, CLEAs for rlevblg1 were prepared and characterized. Cross-linked levanase aggregates using glutaraldehyde (CLLAs-ga) and bovine albumin serum (CLLAs-ga-bsa) showed the best activity recovery of 92.8% and 121.2%, respectively. The optimum temperature of CLLAs-ga and CLLAs-ga-bsa was increased to 35 °C and 40 °C, respectively, from its free rlevblg1 (30 °C). At high temperature (50 °C), the half-life of CLLAs-ga-bsa was higher than that of free rlevblg1 and CLLAs-ga. Both CLLAs exhibited higher stability at pH 9 and pH 10. Hyperactivation of CLLAs-ga-bsa was achieved with an effectiveness factor of more than 1 and with improved catalytic efficiency. After 3 h reaction, CLLAs-ga-bsa produced the highest total scFOSs yield of 35.4% and total sugar of 60.4% per gram levan. Finally, the reusability of CLLAs for 8 cycles with more than 50% activity retained makes them as a potential synthetic catalyst to be explored for scFOSs synthesis. Unlabelled Image • Cross-linked levanase aggregates using glutaraldehyde (CLLAs-ga), and BSA as an additive (CLLAs-ga-bsa) were prepared. • CLLAs-ga-bsa resulted in 121.2 % activity as opposed to 92.8 % for CLLAs-ga. • CLLAs-ga-bsa demonstrated higher thermal stability and strong bonding stability. • The hyperactivation of CLLAs-ga-bsa is due to a high effectiveness factor with improved catalytic efficiency. • CLLAs-ga-bsa synthesized 35.4 % of scFOSs and 60.4 % of total sugar per gram of levan. [ABSTRACT FROM AUTHOR]

• Feruloyl esterases (FAE) low stability in solvents challenges its use in synthesis. • FAE A from A. niger was successfully immobilized in epoxy activated supports and CLEA. • CLEA with BSA as cofeeder and 15 mM glutaraldehyde was the most active biocatalyst. • CLEA attained complete butyl sinapate solvent free esterification within 24 h. • CLEA performed 10 esterification cycles without significant loss of activity. Feruloyl esterases synthesize butyl hydroxycinnamates, molecules possessing interesting biological properties, nonetheless, they exhibit a low stability under synthesis conditions in organic solvents, restricting its use. To enhance its operational stability in synthesis, we immobilized type A feruloyl esterase from Aspergillus niger (AnFAEA) using several carrier-bound and carrier-free strategies. The most active biocatalysts were: 1) AnFAEA immobilized on epoxy-activated carriers (protein load of 0.6 mg enzyme x mg−1 carrier) that recovered 91 % of the initial hydrolytic activity, and 2) AnFAEA aggregated and cross-linked in the presence of 5 mg of BSA and 15 mM of glutaraldehyde (AnFAEA-amino-CLEAs), which exhibited 385 % of its initial hydrolytic activity; both using 4-nitrophenyl butyrate as substrate. The AnFAEA-amino-CLEAs were 12.7 times more thermostable at 60 °C than the AnFAEA immobilized on epoxy-activated carrier, thus AnFAEA-amino-CLEAs were selected for further characterization. Interestingly, during methyl sinapate hydrolysis (pH 7.2 and 30 °C), AnFAEA-amino-CLEAs K M was 15 % higher, while during butyl sinapate synthesis the K M was reduced in 63 %, both compared with the soluble enzyme. The direct esterification of butyl sinapate at solvent free conditions using sinapic acid 50 mM, reached 95 % conversion after 24 h employing AnFAEA-amino-CLEAs, which could be used for 10 cycles without significant activity losses, demonstrating their outstanding operational stability. [ABSTRACT FROM AUTHOR]

