Optimizing the preparation conditions and characterization of a stable and recyclable cross-linked enzyme aggregate (CLEA)-protease

Extended Biocatalytic Halogenation Cascades Involving a Single-Polypeptide Regeneration System for Diffusible FADH2

Flavin-dependent halogenases have attracted increasing interest for aryl halogenation at unactivated C-H positions because they are characterised by high regioselectivity, while requiring only FADH2 , halide salts, and O2 . Their use in combined crosslinked enzyme aggregates (combiCLEAs) together with an NADH-dependent flavin reductase and an NADH-regeneration system for the preparative halogenation of tryptophan and indole derivatives has been previously described. However, multiple cultivations and protein purification steps are necessary for their production. We present a bifunctional regeneration enzyme for two-step catalytic flavin regeneration using phosphite as an inexpensive sacrificial substrate. This fusion protein proved amenable to co-expression with various flavin-dependent Trp-halogenases and enables carrier-free immobilisation as combiCLEAs from a single cultivation for protein production and the preparative synthesis of halotryptophan. The scalability of this system was demonstrated by fed-batch fermentation in bench-top bioreactors on a 2.5 L scale. Furthermore, the inclusion of a 6-halotryptophan-specific dioxygenase into the co-expression strain further converts the halogenation product to the kynurenine derivative. This reaction cascade enables the one-pot synthesis of l-4-Cl-kynurenine and its brominated analogue on a preparative scale.

Performance of cross-linked enzyme crystals of engineered halohydrin dehalogenase HheG in different chemical reactor systems

Halohydrin dehalogenase HheG is an industrially interesting biocatalyst for the preparation of different β-substituted alcohols starting from bulky internal epoxides. We previously demonstrated that the immobilization of different HheG variants in the form of cross-linked enzyme crystals (CLECs) yielded stable and reusable enzyme immobilizes with increased resistance regarding temperature, pH, and the presence of organic solvents. Now, to further establish their preparative applicability, HheG D114C CLECs cross-linked with bis-maleimidoethane have been successfully produced on a larger scale using a stirred crystallization approach, and their application in different chemical reactor types (stirred tank reactor, fluidized bed reactor, and packed bed reactor) was systematically studied and compared for the ring opening of cyclohexene oxide with azide. This revealed the highest obtained space-time yield of 23.9 kgproduct  gCLEC -1  h-1  Lreactor volume -1 along with the highest achieved product enantiomeric excess [64%] for application in a packed-bed reactor. Additionally, lyophilization of those CLECs yielded a storage-stable HheG preparation that still retained 67% of initial activity (after lyophilization) after 6 months of storage at room temperature.

Insolubilization of Tramates versicolor laccase as cross-linked enzyme aggregates for the remediation of trace organic contaminants from municipal wastewater

The novelty of this study deals with the biocatalytic treatment of trace organic contaminants (TrOCs) from municipal wastewater by insolubilized laccase. Laccase from Trametes versicolor was aggregated by three-phase partitioning technique followed by cross-linking with glutaraldehyde to produce insolubilized laccase as cross-linked enzyme aggregates (CLEAs). The optimal conditions for CLEAs preparation include ammonium sulphate concentration of 83% (w/v), crude to t-butanol ratio of 1.00: 1.05 (v/v), pH 5.3, and glutaraldehyde concentration of 20 mM obtained via statistical design. The efficiency of insolubilization of the CLEAs laccase based on the k_cat/k_m ratio was approximately 4.8-fold greater than that of free laccase. The developed CLEAs showed greater resistance to product inhibition mediated by ABTS than the free enzyme and exhibited excellent catalytic activity even after the tenth successive cycle. Further, free laccase and the synthesized CLEAs laccase were utilized to treat five analgesics, two NSAIDS, three antibiotics, two antilipemics, and three pesticides in the municipal wastewater. Under the batch process with operating conditions of pH 7.0 and 20 °C, 1000 U/L of CLEAs, laccase removed 11 TrOCs in the range of about 20-99%. However, the inactivated CLEAs only adsorbed 2-25% of TrOCs. It was observed that acetaminophen, mefenamic acid, trimethoprim, and metolachlor depicted almost complete removal with CLEAs laccase. The performance of CLEAs laccase in a perfusion basket reactor was tested for the removal of TrOCs from municipal wastewater.

