Molecular features of interaction involving hen egg white lysozyme immobilized on graphene oxide and the effect on activity

Enantioselective effects of chiral prothioconazole and its metabolites: Oxidative stress in HepG2 cells and lysozyme activity

Chiral pesticides may exhibit enantioselectivity in terms of bioconcentration, environmental fate, and reproductive toxicity. Here, chiral prothioconazole and its metabolites were selected to thoroughly investigate their enantioselective toxicity and mechanisms at the molecular and cellular levels. Multispectral techniques revealed that the interaction between chiral PTC/PTCD and lysozyme resulted in the formation of a complex, leading to a change in the conformation of lysozyme. Meanwhile, the effect of different conformations of PTC/PTCD on the conformation of lysozyme differed, and its metabolites were able to exert a greater effect on lysozyme compared to prothioconazole. Moreover, the S-configuration of PTCD interacted most strongly with lysozyme. This conclusion was further verified by DFT calculations and molecular docking as well. Furthermore, the oxidative stress indicators within HepG2 cells were also affected by chiral prothioconazole and its metabolites. Specifically, S-PTCD induced more substantial perturbation of the normal oxidative stress processes in HepG2 cells, and the magnitude of the perturbation varied significantly among different configurations (P > 0.05). Overall, chiral prothioconazole and its metabolites exhibit enantioselective effects on lysozyme conformation and oxidative stress processes in HepG2 cells. This work provides a scientific basis for a more comprehensive risk assessment of the environmental behaviors and effects caused by chiral pesticides, as well as for the screening of highly efficient and less biotoxic enantiomeric monomers.

Enzyme immobilization studied through molecular dynamic simulations

In recent years, simulations have been used to great advantage to understand the structural and dynamic aspects of distinct enzyme immobilization strategies, as experimental techniques have limitations in establishing their impact at the molecular level. In this review, we discuss how molecular dynamic simulations have been employed to characterize the surface phenomenon in the enzyme immobilization procedure, in an attempt to decipher its impact on the enzyme features, such as activity and stability. In particular, computational studies on the immobilization of enzymes using i) nanoparticles, ii) self-assembled monolayers, iii) graphene and carbon nanotubes, and iv) other surfaces are covered. Importantly, this thorough literature survey reveals that, while simulations have been primarily performed to rationalize the molecular aspects of the immobilization event, their use to predict adequate protocols that can control its impact on the enzyme properties is, up to date, mostly missing.

Stabilization of lysozyme in aqueous dispersion of graphene oxide sheets

This study examines the effect of surface oxygen groups upon ability of graphene oxide (GO) sheets in suppressing the fibrillation of lysozyme (LYZ). Graphite was oxidized using 6 and 8 wt equivalents of KMnO₄, and as produced sheets were abbreviated as GO-06 and GO-08, respectively. Particulate characteristics of sheets were characterized by light scattering and electron microscopic techniques, and their interaction with LYZ was analysed by circular dichroism (CD) spectroscopy. After ascertaining acid-driven conversion of LYZ to fibrillary form, we have shown that the fibrillation of dispersed protein can be prevented by adding GO sheets. Inhibitory effect could be attributed to binding of LYZ over the sheets via noncovalent forces. A comparison between GO-06 and GO-08 samples showed superior binding affinity of the latter. Higher aqueous dispersibility and density of oxygenated groups in GO-08 sheets would have facilitated the adsorption of protein molecules, thus making them unavailable for aggregation. Pre-treatment of GO sheets with Pluronic 103 (P103, a nonionic triblock copolymer), caused reduction in the adsorption of LYZ. P103 aggregates would have rendered the sheet surface unavailable for the adsorption of LYZ. Based on these observations, we conclude that fibrillation of LYZ can be prevented in association with graphene oxide sheets.

Graphene Oxide–Protein-Based Scaffolds for Tissue Engineering. Recent Advances and Applications

The field of tissue engineering is constantly evolving as it aims to develop bioengineered and functional tissues and organs for repair or replacement. Due to their large surface area and ability to interact with proteins and peptides, graphene oxides offer valuable physiochemical and biological features for biomedical applications and have been successfully employed for optimizing scaffold architectures for a wide range of organs, from the skin to cardiac tissue. This review critically focuses on opportunities to employ protein–graphene oxide structures either as nanocomposites or as biocomplexes and highlights the effects of carbonaceous nanostructures on protein conformation and structural stability for applications in tissue engineering and regenerative medicine. Herein, recent applications and the biological activity of nanocomposite bioconjugates are analyzed with respect to cell viability and proliferation, along with the ability of these constructs to sustain the formation of new and functional tissue. Novel strategies and approaches based on stem cell therapy, as well as the involvement of the extracellular matrix in the design of smart nanoplatforms, are discussed.

