Carbonic Anhydrase Mimic Research Articles

Activity-enhanced Cu@ZIF-8/Ag carbonic anhydrase mimic for CO2 hydration and conversion

Carbonic anhydrase (CA) is an enzyme with unrivaled catalytic activity for CO2 hydration reactions. However, its high cost and poor stability have severely limited its industrial application in CO2 uptake. Constructing CA mimics is a promising strategy to overcome these limitations. In this work, a novel ZIF-8-based CA mimic, Cu@ZIF-8/Ag, was fabricated for CO2 capture and storage. Esterase experiments confirmed that Cu@ZIF-8/Ag had higher CA-mimicking activity than ZIF-8 and Cu@ZIF-8, indicating that Cu-doping and in-situ growth of Ag nanoparticles significantly increased CA-like activity. Simulating the mineralization process in industrial applications, Cu@ZIF-8/Ag yielded the highest CaCO3 yields. Additionally, Cu@ZIF-8/Ag has good reusability, with catalytic activity over 10 % higher than ZIF-8 even after seven adsorption and regeneration cycles. This activity-enhanced Cu@ZIF-8/Ag carbonic anhydrase mimic shows great potential for future CO2 capture.

Insights into Amorphous Metal‐Organic Framework as Carbonic Anhydrase Mimic

AbstractCarbonic anhydrase (CA) is an important enzyme which breaks the C−O bond and catalyzes the hydration of CO2 and developing artificial enzyme to mimic the function of CA is important for the related applications. Zeolitic imidazolate frameworks (ZIFs) with typical tetrahedral Zn−N coordination units which were similar to the catalytically active site of natural CA have been reported to displayed CA‐like activities. However, the activity of crystalline ZIFs remains unsatisfactory. Herein, amorphous zeolitic imidazolate framework (aZIF) was fabricated through a facile self‐assembly process and exhibited 2.2‐fold higher CA‐like hydrolytic activity than the corresponding crystalline ZIF‐8.This phenomenon can be ascribed to the unsaturated Zn−N coordination structure and mesopores inside aZIF. This work affords a new avenue for the rational design of nanozymes.

Synthetic hydrogel polymer nanoparticles as a structural mimic of carbonic anhydrase

Synthetic hydrogel polymer nanoparticles as a structural mimic of carbonic anhydrase

Polyethylenimine‐Grafted Silica Nanoparticles Facilitate Enzymatic Carbon Dioxide Conversion

AbstractPolyethylenimine (PEI)‐grafted silica nanoparticles were fabricated and characterized for the electrostatic immobilization of a CO2 conversion enzyme. PEI was supposed to serve as a carbonic anhydrase mimic for CO2 capture and conversion to HCO3− (the optimal substrate of many CO2 conversion enzymes) and was proved to assist phosphoenolpyruvate carboxylase to form a dual‐enzyme cascade system for CO2 conversion. The immobilized enzyme not only presented better thermostability, pH tolerance, and storage stability, but also enhanced the specific activity (three‐ and fourfold for HCO3− and CO2 as the substrates, respectively), with good reusability and low cost. It was proven that PEI‐grafted nanoparticles are highly efficient nanocarriers for immobilizing CO2‐converting enzymes in industrial applications.

Carbonic anhydrase mimics with rationally designed active sites for fine-tuned catalytic activity and selectivity in ester hydrolysis.

Numerous hydrolytic enzymes utilize zinc as a cofactor for catalysis. We here report water-soluble polymeric nanoparticles with zinc ions in active sites and a nearby base as a mimic of carbonic anhydrase (CA). Their pKa of 6.3-6.4 for zinc-bound water is lower than the 6.8-7.3 value for natural enzymes, which allows the catalyst to hydrolyze nonactivated alkyl esters under neutral conditions-a long sought-after goal for artificial esterases. The size and shape of the active site can be rationally tuned through a template used in molecular imprinting. Subtle structural changes in the template, including shifting an ethyl group by one C-N bond and removal of a methylene group, correlate directly with catalytic activity. A catalyst can be made to be highly specific or have broad substrate specificity through modular synthesis of templates.

Zinc-based deep eutectic solvent – An efficient carbonic anhydrase mimic for CO2 hydration and conversion

Carbonic anhydrase (CA) has demonstrated great potential to mitigate CO2 emissions by enzymatic conversion of CO2, while its commercial implementation is limited by the inherent shortcomings of CA, such as thermal and chemical instability, high sensitivity to the environment, and high cost. To overcome the drawbacks of CA and develop advanced technologies for mitigating CO2 emission, for the first time, mimetic CA (ZnHisGly) with the characteristics of natural CA was designed and synthesized, i.e., zinc-based deep eutectic solvent (DES), to boost CO2 hydration and conversion. The mimetic CA exhibited facile synthesis, high stability, and low cost as the characteristics of DES, and showed better catalytic performance compared to the currently reported mimetic CA. Particularly, its catalytic performance increased greatly with increasing pH and temperatures, which provides promising prospects in the industrial applications of DES-based CA mimics.