This study focuses on well-known but commonly overlooked or unreported factors in the preparation of cross-linked enzyme nano-aggregates (nano-CLEAs). The parameters including the ionic strength of the protein solution, protein, precipitant and cross-linker concentrations, pH and addition order of the reagents were fine-tuned for nanoaggregate preparation without the need of non-protein support material, special equipment or sophisticated procedures. For this purpose, precipitation as nano-aggregates and then cross-linking while maintaining submicron size distribution were studied independently. Moreover, nano-aggregate formation from reverse micellar solutions was also investigated to improve the scope of the method to membrane-bound enzymes. Five different precipitation agents together with three different cross-linkers were investigated for immobilization of the Trametes versicolor laccase as cross-linked nano-aggregates. Although complete activity recovery was possible for micro-aggregates, the best activity results for nano-aggregates were 40.5%±5.0. The Km values of the immobilized enzymes were slightly lower than the Km values of the free counterparts which indicate little or no mass transfer limitation due to the nano-immobilization process. However, Vmax values were also lower. The activity loss and Vmax reduction upon immobilization were found to mainly result from the modification of the amine groups instead of excess crosslinking. The thermal stabilities of the crosslinked laccase nano-aggregates were significantly higher (∼10–30 fold at 60 °C) compared to free laccase and the nano-CLEAs retained up to 30% of their initial activities upon 7 consequent usages. The sizes of the obtained immobilized enzyme products were found to be greatly variable depending on the cross-linker type. The smaller particles (∼200 nm radius) were obtained when EDAC was used as the cross-linker. The larger products (∼600 nm radius) were prepared when the cross-linker was dextran poly-aldehyde. The addition order of the reagents was found to be effective on particle size and thermal stability values. [ABSTRACT FROM AUTHOR]

BACKGROUND: Cross‐linked enzyme aggregates (CLEAs) of α‐galactosidase, partially purified from maize (Zea mays) flour, were prepared. The impact of various parameters on enzyme activity was examined to optimize the immobilization procedure. Biochemical characterization of the free and immobilized enzyme was carried out. Stability (thermal, pH, storage and operational stability) and reusability tests were performed. The potential use of the free enzyme and the CLEAs in hydrolysis processes of raffinose‐type oligosaccharides present in soymilk was investigated. RESULTS: α‐galactosidase CLEAs were prepared with 47% activity recovery under optimum conditions [1:5 (v/v) enzyme solution:saturated ammonium sulfate solution ratio; 7.5 mg protein and 0.1% (v/v) glutaraldehyde, 6 h, 4 °C, 150 rpm]. α‐galactosidase CLEAs exhibited increased stability in comparison to the free enzyme. The CLEAs and the free enzyme showed a maximum activity at 40°C and their optimal pH values were5.5 and 6.0, respectively. Kinetic constants (KM, Vmax and kcat) were calculated for the free enzyme and the CLEAs in the presence of p‐nitrophenyl‐α‐d‐galactopyranoside, stachyose, melibiose and raffinose. The effect of various chemicals and sugars on enzyme activity showed that both enzyme forms were significantly inhibited by HgCl2 and galactose. The CLEAs hydrolyzed 85% of raffinose and 96% of stachyose. CONCLUSION: The α‐galactosidase CLEAs, with their satisfactory enzymatic characteristics, have much potential for use in the food and feed industry. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The current industrial revolution signifies the high-value of protein engineering. The development of multipurpose biocatalysts is significantly expanding as a result of increased access and enzyme tailoring ability to satisfy the ever-increasing industrial demands. Enzyme-catalyzed processes offers multi-benefits at a time, e.g., low catalyst loading, high specificity, selectivity, mild processing for a complex and chemically unstable compounds, capability to reduce or eliminate reaction by-products, overall reusability and cost-effective ratio via immobilization, and potential to carry out conventional multi-stage processes via one-pot reaction. In this review, we critically elaborated recent achievements in applying new and/or state-of-the-art sophisticated protein engineering approaches to tailor the catalytic properties of enzymes or design enzymes with new and improved activities to catalyze desired biochemical transformations by orders of magnitude. We focused on different protein engineering approaches such as substrate engineering, medium engineering, and post-translational enzyme modification, structure-assisted protein tailoring, advanced computational modeling, and the exploration of inimitable synthetic scaffolds to develop multipurpose biocatalyst and improve the performance of multi-enzyme systems. In short, this study demonstrates an array of molecular biology insights and computational designs speeding up the tailored design of new and industrial biocatalysts. Continuous key developments in this direction together with protein engineering in unique ways might offer the ever-increasing opportunities for impending biocatalysis research for industrial bioprocesses. [ABSTRACT FROM AUTHOR]

