Production and covalent immobilisation of the recombinant bacterial carbonic anhydrase (SspCA) onto magnetic nanoparticles

Rational design engineering of a more thermostable Sulfurihydrogenibium yellowstonense carbonic anhydrase for potential application in carbon dioxide capture technologies

Implementing hyperthermostable carbonic anhydrases into CO2 capture and storage technologies in order to increase the rate of CO2 absorption from the industrial flue gases is of great importance from technical and economical points of view. The present study employed a combination of in silico tools to further improve thermostability of a known thermostable carbonic anhydrase from Sulfurihydrogenibium yellowstonense. Experimental results showed that our rationally engineered K100G mutant not only retained the overall structure and catalytic efficiency but also showed a 3 °C increase in the melting temperature and a two-fold improvement in the enzyme half-life at 85 °C. Based on the molecular dynamics simulation results, rearrangement of salt bridges and hydrogen interactions network causes a reduction in local flexibility of the K100G variant. In conclusion, our study demonstrated that thermostability can be improved through imposing local structural rigidity by engineering a single-point mutation on the surface of the enzyme.

Biomimetic Carbon Sequestration and Cyanate Detoxification Using Heat-Purified Carbonic Anhydrase from Sulfurihydrogenibium yellowstonense

The reaction condition for purifying carbonic anhydrase from Sulfurihydrogenibium yellowstonense (SspCA) by direct heating without prior cell lysis was optimized; heating at 70 °C for 5 min resulted in the highest total activity of 23,460 WAU (Wilbur-Anderson unit) from a 50 mL culture. Heat-purified SspCA was examined for its capability to increase the rate of the mineralization of CO2; compared with an uncatalyzed control, the onset time of CaCO3 formation was shortened by up to 71%. Cyanase can be used to degrade toxic cyanate; however, one of the limitations of this biomimetic process is that the reaction needs HCO3- as a substrate. Heat-purified SspCA was combined with heat-purified cyanase from Thermomyces lanuginosus to alleviate the HCO3- dependence; in industrial wastewater, the HCO3- required was reduced by 50% when 0.75 WAU of SspCA was added. Heat-purified SspCA is stable at 4 °C; 88% of the initial activity was retained for up to five weeks. Partially purified SspCA can be obtained with ease and applied to a variety of applications.

Microbial carbonic anhydrase mediated carbon capture, sequestration & utilization: A sustainable approach to delivering bio-renewables

In the recent scenario, anthropogenic interventions have alarmingly disrupted climatic conditions. The persistent change in the climate necessitates carbon neutrality. Efficient ways of carbon capture and sequestration could be employed for sustainable product generation. Carbonic anhydrase (CA) is an enzyme that reversibly catalyzes the conversion of carbon dioxide to bicarbonate ions, further utilized by cells for metabolic processes. Hence, utilizing CA from microbial sources for carbon sequestration and the corresponding delivery of bio-renewables could be the eco-friendly approach. Consequently, the microbial CA and amine-based carbon capture chemicals are synergistically applied to enhance carbon capture efficiency and eventual utilization. This review comprehends recent developments coupled with engineering techniques, especially in microbial CA, to create integrated systems for CO₂ sequestration. It envisages developing sustainable approaches towards mitigating environmental CO₂ from industries and fossil fuels to generate bio-renewables and other value-added chemicals.

Effective utilization of magnetic nano-coupled cloned β-xylanase in saccharification process

The β-xylanase gene (DCE06_04615) with 1041 bp cloned from Thermotoga naphthophila was expressed into E. coli BL21 DE3. The cloned β-xylanase was covalently bound to iron oxide magnetic nanoparticles coated with silica utilizing carbodiimide. The size of the immobilized MNPs (50 nm) and their binding with β-xylanase were characterized by Fourier-transform electron microscopy (FTIR) (a change in shift particularly from C–O to C–N) and transmission electron microscopy (TEM) (spherical in shape and 50 nm in diameter). The results showed that enzyme activity (4.5 ± 0.23 U per mL), thermo-stability (90 °C after 4 hours, residual activity of enzyme calculated as 29.89% ± 0.72), pH stability (91% ± 1.91 at pH 7), metal ion stability (57% ± 1.08 increase with Ca²⁺), reusability (13 times) and storage stability (96 days storage at 4 °C) of the immobilized β-xylanase was effective and superior. The immobilized β-xylanase exhibited maximal enzyme activity at pH 7 and 90 °C. Repeated enzyme assay and saccharification of pretreated rice straw showed that the MNP-enzyme complex exhibited 56% ± 0.76 and 11% ± 0.56 residual activity after 8 times and 13 times repeated usage. The MNP-enzyme complex showed 17.32% and 15.52% saccharification percentage after 1^st and 8^th time usage respectively. Immobilized β-xylanase exhibited 96% residual activity on 96 days' storage at 4 °C that showed excellent stability.