Optimization of cephalosporin C acylase immobilization using crosslinked enzyme aggregates technique

Cephalosporin C acylase (CCA) is an essential enzyme for the one-step conversion of cephalosporin C into 7-aminocephalosporanic acid (7-ACA), an intermediate compound used to synthesize various semi-synthetic cephalosporin antibiotics. The industrial process prefers to use enzymes in immobilized form rather than soluble. A crosslinked enzyme aggregate (CLEAs) is a potential matrix-less enzyme immobilization technique to produce stable immobilized enzymes with high activity and low production costs. This study aimed to optimize the CCA immobilization using the CLEAs technique with Chitosan as a co-aggregate. The CCA lysate was obtained from harvesting CCA fermentation broth using a mutant strain of Escherichia coli through cell separation and lysis steps. Partially purified CCA by ammonium sulfate addition was conducted to obtain an active fraction of 20-60% saturation, followed by co-aggregation with Chitosan to form physical CCA aggregates. The aggregates were then immobilized by a crosslinking technique using glutaraldehyde to form CLEAs-CCA. Optimization of the immobilization process was carried out by Response Surface Methodology in three steps, (i) screening of the influencing factors, (ii) determining the level of the significant factors, and (iii) optimizing the immobilization condition. The CLEAs-CCA activity was used as a response parameter. Under optimum conditions, CLEAs-CCA activity obtained was 85.91 Ug-1.

Production and Characterization of Cross-Linked Aggregates of Geobacillus thermoleovorans CCR11 Thermoalkaliphilic Recombinant Lipase

Immobilization of enzymes has many advantages for their application in biotechnological processes. In particular, the cross-linked enzyme aggregates (CLEAs) allow the production of solid biocatalysts with a high enzymatic loading and the advantage of obtaining derivatives with high stability at low cost. The purpose of this study was to produce cross-linked enzymatic aggregates (CLEAs) of LipMatCCR11, a 43 kDa recombinant solvent-tolerant thermoalkaliphilic lipase from Geobacillus thermoleovorans CCR11. LipMatCCR11-CLEAs were prepared using (NH4)2SO4 (40% w/v) as precipitant agent and glutaraldehyde (40 mM) as cross-linker, at pH 9, 20 °C. A U10(56) uniform design was used to optimize CLEA production, varying protein concentration, ammonium sulfate %, pH, glutaraldehyde concentration, temperature, and incubation time. The synthesized CLEAs were also analyzed using scanning electron microscopy (SEM) that showed individual particles of <1 µm grouped to form a superstructure. The cross-linked aggregates showed a maximum mass activity of 7750 U/g at 40 °C and pH 8 and retained more than 20% activity at 100 °C. Greater thermostability, resistance to alkaline conditions and the presence of organic solvents, and better durability during storage were observed for LipMatCCR11-CLEAs in comparison with the soluble enzyme. LipMatCCR11-CLEAs presented good reusability by conserving 40% of their initial activity after 9 cycles of reuse.

Design for preparation of more active cross-linked enzyme aggregates of Burkholderia cepacia lipase using palm fiber residue

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.

Dual miRNases for Triple Incision of miRNA Target: Design Concept and Catalytic Performance

Irreversible destruction of disease-associated regulatory RNA sequences offers exciting opportunities for safe and powerful therapeutic interventions against human pathophysiology. In 2017, for the first time we introduced miRNAses–miRNA-targeted conjugates of a catalytic peptide and oligonucleotide capable of cleaving an miRNA target. Herein, we report the development of Dual miRNases against oncogenic miR-21, miR-155, miR-17 and miR-18a, each containing the catalytic peptide placed in-between two short miRNA-targeted oligodeoxyribonucleotide recognition motifs. Substitution of adenines with 2-aminoadenines in the sequence of oligonucleotide “shoulders” of the Dual miRNase significantly enhanced the efficiency of hybridization with the miRNA target. It was shown that sequence-specific cleavage of the target by miRNase proceeded metal-independently at pH optimum 5.5–7.5 with an efficiency varying from 15% to 85%, depending on the miRNA sequence. A distinct advantage of the engineered nucleases is their ability to additionally recruit RNase H and cut miRNA at three different locations. Such cleavage proceeds at the central part by Dual miRNase, and at the 5′- and 3′-regions by RNase H, which significantly increases the efficiency of miRNA degradation. Due to increased activity at lowered pH Dual miRNases could provide an additional advantage in acidic tumor conditions and may be considered as efficient tumor-selective RNA-targeted therapeutic.