Lipase r27RCL from Rhizopus chinensis was immobilized onto octyl-modified mesocellular foams (MCFs-C8) via two-step process of enzyme adsorption and cross-linking. Oxidized gum arabic was used as substitute for harmful glutaraldehyde to improve catalytic performance of immobilized enzyme for catalysis in non-aqueous phase. The parameters like aldehyde concentration, cross-linking time were optimized. Cross-linked enzyme aggregates (CLEAs) of lipase r27RCL prepared in MCFs-C8 by using oxidized gum arabic (GA-CLEAs@MCFs-C8) showed the highest esterification activity (145 μmol min−1 mg−1 protein) compared with lipase adsorbed onto MCFs-C8 (MCFs-C8-r27RCL) (98 μmol min−1 mg−1 protein), CLEAs of lipase in MCFs-C8 by glutaraldehyde (G-CLEAs@MCFs-C8) (88 μmol min−1 mg−1 protein) and immobilized lipase onto octyl/epoxy (1,1, v/v) modified MCFs (MCFs-octyl-epoxy-r27RCL) (35 μmol min−1 mg−1 protein). Moreover, GA-CLEAs@MCFs-C8 exhibited excellent thermal and mechanical stability, and could still maintain 69% of initial activity after 5 time cycles. [ABSTRACT FROM AUTHOR]

In the present study, Candida antarctica lipase B was immobilized on amine‐functionalized silica microspheres as cross‐linked enzyme aggregates (CLEA) and utilized for the biomanufacturing of rhamnolipids (RL). Lipase CLEA synthesized under optimized conditions of 2.0:1.0 by volume of silica microsphere/enzyme concentration, a 1.0:2.5 (v/v) ratio of enzyme/2‐propanol, 7 mM glutaraldehyde concentration, when incubated at pH 9.0 and 40 °C, for a cross‐linking time of 30 min were observed to exhibit superior biocatalytic properties and a maximum enzyme load of 770 U g−1. Lipase CLEA exhibited enhanced pH stability in acidic and alkaline media and increased temperature resistance as compared to free lipase. Both free and CLEA lipases were used to synthesize RL in different solvent systems. After 12 h, from initiation of the esterification, the degree of esterification (molar conversion yield) reached 46% and 71% in the batch mode. 1H and 13C nuclear magnetic resonance (NMR) and high‐performance liquid chromatographic (HPLC) analysis confirm RL production by CLEA lipase. The CLEA showed greater confrontation to enzyme‐mediated bioprocess approach as compared to its soluble counterpart and exhibited excellent RL production and catalytic activity even after its tenth successive reuse. [ABSTRACT FROM AUTHOR]