The β-xylanase gene (DCE06_04615) with 1041 bp cloned from Thermotoga naphthophila was expressed into E. coli BL21 DE3.

Enzymatic characteristics of immobilized carbonic anhydrase and its applications in CO2 conversion

Native carbonic anhydrase (CA) has been widely used in several different applications due to its catalytic function in the interconversion of carbon dioxide (CO₂) and carbonic acid. However, subject to its stability and recyclability, native CA often deactivates when in harsh environments, which restricts its applications in the commercial market. Maintaining the stability and high catalytic activity of CA is challenging. Immobilization provides an effective route that can improve enzymatic stability. Through the interaction of covalent bonds and van der Waals forces, water-soluble CA can be combined with various insoluble supports to form water-insoluble immobilized CA so that CA stability and utilization can be greatly improved. However, if the immobilization method or immobilization condition is not suitable, it often leads to a decrease in CA activity, reducing the application effects on CO₂ conversion. In this review, we discuss existing immobilization methods and applications of immobilized CA in the environmental field, such as the mineralization of carbon dioxide and multienzyme cascade catalysis based on CA. Additionally, prospects in current development are outlined. Because of the many outstanding and superior properties after immobilization, CA is likely to be used in a wide variety of scientific and technical areas in the future.

Effect of bicarbonate on growth of the oleaginous microalga Botryococcus braunii

The effect of bicarbonate, produced by the enzymatic hydration of CO2 from postcombustion fumes, was investigated on Botryococcus braunii growth. The NaHCO3, supplied to cultures in the role of inorganic carbon source is proposed as a more eco-sustainable alternative to gaseous CO2. The salt was provided to the cultures at the final concentration of 0.5-1.5-2.5 g L- 1. The growth rate was considered for specific time intervals (T0-T5, T5-T10 and T0- T10) showing values significantly higher in the culture supplemented with 2.5 g L-1 bicarbonate. The doubling times were also considered in all experimental cultures showing a faster doubling for the period T0÷T5. The increase in pH drives the increase in growth in the experimental conditions in which the salt was added. The results suggest that bicarbonate is able to promote the algal growth, therefore it can be considered a valid alternative to CO2 gas.

Thermostability enhancement of the α-carbonic anhydrase from Sulfurihydrogenibium yellowstonense by using the anchoring-and-self-labelling-protein-tag system (ASLtag)

Carbonic anhydrases (CAs, EC 4.2.1.1) are a superfamily of ubiquitous metalloenzymes present in all living organisms on the planet. They are classified into seven genetically distinct families and catalyse the hydration reaction of carbon dioxide to bicarbonate and protons, as well as the opposite reaction. CAs were proposed to be used for biotechnological applications, such as the post-combustion carbon capture processes. In this context, there is a great interest in searching CAs with robust chemical and physical properties. Here, we describe the enhancement of thermostability of the α-CA from Sulfurihydrogenibium yellowstonense (SspCA) by using the anchoring-and-self-labelling-protein-tag system (ASL^tag). The anchored chimeric H⁵-SspCA was active for the CO₂ hydration reaction and its thermostability increased when the cells were heated for a prolonged period at high temperatures (e.g. 70 °C). The ASL^tag can be considered as a useful method for enhancing the thermostability of a protein useful for biotechnological applications, which often need harsh operating conditions.

An AGT-based protein-tag system for the labelling and surface immobilization of enzymes on E. coli outer membrane

The use of natural systems, such as outer membrane protein A (OmpA), phosphoporin E (PhoE), ice nucleation protein (INP), etc., has been proved very useful for the surface exposure of proteins on the outer membrane of Gram-negative bacteria. These strategies have the clear advantage of unifying in a one-step the production, the purification and the in vivo immobilisation of proteins/biocatalysts onto a specific biological support. Here, we introduce the novel Anchoring-and-Self-Labelling-protein-tag (ASL^tag), which allows the in vivo immobilisation of enzymes on E. coli surface and the labelling of the neosynthesised proteins with the engineered alkylguanine-DNA-alkyl-transferase (H⁵) from Sulfolobus solfataricus. Our results demonstrated that this tag enhanced the overexpression of thermostable enzymes, such as the carbonic anhydrase (SspCA) from Sulfurihydrogenibium yellowstonense and the β-glycoside hydrolase (SsβGly) from S. solfataricus, without affecting their folding and catalytic activity, proposing a new tool for the improvement in the utilisation of biocatalysts of biotechnological interest.