Inhibition of microtubule assembly and cytotoxic effect of graphene oxide on human colorectal carcinoma cell HCT116

Nanomaterials, such as graphene oxide (GO), are increasingly being investigated for their suitability in biomedical applications. Tubulin is the key molecule for the formation of microtubules crucial for cellular function and proliferation, and as such an appealing target for developing anticancer drug. Here we employ biophysical techniques to study the effect of GO on tubulin structure and how the changes affect the tubulin/microtubule assembly. GO disrupts the structural integrity of the protein, with consequent retardation of tubulin polymerization. Investigating the anticancer potential of GO, we found that it is more toxic to human colon cancer cells (HCT116), as compared to human embryonic kidney epithelial cells (HEK293). Immunocytochemistry indicated the disruption of microtubule assembly in HCT116 cells. GO arrested cells in the S phase with increased accumulation in Sub-G1 population of cell cycle, inducing apoptosis by generating reactive oxygen species (ROS) in a dose- and time-dependent manner. GO inhibited microtubule formation by intervening into the polymerization of tubulin heterodimers both in vitro and ex vivo, resulting in growth arrest at the S phase and ROS induced apoptosis of HCT116 colorectal carcinoma cells. There was no significant harm to the HEK293 kidney epithelial cells used as control. Our report of pristine GO causing ROS-induced apoptosis of cancer cells and inhibition of tubulin-microtubule assembly can be of interest in cancer therapeutics and nanomedicine.

Evaluation of Utilizing Functionalized Graphene Oxide Nanoribbons as Compatible Biomaterial for Lysozyme

Graphene oxide nanoribbons with superior physicochemical properties acquired from graphene and carbon nanotubes have been used in various applications including biomedical applications. For biomedical applications, it is of utmost importance to understand how these graphene oxide nanoribbons interact with proteins and the influence they have on protein conformation and function. In this regard, an attempt has been made to evaluate the utility of graphene oxide nanoribbons as a compatible biomaterial for lysozyme (Lys) protein. In this study, graphene oxide nanoribbons (GONRs) synthesized from multiwalled carbon nanotubes (MWCNTs) were first functionalized with (3-aminopropyl)triethoxysilane (APTES) and further modified with vanillin (Val) to obtain Val-APTES-GONRs. On characterization, it was found that the Val-APTES-GONRs material had a ribbonlike morphology with abundant functionalities for interaction with protein. On evaluation of Val-APTES-GONRs as a compatible biomaterial for Lys, studies revealed that a lower concentration of the as-synthesized material has less influence on the conformation and the structure of Lys with better activity, whereas higher concentrations of the as-synthesized material had a greater influence on conformation and the structure of Lys with decreased activity. Overall, the thermal stability of Lys was maintained after introducing the Val-APTES-GONRs material. In addition, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and Raman spectroscopies were performed for Lys composites with Val-APTES-GONRs for further understanding biomolecular interactions. This study is beneficial for designing advanced graphene-based materials for numerous bioinspired applications and better biomaterials for biotechnological use.

Effect of gold nanoparticles on the structure and neuroprotective function of protein L-isoaspartyl methyltransferase (PIMT)

Fibrillation of peptides and proteins is implicated in various neurodegenerative diseases and is a global concern. Aging leads to the formation of abnormal isoaspartate (isoAsp) residues from isomerization of normal aspartates in proteins, triggering fibril formation that leads to neurodegenerative diseases. Protein L-isoaspartyl methyltransferase (PIMT) is a repair enzyme which recognizes and converts altered isoAsp residues back to normal aspartate. Here we report the effect of gold nanoparticles (AuNPs) of different sizes on the structure and function of PIMT. Spherical AuNPs, viz. AuNS5, AuNS50 and AuNS100 (the number indicating the diameter in nm) stabilize PIMT, with AuNS100 exhibiting the best efficacy, as evident from various biophysical experiments. Isothermal titration calorimetry (ITC) revealed endothermic, but entropy driven mode of binding of PIMT with all the three AuNSs. Methyltransferase activity assay showed enhanced activity of PIMT in presence of all AuNSs, the maximum being with AuNS100. The efficacy of PIMT in presence of AuNS100 was further demonstrated by the reduction of fibrillation of Aβ42, the peptide that is implicated in Alzheimer's disease. The enhancement of anti-fibrillation activity of PIMT with AuNS100 was confirmed from cell survival assay with PC12 derived neuronal cells against Aβ42 induced neurotoxicity.