BACKGROUND: High‐purity α‐, β‐, or γ‐cyclodextrin (CD) production using cyclodextrin glycosyltransferase (CGTase) as biocatalyst to cyclize starch is advantageous owing to its low cost of purification and product specificity. Several approaches have been investigated to enhance product specificity of CGTase, such as new CGTase isolation, CGTase gene (cgt) mutation, and chemical addition. RESULTS: Recombinant CGTase was cross‐linked by glutaraldehyde to obtain cross‐linked enzyme aggregates of recombinant CGTase (CLEA‐CGTase) at 85 °C because free CGTase showed high product specificity at 85 °C. The CLEA‐CGTase was prepared under the conditions 75 U mL−1 CGTase with 0.1% (v/v) glutaraldehyde for 10 min at 85 °C after optimization first, and produced a high proportion of β‐CD from soluble starch at 50 °C in the conversion system. The conversion process was carried out with 10 to 200 U mL−1 CLEA‐CGTase, resulting in 100% β‐CD from soluble starch after 420 min conversion of the potato starch solution at 50 °C. And the proportion of β‐CD was still higher than 90% when 8000 U mL−1 CLEA‐CGTase was added. CONCLUSIONS: CLEA technology maintained CGTase conformation of 85 °C, and produced a high proportion of β‐CD at 50 °C. This research showed the CLEA technology kept the conformation of enzyme for specific product production. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The present study focusses on the enhancement of the catalytic activity and stability of an acetylesterase enzyme isolated from Staphylococcus spp. as Cross-Linked Enzyme Aggregates (CLEAs). The various parameters governing the activity of CLEAs were optimized. The magnetite and graphene oxide nanoparticles were successfully prepared via the chemical co-precipitation and Hummer's method, respectively. These nanoparticles supported the preparation as magnetite nanoparticle-supported cross-Linked Enzyme Aggregates (MGNP-CLEAs) and graphene oxide-supported Cross-Linked Enzyme Aggregates (GO-CLEAs). The activity and stability of these immobilized CLEAs were compared with the free enzyme at various temperature, pH, and organic solvents along with its storage stability and reusability. The immobilized preparations were analyzed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectroscopy (FT-IR) techniques. Acetylesterase precipitated with 60% saturated ammonium sulfate salt (SAS) solution and cross-linked with 100 mM glutaraldehyde for 4 h at 30 °C was found to be optimal to produce CLEAs with highest activity recovery of 99.8%. The optimal pH at 8.0 and temperature at 30 °C remained the same for both the free and immobilized enzyme, respectively. Storage stability significantly improved for the immobilized enzyme as compared to free enzyme. SEM showed type-I aggregate and FT-IR revealed the successful immobilization of the enzyme. MGNP-CLEAs were found to have better activity and stability in comparison to other immobilized preparations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Preparation and characterization of CLEA- Bm HNL reported first time. • Reusability of CLEA- Bm HNL in (S)-cyanohydrin synthesis up to eight cycles without loss of conversion. • CLEA has improved enantioselectivity of (S)-cyanohydrin synthesis compared to the use of purified enzyme. • Among the 11 (S)-cyanohydrins synthesized here, 8 were not synthesized by any CLEA-HNL and 9 were not tested by BmHNL earlier. Abstract Hydroxynitrile lyase (HNL) catalyzed enantioselective C C bond formation is an efficient approach to synthesize chiral cyanohydrins which are important building blocks in the synthesis of a number of fine chemicals, agrochemicals and pharmaceuticals. Immobilization of HNL is known to provide robustness, reusability and in some cases also enhances activity and selectivity. We optimized the preparation of immobilization of Baliospermium montanum HNL (Bm HNL) by cross linking enzyme aggregate (CLEA) method and characterized it by SEM. Optimization of biocatalytic parameters was performed to obtain highest % conversion and ee of (S)-mandelonitrile from benzaldehyde using CLEA- Bm HNL. The optimized reaction parameters were: 20 min of reaction time, 7 U of CLEA- Bm HNL, 1.2 mM substrate, and 300 mM citrate buffer pH 4.2, that synthesized (S)-mandelonitrile in ∼99% ee and ∼60% conversion. Addition of organic solvent in CLEA- Bm HNL biocatalysis did not improve in % ee or conversion of product unlike other CLEA-HNLs. CLEA- Bm HNL could be successfully reused for eight consecutive cycles without loss of conversion or product formation and five cycles with a little loss in enantioselectivity. Eleven different chiral cyanohydrins were synthesized under optimal biocatalytic conditions in up to 99% ee and 59% conversion, however the % conversion and ee varied for different products. CLEA- Bm HNL has improved the enantioselectivity of (S)-mandelonitrile synthesis compared to the use of purified Bm HNL. Nine aldehydes not tested earlier with Bm HNL were converted into their corresponding (S)-cyanohydrins for the first time using CLEA- Bm HNL. Among the eleven (S)-cyanohydrins syntheses reported here, eight of them have not been synthesized by any CLEA-HNL. Overall, this study showed preparation, characterization of a stable, robust and recyclable biocatalyst i.e. CLEA- Bm HNL and its biocatalytic application in the synthesis of different (S)-aromatic cyanohydrins. [ABSTRACT FROM AUTHOR]

