Specific and reversible immobilization of proteins tagged to the affinity polypeptide C-LytA on functionalized graphite electrodes

Enzymatic and Microbial Electrochemistry: Approaches and Methods

The coupling of enzymes and/or intact bacteria with electrodes has been vastly investigated due to the wide range of existing applications. These span from biomedical and biosensing to energy production purposes and bioelectrosynthesis, whether for theoretical research or pure applied industrial processes. Both enzymes and bacteria offer a potential biotechnological alternative to noble/rare metal-dependent catalytic processes. However, when developing these biohybrid electrochemical systems, it is of the utmost importance to investigate how the approaches utilized to couple biocatalysts and electrodes influence the resulting bioelectrocatalytic response. Accordingly, this tutorial review starts by recalling some basic principles and applications of bioelectrochemistry, presenting the electrode and/or biocatalyst modifications that facilitate the interaction between the biotic and abiotic components of bioelectrochemical systems. Focus is then directed toward the methods used to evaluate the effectiveness of enzyme/bacteria-electrode interaction and the insights that they provide. The basic concepts of electrochemical methods widely employed in enzymatic and microbial electrochemistry, such as amperometry and voltammetry, are initially presented to later focus on various complementary methods such as spectroelectrochemistry, fluorescence spectroscopy and microscopy, and surface analytical/characterization techniques such as quartz crystal microbalance and atomic force microscopy. The tutorial review is thus aimed at students and graduate students approaching the field of enzymatic and microbial electrochemistry, while also providing a critical and up-to-date reference for senior researchers working in the field.

Development of a Novel Cell Surface Attachment System to Display Multi-Protein Complex Using the Cohesin-Dockerin Binding Pair

Autodisplay of a multimeric protein complex on a cell surface is limited by intrinsic factors such as the types and orientations of anchor modules. Moreover, improper folding of proteins to be displayed often hinders functional cell surface display. While overcoming these drawbacks, we ultimately extended the applicability of the autodisplay platform to the display of a protein complex. We designed and constructed a cell surface attachment (CSA) system that uses a noncovalent protein-protein interaction. We employed the high-affinity interaction mediated by an orthogonal cohesin-dockerin (Coh-Doc) pair from Archaeoglobus fulgidus to build the CSA system. Then, we validated the orthogonal Coh-Doc binding by attaching a monomeric red fluorescent protein to the cell surface. In addition, we evaluated the functional anchoring of proteins fused with the Doc module to the autodisplayed Coh module on the surface of Escherichia coli. The designed CSA system was applied to create a functional attachment of dimeric α-neoagarobiose hydrolase to the surface of E. coli cells.

CLytA-DAAO, Free and Immobilized in Magnetic Nanoparticles, induces Cell Death in Human Cancer Cells

D-amino acid oxidase (DAAO) catalyzes the oxidation of D-amino acids generating hydrogen peroxide, a potential producer of reactive oxygen species. In this study, we used a CLytA-DAAO chimera, both free and bound to magnetic nanoparticles, against colon carcinoma, pancreatic adenocarcinoma, and glioblastoma cell lines. We found that the enzyme induces cell death in most of the cell lines tested and its efficiency increases significantly when it is immobilized in nanoparticles. We also tested this enzyme therapy in non-tumor cells, and we found that there is not cell death induction, or it is significantly lower than in tumor cells. The mechanism triggering cell death is apparently a classical apoptosis pathway in the glioblastoma cell lines, while in colon and pancreatic carcinoma cell lines, CLytA-DAAO-induced cell death is a necrosis. Our results constitute a proof of concept that an enzymatic therapy, based on magnetic nanoparticles-delivering CLytA-DAAO, could constitute a useful therapy against cancer and besides it could be used as an enhancer of other treatments such as epigenetic therapy, radiotherapy, and treatments based on DNA repair.

