Affinity induced immobilization of adenylate cyclase from the crude cell lysate for ATP conversion

Enhanced endogenous amino acids and energy metabolism level for cAMP biosynthesis by Arthrobacter sp. CCTCC 2013431 with citrate as cosubstrate

OBJECTIVES

In our previous study, citrate was used as auxiliary energy substance for improving cAMP fermentation performance, however, the regulation mechanism of citrate on improved cAMP contents was not clear. To elucidate the regulation mechanism, cAMP fermentations with/without citrate addition were conducted in a 7 L fermentor using Arthrobacter sp. CCTCC 2013431 and assays on key enzymes activities, energy metabolism level, amino acids contents and peroxidation level were performed.

RESULTS

With 3 g/L-broth sodium citrate added, cAMP concentration and conversion yield from glucose reached 4.34 g/L and 0.076 g/g which were improved by 30.7% and 29.8%, respectively, when compared with those of control. Citrate changed carbon flux distribution among different routes and more carbon flux was directed into pentose phosphate pathway beneficial to cAMP synthesis. Meanwhile, energy metabolism together with precursor amino acids levels were improved significantly owing to strengthened metabolic intensity of tricarboxylate cycle by exogenous citrate utilization which provided energy and substance basis for cAMP production. Moreover, higher glutamate synthesis and oxidative stress caused by citrate addition consumed excessive NADPH derived from pentose phosphate pathway by which feedback suppression for pentose phosphate pathway was relieved efficiently.

CONCLUSION

Citrate promoted cAMP fermentation production by Arthrobacter sp. CCTCC 2013431 due to enhanced precursor amino acids, energy metabolism level and relieved feedback suppression for pentose phosphate pathway.

Improved adenylate cyclase activity via affinity immobilization onto co-modified GO with bio-inspired adhesive and PEI

Adenylate cyclase (AC) can efficiently catalyze the conversion of adenosine triphosphate (ATP) to cyclic adenosine-3', 5'-monophosphate (cAMP). However, AC directly immobilized on substrate is not desirable due to enzyme inactivation. Herein, bio-inspired adhesive of polydopamine and polyethyleneimine (PDA/PEI) was used as flexible chains to graft on graphene oxide (GO), and the AC was directionally immobilized through affinity between metal ions and his-tags of AC. The properties of modified GO and the activity of immobilized AC were studied in detail. PDA/PEI layers have been proved to improve the amino density of GO surface for affinity groups decoration and adjust the interaction between AC and support. And modified GO by this novel method contributes to subsequent grafting and immobilization of AC by affinity. AC immobilized on modified GO exhibited high activity recovery with about 90 % of free AC, while enzyme immobilized on unmodified GO has been inactivated. This study offers a versatile approach for support modification and enzyme oriented immobilization. PDA/PEI functionalized GO can be used as a promising carrier to immobilize other his-tagged enzymes.

One-step selective affinity purification and immobilization of His-tagged enzyme by recyclable magnetic nanoparticles

The NiFe2O4 magnetic nanoparticles (NF-MNPs) were prepared for one-step selective affinity purification and immobilization of His-tagged recombinant glucose dehydrogenase (GluDH). The prepared nanoparticles were characterized by a Fourier-transform infrared spectrophotometer and microscopy. The immobilization and purification of His-tagged GluDH on NF-MNPs were investigated. The optimal immobilization conditions were obtained that mixed cell lysis and carriers in a ratio of 0.13 in pH 8.0 Tris-HCl buffer at 30℃ and incubated for 2 h. The highest activity recovery and protein bindings were 71.39% and 38.50 μg mg-1 support, respectively. The immobilized GluDH exhibited high thermostability, pH-stability and it can retain more than 65% of the initial enzyme after 10 cycles for the conversion of glucose to gluconolactone. Comparing with a commercial Ni-NTA resin, the NF-MNPs displayed a higher specific affinity with His-tagged recombinant GluDH.

Semi-Continuous Flow Biocatalysis with Affinity Co-Immobilized Ketoreductase and Glucose Dehydrogenase

The co-immobilization of ketoreductase (KRED) and glucose dehydrogenase (GDH) on highly cross-linked agarose (sepharose) was studied. Immobilization of these two enzymes was performed via affinity interaction between His-tagged enzymes (six histidine residues on the N-terminus of the protein) and agarose matrix charged with nickel (Ni²⁺ ions). Immobilized enzymes were applied in a semicontinuous flow reactor to convert the model substrate; α-hydroxy ketone. A series of biotransformation reactions with a substrate conversion of >95% were performed. Immobilization reduced the requirement for cofactor (NADP+) and allowed the use of higher substrate concentration in comparison with free enzymes. The immobilized system was also tested on bulky ketones and a significant enhancement in comparison with free enzymes was achieved.

Synthesis of magnetic nanoparticles with an IDA or TED modified surface for purification and immobilization of poly-histidine tagged proteins

Magnetic nanoparticles (MNPs) chelating with metal ions can specifically interact with poly-histidine peptides and facilitate immobilization and purification of proteins with poly-histidine tags. Fabrication of MNPs is generally complicated and time consuming. In this paper, we report the preparation of Ni(ii) ion chelated MNPs (Ni-MNPs) in two stages for protein immobilization and purification. In the first stage, organic ligands including pentadentate tris (carboxymethyl) ethylenediamine (TED) and tridentate iminodiacetic acid (IDA) and inorganic Fe₃O₄–SiO₂ MNPs were synthesized separately. In the next stage, ligands were grafted to the surface of MNPs and MNPs with a TED or IDA modified surface were acquired, followed by chelating with Ni(ii) ions. The Ni(ii) ion chelated forms of MNPs (Ni-MNPs) were characterized including morphology, surface charge, structure, size distribution and magnetic response. Taking a his-tagged glycoside hydrolase DspB (Dispersin B) as the protein representative, specific interactions were confirmed between DspB and Ni-MNPs. Purification of his-tagged DspB was achieved with Ni-MNPs that exhibited better performance in terms of purity and activity of DspB than commercial Ni-NTA. Ni-MNPs as enzyme carriers for DspB also exhibited good compatibility and reasonable reusability as well as improved performance in various conditions.