Abstract In this study, polyvinyl alcohol (PVA)-degrading bacteria were screened from sludge samples using PVA as a sole source of carbon. A novel strain was obtained and identified as Bacillus niacini based on the analysis of a partial 16S rDNA nucleotide sequence and morphological characteristics. PVA-degrading enzyme (PVAase) from Bacillus niacini was immobilized as cross-linked enzyme aggregates (CLEAs) via precipitation with ammonium sulfate followed by glutaraldehyde cross-linking. The effects of precipitation and cross-linking on PVAase-CLEAs activity were investigated and characterized. 70% ammonium sulfate and 1.5% glutaraldehyde were used for precipitation and 1-h cross-linking reaction. The activity recovery of PVAase-CLEAs was approximately 90% starting from free PVAase, suggesting non-purification steps are required for extended use. No significant differences in optimum pH and temperature values of the PVAase were recorded after immobilization. The PVAase-CLEAs showed a ball-like morphology and enhanced PVA degradation efficiency in comparison with the free PVAase in solution. Furthermore, the PVAase-CLEAs exhibited excellent thermal stability, pH stability and storage stability compared to free PVAase. The PVAase-CLEAs retained about 75% of initial PVAase activity after 4 cycles of use. These results suggest that this CLEA is potentially usable for PVA degradation in industrial applications. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

α-Galacto-oligosaccharides (α-GOSs) have great functions as prebiotics and therapeutics. This work established the method of batch synthesis of α-GOSs by immobilized α-galactosidase for the first time, laying a foundation for industrial applications in the future. The α-galactosidase from Aspergillus niger L63 was immobilized as cross-linked enzyme aggregates (CLEAs) nano-biocatalyst through enzyme precipitating and cross-linking steps without using carriers. Among the tested agents, the ammonium sulfate showed high precipitation efficacy and induced regular structures of α-galactosidase CLEAs (Aga-CLEAs) that had been analyzed by scanning electron microscopy and Fourier-transform infrared spectroscopy. Through optimization by response surface methodology, the ammonium sulfate-induced Aga-CLEAs achieved a high activity recovery of around 90% at 0.55 U/mL of enzymes and 36.43 mM glutaraldehyde with cross-linking for 1.71 h. Aga-CLEAs showed increased thermal stability and organic solvent tolerance. The storage ability was also improved since it maintained 74.5% activity after storing at 4 °C for three months, significantly higher than that of the free enzyme (21.6%). Moreover, Aga-CLEAs exhibited excellent reusability in the α-GOSs synthesis from galactose, retaining above 66% of enzyme activity after 10 batch reactions, with product yields all above 30%.

Phenylalanine ammonia lyase (PAL) is a key enzyme for production of L-phenylalanine. Currently, PAL is mainly obtained from Rhodotorula PAL However, Rhodotorula PAL exhibits poor stability, which limits its industrial application. In this study, bioimprinting cross-linked enzyme aggregates of PAL (PAL-iCLEAs) is developed by combining cross-linked enzyme aggregates technology and imprinted enzyme method. The most optimal imprinting molecule substrate is screened. Moreover, some characteristics of the PAL-iCLEAs are examined. The results show that the most suitable substrates for preparing PAL-iCLEAs is tran-cinnamic acid. The optimal temperature and pH was 50 ℃ and 10.5, respectively. In addition, PAL-iCLEAs shows good reusability, the recovery of PAL activity still remained 32% after reusing 9 times.

