Real-time dynamic adsorption processes of cytochrome c on an electrode observed through electrochemical high-speed atomic force microscopy

Intermolecular Electrostatic Interactions in Cytochrome c Protein Monolayer on Montmorillonite Alumosilicate Surface: A Positive Cooperative Effect

Montmorillonite (MM) crystal nanoplates acquire anticancer properties when coated with the mitochondrial protein cytochrome c (cytC) due to the cancer cells' capability to phagocytize cytC-MM colloid particles. The introduced exogenous cytC initiates apoptosis: an irreversible cascade of biochemical reactions leading to cell death. In the present research, we investigate the organization of the cytC layer on the MM surface by employing physicochemical and computer methods-microelectrophoresis, static, and electric light scattering-to study cytC adsorption on the MM surface, and protein electrostatics and docking to calculate the local electric potential and Gibbs free energy of interacting protein globules. The found protein concentration dependence of the adsorbed cytC quantity is nonlinear, manifesting a positive cooperative effect that emerges when the adsorbed cytC globules occupy more than one-third of the MM surface. Computer analysis reveals that the cooperative effect is caused by the formation of protein associates in which the cytC globules are oriented with oppositely charged surfaces. The formation of dimers and trimers is accompanied by a strong reduction in the electrostatic component of the Gibbs free energy of protein association, while the van der Waals component plays a secondary role.

Tripeptide Self-Assembled Monolayers as Biocompatible Surfaces for Cytochrome c Electrochemistry

Biocompatible tripeptide self-assembled monolayers (SAMs) are designed with a carboxylate group on the terminal amino acid (glutamate, aspartate, or amino adipate) to electrostatically attract the lysine groups around the heme crevice in horse heart cytochrome c (cyt c), creating an electroactive protein/tripeptide/Au interfacial structure. Exposing the peptide/Au electrode to cyt c resulted in an 11 ± 3 pmol/cm² electroactive protein surface coverage. Topographical images of the interfacial structure are obtained down to single-protein resolution by atomic force microscopy. Uniform protein monolayer assemblies are formed on the Au electrode with no major surface roughness changes. The cyt c/peptide/Au electrode systems were examined electrochemically to probe surface charge effects on the redox thermodynamics and kinetics of cyt c. Neutralization of protein surface charge due to adsorption on anionic COOH-terminated SAMs was found to change the formal potential, as determined by cyclic voltammetry. The cyt c/peptide/Au electrodes exhibit formal potentials shifted to more positive values, have a surface carboxylic acid pK_a of 6 or higher, and produce effective cyt c surface charges (Z_ox) of -6 to -14. The Marcus theory is utilized to determine the protein electron transfer rates, which are ∼5 times faster for cyt c/tripeptide/Au compared to cyt c/11-mercaptoundecanoic acid SAMs of similar chain lengths.

Sequence Programming with Dynamic Boronic Acid/Catechol Binary Codes

The development of a synthetic code that enables a sequence programmable feature like DNA represents a key aspect toward intelligent molecular systems. We developed herein the well-known dynamic covalent interaction between boronic acids (BAs) and catechols (CAs) into synthetic nucleobase analogs. Along a defined peptide backbone, BA or CA residues are arranged to enable sequence recognition to their complementary strand. Dynamic strand displacement and errors were elucidated thermodynamically to show that sequences are able to specifically select their partners. Unlike DNA, the pH dependency of BA/CA binding enables the dehybridization of complementary strands at pH 5.0. In addition, we demonstrate the sequence recognition at the macromolecular level by conjugating the cytochrome c protein to a complementary polyethylene glycol chain in a site-directed fashion.

Removal of Cr6+ ions from water by electrosorption on modified activated carbon fibre felt

Electrosorption is a novel desalination technique that has many advantages in the treatment of sewage. However, commercially available activated carbon electrodes for electrosorption commonly have low microporosity, poor moulding performance, and low adsorption and regeneration efficiency. Here, we evaluated a novel adsorbent material, activated carbon fibre felt (ACFF), for electrosorption of chromium ions (Cr⁶⁺) in sewage treatment. The ACFF was modified with 20% nitric acid and its modified structure was characterized. The modified ACFF was used as an adsorbing electrode to investigate its desalination effect by electrosorption. Results showed that compared with those of unmodified ACFF, the modified ACFF had more carbonyl and carboxyl groups and the specific surface area, average pore size and micropore volume of the modified ACFF also improved by 32.2%, 2.5% and 23.1%, respectively. The kinetics of Cr⁶⁺ adsorption conformed to the pseudo-second-order kinetic equation, and the adsorption isotherm conformed to the Langmuir model. In addition, the regeneration rate of the modified ACFF electrode was more than 94%. In conclusion, the modified ACFF exhibits excellent electrosorption and regeneration performance for Cr⁶⁺ removal from water and thus is of great value for promotion in sewage treatment.

Optimum Substrates for Imaging Biological Molecules with High-Speed Atomic Force Microscopy

Recent progresses in high-speed atomic force microscopy (HS-AFM) have enabled us to directly visualize dynamic processes of various proteins in liquid conditions. One of the key factors leading to successful HS-AFM observations is the selection of an appropriate substrate depending on molecules to be observed. For the HS-AFM imaging, a target molecule must be absorbed on a substrate by controlling its orientation without impairing the dynamics or physiological function of the molecule. In this chapter, we describe protocols for preparation of substrates that have been used for HS-AFM and then introduce observation examples on dynamic processes of biological molecules.

Tunable Semicrystalline Thin Film Cellulose Substrate for High-Resolution, In-Situ AFM Characterization of Enzymatic Cellulose Degradation

In the field of enzymatic cellulose degradation, fundamental interactions between different enzymes and polymorphic cellulose materials are of essential importance but still not understood in full detail. One technology with the potential of direct visualization of such bioprocesses is atomic force microscopy (AFM) due to its capability of real-time in situ investigations with spatial resolutions down to the molecular scale. To exploit the full capabilities of this technology and unravel fundamental enzyme-cellulose bioprocesses, appropriate cellulose substrates are decisive. In this study, we introduce a semicrystalline-thin-film-cellulose (SCFTC) substrate which fulfills the strong demands on such ideal cellulose substrates by means of (1) tunable polymorphism via variable contents of homogeneously sized cellulose nanocrystals embedded in an amorphous cellulose matrix; (2) nanoflat surface topology for high-resolution and high-speed AFM; and (3) fast, simple, and reproducible fabrication. The study starts with a detailed description of SCTFC preparation protocols including an in-depth material characterization. In the second part, we demonstrate the suitability of SCTFC substrates for enzymatic degradation studies by combined, individual, and sequential exposure to TrCel6A/TrCel7A cellulases (Trichoderma reesei) to visualize synergistic effects down to the nanoscale.