Cross-linked α-galactosidase aggregates: optimization, characterization and application in the hydrolysis of raffinose-type oligosaccharides in soymilk

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 (K_M , V_max and k_cat ) 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.

CLEAs, Combi-CLEAs and ‘Smart’ Magnetic CLEAs: Biocatalysis in a Bio-Based Economy

Biocatalysis has emerged in the last decade as a pre-eminent technology for enabling the envisaged transition to a more sustainable bio-based economy. For industrial viability it is essential that enzymes can be readily recovered and recycled by immobilization as solid, recyclable catalysts. One method to achieve this is via carrier-free immobilization as cross-linked enzyme aggregates (CLEAs). This methodology proved to be very effective with a broad selection of enzymes, in particular carbohydrate-converting enzymes. Methods for optimizing CLEA preparations by, for example, adding proteic feeders to promote cross-linking, and strategies for making the pores accessible for macromolecular substrates are critically reviewed and compared. Co-immobilization of two or more enzymes in combi-CLEAs enables the cost-effective use of multiple enzymes in biocatalytic cascade processes and the use of “smart” magnetic CLEAs to separate the immobilized enzyme from other solids has raised the CLEA technology to a new level of industrial and environmental relevance. Magnetic-CLEAs of polysaccharide-converting enzymes, for example, are eminently suitable for use in the conversion of first and second generation biomass.

Evaluation of Strategies to Produce Highly Porous Cross-Linked Aggregates of Porcine Pancreas Lipase with Magnetic Properties

The preparation of highly porous magnetic crosslinked aggregates (pm-CLEA) of porcine pancreas lipase (PPL) is reported. Some strategies to improve the volumetric activity of the immobilized biocatalyst were evaluated, such as treatment of PPL with enzyme surface-modifying agents (polyethyleneimine or dodecyl aldehyde), co-aggregation with protein co-feeders (bovine serum albumin and/or soy protein), use of silica magnetic nanoparticles functionalized with amino groups (SMNPs) as separation aid, and starch as pore-making agent. The combination of enzyme surface modification with dodecyl aldehyde, co-aggregation with SMNPs and soy protein, in the presence of 0.8% starch (followed by hydrolysis of the starch with α-amylase), yielded CLEAs expressing high activity (immobilization yield around 100% and recovered activity around 80%), high effectiveness factor (approximately 65% of the equivalent free enzyme activity) and high stability at 40 °C and pH 8.0, i.e., PPL CLEAs co-aggregated with SMNPs/bovine serum albumin or SMNPs/soy protein retained 80% and 50% activity after 10 h incubation, respectively, while free PPL was fully inactivated after 2 h. Besides, highly porous magnetic CLEAs co-aggregated with soy protein and magnetic nanoparticles (pm-SP-CLEAs) showed good performance and reusability in the hydrolysis of tributyrin for five 4h-batches.

Effectiveness of cross-linked enzyme aggregates of cellulolytic enzymes in hydrolyzing wheat straw

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.

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides.

Hybrid Cross-Linked Lipase Aggregates with Magnetic Nanoparticles: A Robust and Recyclable Biocatalysis for the Epoxidation of Oleic Acid

Highly stable and easily recyclable hybrid magnetic cross-linked lipase aggregates (HM-CSL-CLEAs) were prepared by coaggregation of lipase aggregates with nonfunctionalized magnetic nanoparticles and subsequent chemical cross-linking with glutaraldehyde. Analysis by SEM and CLSM indicated that the CLEAs were embedded in nanoparticle aggregates instead of covalently immobilized. The resulting HM-CSL-CLEAs exhibited higher thermostability, storage stability, and reusability than standard CLEAs. For example, HM-CSL-CLEAs maintained >60% of their initial activity after 40 min of incubation at 60 °C, whereas standard CLEAs lost most of their activities. The HM-CSL-CLEAs can be easily recovered from the reaction mixture by an external magnetic field. Moreover, the H2O2 tolerance of the lipase in HM-CSL-CLEAs was also enhanced, which could relieve the inhibitory effect on lipase activity. A high conversion yield (55%) for the epoxidation of oleic acid using H2O2 as oxidizing agent was achieved by HM-CSL-CLEAs.