In this study, phenylalanine ammonia lyase (PAL) is used as model, and the cross-linked enzyme aggregates of PAL with crude-pored microspherical silica core (NH-PAL-CLEAs) are prepared. The conditions for the preparation of NH-PAL-CLEAs are optimized. Moreover, some characteristics of the NH-PAL-CLEAs are examined. The optimized conditions for preparing NH-PAL-CLEAs are as follows: 117.75 mg silica, 0.2% (v/v) glutaraldehyde and 1 mL free PAL solution (2 U). Under optimized conditions, the maximum activity recovery of NH-PAL-CLEAs reaches 25%. Compared with PAL-CLEAs, the resulting NH-PAL-CLEAs can be easily separated from the reaction mixture by natural precipitation without centrifugation and filtration treatments. Moreover, NH-PAL-CLEAs show superior operational stability. This technique not only overcomes the difficulty to recover CLEAs due to their small particle sizes and soft for many industrial applications, but also reduces production cycle and energy consumption. As a result, this technique shows superior application prospect for enzyme immobilization.

Abstract Lignocellulosic biomass, packed with sugars, is one of the most available renewable resources for biofuels and bioproducts production. To release the sugars for the production, enzymatic hydrolysis (saccharification) of pretreated lignocellulosic biomass are required. However, the saccharification process is costly, inefficient, and requires multi-step operations. This is in part due to the high cost and the limited selection of commercial enzymes which commonly have different optimal pH and temperatures. Here we reported a one-step saccharification of pretreated lignocellulosic biomass using immobilized biocatalysts containing five different saccharifying enzymes (SEs) with a similar optimum pH and temperature. The five SEs - endo-1,4-β- d -glucanase (an endoglucanase, eglS), cellobiohydrolase (an exoglucanase, cbhA), and β-glucosidase (bglH), endo-1,4-β-xylanase (an endoxylanase, xynC) and β-xylosidase (bxlB) – were successfully expressed and produced by E. coli BL21. Better saccharification of pretreated corn husks was observed when using the five crude SE enzymes than those using two commonly used SEs, endo-1,4-β- d -glucanase and β-glucosidase. The five SEs were cross-linked in the absence or the presence of magnetic nanoparticles (hereafter referred as SE-CLEAs and M-SE-CLEAs, respectively). By using SE-CLEAs, the highest amount of reduced sugar (250 mg/g biomass) was measured. The activity of immobilized SEs is better than free crude SEs. The M-SE-CLEAs can be reused at least 3 times for effective saccharification of pretreated lignocellulosic biomass. Graphical abstract Unlabelled Image Highlights • Saccharifying enzymes (SEs) with similar optimal pH and temperature were produced. • The produced SEs enabled a simple one-step enzymatic hydrolysis. • Using the SEs resulted in 100% more sugar release than using commercial cellulases. • Higher amounts of reduced sugar were observed using immobilized SEs than crude SEs. • Magnetic-cross-linked enzyme aggregates allow for rapidly recover and reuse of SEs. [ABSTRACT FROM AUTHOR]