Electrodeposition of 4-Benzenesulfonic Acid onto a Graphite-Epoxy Composite Electrode for the Enhanced Voltammetric Determination of Caffeine in Beverages

Caffeine is widely present in food and drinks, such as teas and coffees, being also part of some currently commercialized medicines, but despite its enhancement on several functions of human body, its exceeding use can promote many health problems. In order to develop new fast approaches for the caffeine sensing, graphite-epoxy composite electrodes (GECE) were used as substrate, being modified by different diazonium salts, synthetized as their tetraflouroborate salts. An analytical method for caffeine quantification was developed, using sware wave voltammetry (SWV) in Britton-Robinson buffer pH 2.0. Detection limits for bare electrode and 4-benzenesulfonic modified electrode were observed circa 145 µmol·L^-1 and 1.3 µmol·L^-1, respectively. The results have shown that the modification shifts the oxidation peaks to lower potential. Kinetics of the reaction limited by diffusion was more expressive when caffeine was added to the solution, resulting in decreases of impedance, characterized by lower R _ct. All results for caffeine determination were compared to a reference chromatographic procedure (HPLC), showing no statistical difference. Analytical parameters for validation were suitably determined according to local legislation, leading to a linear behaviour from 5 to 150 µmol·L^-1; precision of 4.09% was evaluated based on the RDC 166/17, and accuracy was evaluated in comparison with the reference method, with recovery of 98.37 ± 2.58%.

Engineered (Lys)6-Tagged Recombinant Sulfide-Reactive Hemoglobin I for Covalent Immobilization at Multiwalled Carbon Nanotubes

The recombinant HbI was fused with a poly-Lys tag ((Lys)₆-tagged rHbI) for specific-site covalent immobilization on two carbon nanotube transducer surfaces, i.e., powder and vertically aligned carbon nanotubes. The immobilization was achieved by following two steps: (1) generation of amine-reactive ester from the carboxylic acid groups of the surfaces and (2) coupling these groups with the amine groups of the Lys-tag. We analyzed the immobilization process using different conditions and techniques to differentiate protein covalent attachment from physical adsorption. Fourier transform infrared microspectroscopy data showed a 14 cm^-1 displacement of the protein's amide I and amide II peaks to lower the frequency after immobilization. This result indicates a covalent attachment of the protein to the surface. Differences in the morphology of the carbon substrate with and without (Lys)₆-tagged rHbI confirmed protein immobilization, as observed by transmission electron microscopy. The electrochemical studies, which were performed to evaluate the redox center of the immobilized protein, show a confinement suitable for an efficient electron transfer system. More importantly, the electrochemical studies allowed determination of a redox potential for the new (Lys)₆-tagged rHbI. The data show that the protein is electrochemically active and retains its biological activity toward H₂S.

Molecular Cloning and Characterization of a (Lys)6-Tagged Sulfide-Reactive Hemoglobin I from Lucina pectinata

A poly-Lys tag was fused to the Lucina pectinata hemoglobin I (HbI) coding sequence and purified using an efficient and fast process. HbI is a hemeprotein that binds hydrogen sulfide (H2S) with high affinity and it has been used to understand physiologically relevant reactions of this signaling molecule. The (Lys)6-tagged rHbI construct was expressed in E. coli and purified by immobilization on a cation exchange matrix, followed by size-exclusion chromatography. The identity, structure, and function of the (Lys)6-tagged rHbI were assessed by mass spectrometry, small and wide X-ray scattering, optical spectroscopy, and kinetic analysis. The scattering and spectroscopic results showed that the (Lys)6-tagged rHbI is structurally and functionally analogous to the native protein as well as to the (His)6-tagged rHbI. Kinetics studies with H2S indicated that the association (k on) and dissociation (k off) rate constants were 1.4 × 10(5)/M/s and 0.1 × 10(-3)/s, respectively. This results confirmed that the (Lys)6-tagged rHbI binds H2S with the same high affinity as its homologue.