Protein-caged zinc porphyrin as a carbonic anhydrase mimic for carbon dioxide capture

Zinc tetraphenylporphyrin (Zn-TPP) solubilized by GroEL protein cage was prepared as a supramolecular mimic of carbonic anhydrase (CA) for CO2 capture. It is shown that the soluble Zn-TPP-GroEL complex can be formed easily by detergent dialysis. The Zn-TPP/GroEL binding ratio was found to increase with their dialysis ratio until reaching the maximum of about 30 porphyrins per protein cage. Moreover, the complex showed hydrase activity that catalyzes the CO2 hydration in HCO3− and H+. It is further seen that the catalytic activity of Zn-TPP-GroEL was about one-half of that of a bovine CA at 25 °C. On the other hand, as the temperature was increased to 60 °C close to an industrial CO2 absorption temperature, the natural enzyme lost function while Zn-TPP-GroEL exhibited better catalytic performance indicative of a higher thermal stability. Finally, we demonstrate that the GroEL-solubilized Zn-TPP is able to accelerate the precipitation of CO2 in the form of CaCO3 and has better long-term performance than the bovine CA. Thus a new type of nano-caged system mimicking natural CAs for potential applications in carbon capture has been established.

Reversible photoresponsive activity of a carbonic anhydrase mimic.

The carbonic anhydrase (CA) enzyme reversibly transforms carbon dioxide and water to a carbonate ion and a proton. Photoresponsive enzyme mimics, where the CA-activity can be turned on and off reversibly with light, have not been reported so far. We have designed an active site mimic that offers reversible control of the catalytic activity using light. Moreover, in the presence of a cationic polymer, we have demonstrated that the CA-activity was further enhanced by stabilizing the transition state with the cis-form of the enzyme mimic which can catalyze the hydration of gaseous CO2.

Metalloenzyme Mimicry at the Nodes of Metal-Organic Frameworks

In this issue of Chem, Dincă and co-workers show that the node of the metal-organic framework MFU-4l can be modified by anion exchange to serve as a biomimetic model of carbonic anhydrase given the similarity in their ligand fields. The resulting material, which has reactivity characteristics of the enzyme, gives great promise for CO2-related applications.

Enhanced CO2 absorption and desorption in a tertiary amine medium with a carbonic anhydrase mimic

We report the effects of a series of carbonic anhydrase (CA) model complexes on CO2 absorption and desorption in an aqueous tertiary amine medium. The CO2 hydration efficiency was determined under basic conditions by using stopped-flow kinetics experiments. Catalyst 6 was found to exhibit the best CO2 hydration efficiency (3.130 × 103 M−1 s−1) in the tertiary amine medium. In a highly concentrated tertiary amine medium, catalyst 2 was found to enhance the absorption and regeneration efficiency of CO2 by 10% and 24%, respectively. Our results for simple CA model complexes indicate that possible usage of synthesized complexes in post-combustion process.

Design of a zinc-finger hydrolase with a synthetic αββ protein.

Recent advances in protein design have opened avenues for the creation of artificial enzymes needed for biotechnological and pharmaceutical applications. However, designing efficient enzymes remains an unrealized ambition, as the design must incorporate a catalytic apparatus specific for the desired reaction. Here we present a de novo design approach to evolve a minimal carbonic anhydrase mimic. We followed a step-by-step design of first folding the main chain followed by sequence variation for substrate binding and catalysis. To optimize the fold, we designed an αββ protein based on a Zn-finger. We then inverse-designed the sequences to provide stability to the fold along with flexibility of linker regions to optimize Zn binding and substrate hydrolysis. The resultant peptides were synthesized and assessed for Zn and substrate binding affinity by fluorescence and ITC followed by evaluation of catalytic efficiency with UV-based enzyme kinetic assays. We were successful in mimicking carbonic anhydrase activity in a peptide of twenty two residues, using p-nitrophenyl acetate as a CO2 surrogate. Although our design had modest activity, being a simple structure is an advantage for further improvement in efficiency. Our approach opens a way forward to evolving an efficient biocatalyst for any industrial reaction of interest.

Improving carbon capture from power plant emissions with zinc- and cobalt-based catalysts

A carbonic anhydrase mimic converting CO2 to carbonic acid, deprotonated under highly basic conditions, and being converted to a carbamate upon reaction with monoethanolamine, a solvent reported for carbon capture reactions.

Evaluation of a Carbonic Anhydrase Mimic for Industrial Carbon Capture

Zinc(II) cyclen, a small molecule mimic of the enzyme carbonic anhydrase, was evaluated under rigorous conditions resembling those in an industrial carbon capture process: high pH (>12), nearly saturated salt concentrations (45% K2CO3) and elevated temperatures (100-130 °C). We found that the catalytic activity of zinc cyclen increased with increasing temperature and pH and was retained after exposure to a 45% w/w K2CO3 solution at 130 °C for 6 days. However, high bicarbonate concentrations markedly reduced the activity of the catalyst. Our results establish a benchmark level of stability and provide qualitative insights for the design of improved small-molecule carbon capture catalysts.