A thermo-stable purified serine hydroxymethyltransferase (SHMT; 418 AA) was used for the carrier free immobilization using pectin as a coach molecule and formaldehyde as a cross-linker. The purified protein was cross linked with formaldehyde in the presence of pectin to form stable and active aggregates. The cross-linked enzyme aggregates [CLEAs] of SHMT showed improved catalytic properties and reusability. The SHMT-CLEAs showed a noteworthy change in the thermo-stability and activity compared to its free counterpart. The optimum activity for free SHMT was reported at 55 °C and pH 7.5 which SHMT CLEAs showed maximum activity at 60 °C and pH 8.0. Similarly, the CLEAs were noticed to increase the thermo-stability in comparison to free enzyme. The divalent salt ion Ca 2+ and Ba 2+ were found to enhance the activity at 1 and 5 mM of concentrations while Ni + , Co 2+ and Zn 2+ strongly inhibited the activity of both free as well as CLEAs. The V max and k m values for free SHMT were recorded to be 1.21 μM s −1 and 272 μM while for CLEAs V max 1.42 μM s −1 and k m 248.6 μM was recorded. Thus, a 120% increase in the V max was recorded for SHMT-CLEAs. The CLEAs were also found to be more stable at pH 6.5 and 8.5 pHs and retained 50% of its original activity for 180 and 200 min respectively. The CLEAs also retained 72% of its activity after 12 repetitive cycles of d -phenylserine hydrolysis. Also, the synthesized CLEAs retained more than 60% of its original activity after 10 days of incubation at 25 °C in comparison to free enzyme which loses more than 90% of its residual activity. Thus, with improved thermostability and activity the CLEAs of SHMT can be used repetitively at industrial scale for the synthesis of commercially important amino acids. [ABSTRACT FROM AUTHOR]

Development of industrially potent cellulolytic enzymes is one of the greatest challenges faced in lignocellulosic feed-stock based bio-refining. In the current work cross-linked enzyme aggregates (CLEAs) of commercial cellulase mix were successfully prepared and their performance to be used as potential industrial enzymes in terms of stability and wheat straw hydrolysis was evaluated. The CLEAs were more stable compared to native enzymes with half-lives being 2.30-, 1.56-, 3.07- and 1.67-fold higher at 70°C for filter paper activity (FPA), endoglucanase, β-glucosidase and xylanase, respectively. CLEAs retained 77.4% of endoglucanase and 85.9% of xylanase activity after five cycles of hydrolysis of soluble substrates such as carboxymethyl cellulose and xylan, respectively. A maximum saccharification yield of 31.8% by soluble enzymes and 32.9% by CLEAs were obtained when alkali-pretreated wheat straw was subjected to hydrolysis. On repeated batch hydrolysis for five consecutive cycles of 24 h each, the CLEAs showed an overall higher saccharification yield of 43.3% compared to 31.8% with soluble enzymes. Highlights • Cross-linked enzyme aggregates of cellulolytic enzymes were prepared. • The kinetic and stability parameters of the best CLEA were determined. • The best CLEA was more effective in hydrolysing wheat straw. • It resulted in overall saccharification yield of 43.3% compared to 31.8% with soluble enzymes. [ABSTRACT FROM AUTHOR]

In order to increase application of cross-linked enzyme aggregates (CLEAs) in industry production, a novel micro-reactor system that included a rotating magnetic field (RMF), a micro-reactor and CLEAs with magnetic nanoparticles (M-CLEAs) was designed to synthesize butyl oleate. Result showed that the presence of RMF significantly increased the yield of butyl oleate and the maximum increment was 23%. The yield of butyl oleate was impacted by the dosage and distribution of M-CLEAs in micro-reactor. M-CLEAs showed good reusability, since the morphology and the second structure of protein of M-CLEAs did not show evident change after 4 operative cycles. Although the three-dimensional fluorescence of M-CLEAs showed shift in fluorescence intensity and the maximum emission wavelengths, the yield of butyl oleate was not affected. This study provides a novel design that realized efficient, convenient and continuous application of CLEAs in biosynthesis, and M-CLEAs also show good promises in industry production. [ABSTRACT FROM AUTHOR]