This article reports a novel approach for synthesizing magnetic nanoparticles with a modified surface for purification and immobilization of histidine-tagged proteins.

Fabrication of rigid and macroporous agarose microspheres by pre-cross-linking and surfactant micelles swelling method

A novel combined method of pre-cross-linking and surfactant micelles swelling was proposed in this study to fabricate highly cross-linked and macroporous agarose (HMA) microspheres. Agarose was chemically modified by allylglycidyl ether (AGE) as heterobifunctional cross-linker via its active glycidyl moieties before gel formation and pre-cross-linking was achieved. By this means, the effective concentration of cross-linker presented in agarose gel increased significantly, and thus cross-linking with a high-efficiency was achieved. Further to enhance the intraparticle mass transfer of agarose microspheres, the surfactant micelles swelling method was utilized to create interconnected macropores. Under the optimal condition, HMA microspheres with homogeneous reticular structure and pore size of hundreds nanometers were successfully prepared. They exhibited a low backpressure with a flow velocity as high as 1987 cm/h, which was much higher than that of commercial Sepharose 4 F F. HMA microspheres were then derivatized with carboxymethyl (CM) groups and applied in ion-exchange chromatography. As expected, CM-HMA column separated model proteins effectively even at a flow velocity three times higher than that of commercial CM-4 F F. Visualization of dynamic protein adsorption by confocal laser scanning microscope (CLSM) revealed that the intraparticle mass transfer of CM-HMA microspheres was intensified due to its macroporous structure. All of the results indicated the newly developed agarose microspheres were a promising medium for high-speed chromatography.

Biocatalytic Protein-Based Materials for Integration into Energy Devices

There is a current need to fabricate new biobased functional materials. Bottom-up approaches to assemble simple molecular units have shown promise for biomaterial fabrication due to their tunability and versatility for the incorporation of functionalities. Herein, the fabrication of catalytic protein thin films by the entrapment of catalase into protein films composed of a scaffolding protein is demonstrated. Extensive structural and functional characterization of the films provide evidence of the structural integrity, order, stability, catalytic activity, and reusability of the biocatalytic materials. Finally, these functional biomaterials are coupled with piezoelectric disks to fabricate a second generation of bio-inorganic generators. These devices are capable of producing electricity from renewable fuels through catalase-driven gas production that mechanically stimulates the piezoelectric material.

Immobilization of a polyphosphate kinase 2 by coordinative self-assembly of his-tagged units with metal-organic frameworks and its application in ATP regeneration from AMP

Self-assembly of the functional units onto the surface of nanoparticles is a powerful approach to generate functional nanosystems. In this work, we first expressed a recombinant class III polyphosphate kinase 2 (ArPPK2) with his-tag. It is able to synthesize ATP from AMP by a single enzyme, simplifying two-step reaction of ATP regeneration from AMP. Then we chose the Fe-based metal-organic frameworks (MOF)s as carriers to produce the enzyme-MOF biocomposite, based on the interaction between the his-tags and coordinatively unsaturated metal sites present on the external surface of MOFs by a self-assembly process. It was found that ArPPK2@MIL-101-NH₂@Fe₃O₄-COOH exhibited better reusability than other candidates during cycle analysis, preserving 70.1% of initial activity after reusing thirteen times, and also retained high storage stability. The optimum pH of the enzyme-MOF biocomposite was increased from 8.0 to 9.0 and the optimum temperature was increased from 30℃ to 45℃. Compared to free ArPPK2, the enzyme-MOF biocomposite showed increased thermal and pH stability. In addition, we successfully constructed an ATP regeneration system from AMP using the enzyme-MOF biocomposite, coupled with amide bond formation catalyzed by the adenylation domain of tyrocidine synthetase A (TycA-A). The immobilized ArPPK2 will provide a promising route for ATP regeneration from AMP in industrial processes. And the generation of the enzyme-MOF biocomposite by the self-assembly approach can be extended to efficiently immobilize other recombinant his-tagged enzymes.

Catalytic, thermodynamic and structural properties of an immobilized and highly thermostable alkaline protease from a haloalkaliphilic actinobacteria, Nocardiopsis alba TATA-5

A highly thermostable protease from a haloalkaliphilic actinobacteria was immobilized employing 5 different approaches on 24 carriers. On immobilization, the activation energy and deactivation rate constant decreased, which makes the immobilized protease favourable for applications. Similarly, pH and temperature stability was enhanced, while the V_max and K_m changed upon immobilization. The immobilized enzyme had greater stability in various metal ions and detergents. The structural topography of the immobilized enzyme elucidated by the FTIR suggested the function of aliphatic amines, alkenes and esters since amide I and II bands were affected. Noticeable decrease in the Amide A band suggests interaction between the immobilization carriers and -NH groups of the protease molecule. The suitability of the immobilized protease was established by designing a continuous flow enzyme bioreactor, displaying the enzyme half-life of 916.15 min at 60 °C. The enzyme reactor was highly efficient in the treatment of the municipal and dairy wastewater.