Signaling Pathways of ESE-16, an Antimitotic and Anticarbonic Anhydrase Estradiol Analog, in Breast Cancer Cells

The aim of this study was to characterize the in vitro action of 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) on non-tumorigenic MCF-12A, tumorigenic MCF-7 and metastatic MDA-MB-231 breast cancer cells. ESE-16 is able to inhibit the activity of a carbonic anhydrase II and a mimic of carbonic anhydrase IX in the nanomolar range. Gene and protein expression studies using various techniques including gene and antibody microarrays and various flow cytometry assays yielded valuable information about the mechanism of action of ESE-16. The JNK pathway was identified as an important pathway mediating the effects of ESE-16 while the p38 stress-induced pathway is more important in MDA-MB-231 cells exposed to ESE-16. Lysosomal rupture and iron metabolism was identified as important mediators of mitochondrial membrane depolarization. Abrogation of Bcl-2 phosphorylation status as a result of ESE-16 also plays a role in inducing mitochondrial membrane depolarization. The study provides a basis for future research projects to develop the newly synthesized compound into a clinically usable anticancer agent either alone or in combination with other agents.Keywords: Antimitotic, anticarbonic anhydrase IX, apoptosis, autophagy, cell cycle arrest, Bcl-2, JNK, p38, mitochondrial membrane depolarization, flow cytometry, gene expression and protein microarray, anticancer.

In Vitro Evaluation of ESE-15-ol, an Estradiol Analogue with Nanomolar Antimitotic and Carbonic Anhydrase Inhibitory Activity

Antimitotic compounds are still one of the most widely used chemotherapeutic anticancer drugs in the clinic today. Given their effectiveness against cancer it is beneficial to continue enhancing these drugs. One way is to improve the bioavailability and efficacy by synthesizing derivatives that reversibly bind to carbonic anhydrase II (CAII) in red blood cells followed by a slow release into the blood circulation system. In the present study we describe the in vitro biological activity of a reduced derivative of 2-ethyl-3-O-sulphamoyl-estradiol (2EE), 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol). ESE-15-ol is capable of inhibiting carbonic anhydrase activity in the nanomolar range and is selective towards a mimic of carbonic anhydrase IX when compared to the CAII isoform. Docking studies using Autodock Vina suggest that the dehydration of the D-ring plays a role towards the selectivity of ESE-15-ol to CAIX and that the binding mode of ESE-15-ol is substantially different when compared to 2EE. ESE-15-ol is able to reduce cell growth to 50% after 48 h at 50–75 nM in MCF-7, MDA-MB-231, and MCF-12A cells. The compound is the least potent against the non-tumorigenic MCF-12A cells. In vitro mechanistic studies demonstrate that the newly synthesized compound induces mitochondrial membrane depolarization, abrogates the phosphorylation status of Bcl-2 and affects gene expression of genes associated with cell death and mitosis.

Hydrolytic catalysis and structural stabilization in a designed metalloprotein

Metal ions are an important part of many natural proteins, providing structural, catalytic and electron transfer functions. Reproducing these functions in a designed protein is the ultimate challenge to our understanding of them. Here, we present an artificial metallohydrolase, which has been shown by X-ray crystallography to contain two different metal ions – a Zn(II) ion which is important for catalytic activity and a Hg(II) ion which provides structural stability. This metallohydrolase displays catalytic activity that compares well with several characteristic reactions of natural enzymes. It catalyses p-nitrophenyl acetate hydrolysis (pNPA) to within ~100-fold of the efficiency of human carbonic anhydrase (CA)II and is at least 550-fold better than comparable synthetic complexes. Similarly, CO2 hydration occurs with an efficiency within ~500-fold of CAII. While histidine residues in the absence of Zn(II) exhibit pNPA hydrolysis, miniscule apopeptide activity is observed for CO2 hydration. The kinetic and structural analysis of this first de novo designed hydrolytic metalloenzyme uncovers necessary design features for future metalloenzymes containing one or more metals.

Control of calcium carbonate polymorphism and morphology through biomimetic mineralization by means of nanotechnology.

In vitro biomimetic mineralization by means of nanotechnology allows the formation of calcium carbonate polymorphs at low temperatures (<25 degrees C) under a CO(2) atmosphere of 500-1500 ppm. A two-dimensional zinc-ion ordered array (zinc array), which acts as an active-site mimic of carbonic anhydrase, has been prepared by immersing the self-organized monolayer of 3-(2-imidazolin-1-y)propyltriethosilane on mica (ImSi substrate) into aqueous zinc solution. The zinc array mounted on the ImSi substrate catalyzed the conversion from CO(2) to HCO(3) (-), and accelerated the formation of calcium carbonate. In situ X-ray diffraction data of the formed calcium carbonate on the poly(L-aspartate)-coated chitin substrate (pAsp substrate), with calcium ion-recognition sites, demonstrated that the interaction between the zinc array and pAsp substrates formed both vaterite and calcite at low temperature (15 degrees C) and mainly vaterite at 25 degrees C; this interaction also controlled the morphology of calcium carbonate formed on pAsp substrate.