Feruloyl esterases (FAEs, E.C. 3.1.1.73) are biotechnologically important enzymes with several applications in ferulic acid production from biomass, but also in synthesis of hydroxycinnamic acid derivatives. The use of such biocatalysts in commercial processes can become feasible by their immobilization, providing the advantages of isolation and recycling. In this work, eight feruloyl esterases, immobilized in cross-linked enzyme aggregates (CLEAs) were tested in regard to their transesterification performance, towards the production of prenyl ferulate (PFA) and arabinose ferulate (AFA). After solvent screening, comparison with the activity of respective soluble enzymes, and operational stability tests, FAE125 was selected as the most promising biocatalyst. A central composite design revealed the optimum conditions for each transesterification product, in terms of water content, time, and substrate ratio for both products, and temperature and enzyme load additionally for prenyl ferulate. The optimum product yields obtained were 83.7% for PFA and 58.1% for AFA. FAE125 CLEAs are stable in the optimum conditions of transesterification reactions, maintaining 70% residual activity after five consecutive reactions. Overall, FAE125 CLEAs seem to be able to perform as a robust biocatalyst, offering satisfactory yields and stability, and thus showing significant potential for industrial applications. [ABSTRACT FROM AUTHOR]

Cross-linked enzyme aggregate (CLEA) methodology has been applied to immobilize cytochrome P450 BM3 variants (F87A and 21B3) with peroxygenase activity. Several Ru(II)-diimine complexes were found to be suitable cross-linking agents, surpassing the traditional glutaraldehyde and dextran aldehyde. They offer modular numbers of aldehyde functionalities and a more rigid framework than their organic counterparts. The F87A CLEAs display significant activity loss compared to the protein in solution. Meanwhile, for the 21B3 CLEAs, high activity recovery (up to 95%) is obtained. In order to minimize enzyme leaching from the CLEA, sodium cyanoborohydride was used to reduce the CLEAs imine bonds. The reduced CLEAs were active for several rounds of reactions leading to an overall increase in protein activity of 170% compared to the free protein in solution. [ABSTRACT FROM AUTHOR]

We describe the development of cross-linked enzyme aggregates (CLEA) of dextransucrase of Leuconostoc mesenteroides B-512 F. Treatments of enzyme preparation using dextranase were evaluated varying incubation time to remove the dextran layer involving the enzyme molecule, turning it suitable for immobilization. Results showed 21 days of treatment as the best outcome. Subsequently, we tested different water-miscible organic solvents as precipitants, the reaction and centrifugation times, and the concentration of cross-linker agent (glutaraldehyde) in the preparation of CLEA. Optimal conditions were: the use of isopropanol as solvent, 30 min of centrifugation time, 3 h of cross-linking time, and 100 mM of glutaraldehyde. A central composite design was carried out to optimize conditions to obtain the highest enzymatic activity, testing the pH (3.0–7.0) and temperature (20 °C-60 °C). Results showed that dextransucrase CLEA operate at optimal pH of 3.0 and temperature of 60 °C. The operational stability of the immobilized biocatalyst showed up to 30% of residual activity after 10 cycles of reuse, in a solution of 100 mM of sucrose and 600 mM of maltose. The preparation of dextransucrase CLEA is described for the first time and results suggest that this novel immobilized biocatalyst has potential in many industrial applications. [ABSTRACT FROM AUTHOR]

Ligninolytic enzymes from white-rot fungi are widely used in biotechnological processes. However, the application of these enzymes as free enzymes is limited due to their instability and lack of reusability. Enzyme stabilization is therefore a major challenge in biocatalytic process research, and immobilization methods are desirable. Using cross-linked enzyme aggregates (CLEAs) such as magnetic CLEAs, porous-CLEAs and combi-CLEAs is a promising technique for overcoming these issues. Cross-linking methods can stabilize and immobilize enzymes by interconnecting enzyme molecules via multiple bonds using cross-linking agents such as glutaraldehyde. The high catalyst density and microporous assembly of CLEAs guarantee high catalyst activity, which, together with their long shelf life, operational stability, and reusability, provide a cost-efficient alternative to matrix-assisted immobilization approaches. Here, we review current progress in ligninolytic enzyme immobilization and provide a comprehensive review of CLEAs. Moreover, we summarize the use of these CLEAs for biocatalysis processes, bioremediation such as dye decolourization, wastewater treatment or pharmaceutically active compound elimination. [ABSTRACT FROM AUTHOR]