Inhibition of Shiga toxin-converting bacteriophage development by novel antioxidant compounds

Oxidative stress may be the major cause of induction of Shiga toxin-converting (Stx) prophages from chromosomes of Shiga toxin-producing Escherichia coli (STEC) in human intestine. Thus, we aimed to test a series of novel antioxidant compounds for their activities against prophage induction, thus, preventing pathogenicity of STEC. Forty-six compounds (derivatives of carbazole, indazole, triazole, quinolone, ninhydrine, and indenoindole) were tested. Fifteen of them gave promising results and were further characterized. Eleven compounds had acceptable profiles in cytotoxicity tests with human HEK-293 and HDFa cell lines. Three of them (selected for molecular studies) prevent the prophage induction at the level of expression of specific phage genes. In bacterial cells treated with hydrogen peroxide, expression of genes involved in the oxidative stress response was significantly less efficient in the presence of the tested compounds. Therefore, they apparently reduce the oxidative stress, which prevents induction of Stx prophage in E. coli.

Activation Profile Analysis of CruCA4, an α-Carbonic Anhydrase Involved in Skeleton Formation of the Mediterranean Red Coral, Corallium rubrum

CruCA4, a coral α-carbonic anhydrase (CA, EC 4.2.1.1) involved in the biomineralization process of the Mediterranean red coral, Corallium rubrum, was investigated for its activation with a panel of amino acids and amines. Most compounds showed considerable activating properties, with a rather well defined structure-activity relationship. The most effective CruCA4 activators were d-His, 4-H₂N-l-Phe, Histamine, Dopamine, Serotonin, 1-(2-Aminoethyl)-piperazine, and l-Adrenaline, with activation constants in the range of 8-98 nM. Other amines and amino acids, such as d-DOPA, l-Tyr, 2-Pyridyl-methylamine, 2-(2-Aminoethyl) pyridine and 4-(2-Aminoethyl)-morpholine, were submicromolar CruCA4 activators, with K_A ranging between 0.15 and 0.93 µM. Since it has been shown that CA activators may facilitate the initial phases of in-bone mineralization, our study may be relevant for finding modulators of enzyme activity, which can enhance the formation of the red coral skeleton.

An Overview of the Bacterial Carbonic Anhydrases

Bacteria encode carbonic anhydrases (CAs, EC 4.2.1.1) belonging to three different genetic families, the α-, β-, and γ-classes. By equilibrating CO₂ and bicarbonate, these metalloenzymes interfere with pH regulation and other crucial physiological processes of these organisms. The detailed investigations of many such enzymes from pathogenic and non-pathogenic bacteria afford the opportunity to design both novel therapeutic agents, as well as biomimetic processes, for example, for CO₂ capture. Investigation of bacterial CA inhibitors and activators may be relevant for finding antibiotics with a new mechanism of action.

A one-step procedure for immobilising the thermostable carbonic anhydrase (SspCA) on the surface membrane of Escherichia coli

The carbonic anhydrase superfamily (CA, EC 4.2.1.1) of metalloenzymes is present in all three domains of life (Eubacteria, Archaea, and Eukarya), being an interesting example of convergent/divergent evolution, with its seven families (α-, β-, γ-, δ-, ζ-, η-, and θ-CAs) described so far. CAs catalyse the simple, but physiologically crucial reaction of carbon dioxide hydration to bicarbonate and protons. Recently, our groups characterised the α-CA from the thermophilic bacterium, Sulfurihydrogenibium yellowstonense finding a very high catalytic activity for the CO₂ hydration reaction (k_cat = 9.35 × 10⁵ s^-1 and k_cat/K_m = 1.1 × 10⁸ M^-1s^-1) which was maintained after heating the enzyme at 80 °C for 3 h. This highly thermostable SspCA was covalently immobilised within polyurethane foam and onto the surface of magnetic Fe₃O₄ nanoparticles. Here, we describe a one-step procedure for immobilising the thermostable SspCA directly on the surface membrane of Escherichia coli, using the INPN domain of Pseudomonas syringae. This strategy has clear advantages with respect to other methods, which require as the first step the production and the purification of the biocatalyst, and as the second step the immobilisation of the enzyme onto a specific support. Our results demonstrate that thermostable SspCA fused to the INPN domain of P. syringae ice nucleation protein (INP) was correctly expressed on the outer membrane of engineered E. coli cells, affording for an easy approach to design biotechnological applications for this highly effective thermostable catalyst.