Protein immobilization on graphene oxide or reduced graphene oxide surface and their applications: Influence over activity, structural and thermal stability of protein

Due to the essential role of biological macromolecules in our daily life; it is important to control the stability and activity of such macromolecules. Therefore, the most promising route for enhancement in stability and activity is immobilizing proteins on different support materials. Furthermore, large surface area and surface functional groups are the important features that are required for a better support system. These features of graphene oxide (GO) and reduced graphene oxide (RGO) makes them ideal support materials for protein immobilization. Studies show the successful formation of GO/RGO-protein complexes with enhancement in structural/thermal stability due to various interactions at the nano-bio interface and their utilization in various functional applications. The present review focuses on protein immobilization using GO/RGO as solid support materials. Moreover, we also emphasized on basic underlying mechanism and interactions (hydrophilic, hydrophobic, electrostatic, local protein-protein, hydrogen bonding and van der Walls) between protein and GO/RGO which influences structural stability and activity of enzymes/proteins. Furthermore, GO/RGO-protein complexes are utilized in various applications such as biosensors, bioimaging and theranostic agent, targeted drug delivery agents, and nanovectors for drug and protein delivery.

Graphene Oxide Coatings as Tools to Prevent Microbial Biofilm Formation on Medical Device

The clinical challenge on surface engineering of medical devices to prevent microorganisms adhesion and biofilm formation, has become an essential aspect for medical implants. Antibacterial properties of Graphene Oxide (GO) have been demonstrated across a broad spectrum of bacteria, and the different mechanisms of action with which this nanomaterial interacts with the microbial surface have been elucidated in detail. Innovative protective coatings based on graphene film and hydrogel could represent an innovative solution for the prevention of nosocomial pathogens colonization on implantable device. This brief review mainly focuses on the applications of graphene in nanomedicine with a particular deepening on the antibacterial properties of GO and GO-based nanomaterials. In order to evaluate the possible future applications of GO as an anti-biofilm coating material for medical devices, studies on the ability of graphene coated surface to prevent microbial adhesion are also discussed. A concise review on in vitro toxicity and in vivo safety is also presented.

In-depth understanding of a nano-bio interface between lysozyme and Au NP-immobilized N-doped reduced graphene oxide 2-D scaffolds

In the present work, nitrogen-doped reduced graphene oxide (NrGO) was synthesized via a hydrothermal treatment of graphene oxide (GO) in the presence of urea. Gold nanoparticles (Au(0) NPs) were immobilized over the surface of NrGO (Au(0)-NrGO). Characterization of the Au(0)-NrGO nanocomposite via FT-IR spectroscopy, Raman spectroscopy, elemental mapping and XPS revealed the doping of N atoms during the reduction of GO. XRD and XPS studies confirmed the presence of Au(0) NPs and EDS analysis showed a 4.51 wt% loading of Au NPs in the Au(0)-NrGO nanocomposite. The morphology of Au(0)-NrGO was explored by SEM and TEM, which showed the presence of spherical Au metal NPs uniformly immobilized on the surface of NrGO. Further, studies on lysozyme (Lys) in the presence of Au(0)-NrGO by UV-visible, fluorescence, and circular dichroism spectroscopy revealed a conformational change in Lys and electrostatic interaction between Lys and Au(0)-NrGO. The DLS result showed an enhancement in the size of the Au(0)-NrGO and Lys conjugates. The Au(0)-NrGO-induced conformational changes in the structure of Lys resulted in a significant decrease in its activity at a certain concentration of Au(0)-NrGO. Moreover, the results showed that Lys favorably binds with the surface of Au(0)-NrGO, resulting in the formation of 2-D scaffolds possibly due to electrostatic and hydrophobic interactions, H-bonding, and interactions between the AuNPs and sulfur-containing amino acid residues of Lys. SEM exhibited the formation of conjugates in the form of 2-D scaffolds due to the biomolecular interactions between Lys and Au(0)-NrGO. The TEM studies revealed that Lys agglomerated around the Au(0) NPs immobilized on the surface of NrGO, which suggests the formation of a protein corona (PC) around the AuNPs. Furthermore, the favorable Au(0) NP-sulphur (PC) interaction was confirmed by the disappearance of the S-S stretching band in the Raman spectra. Overall, the results obtained provide insight into the nano-bio interface and formation of Au(0) NP-PC, which can be used for bioinspired applications, such as biosensing and imaging and the development of advanced functional Au NPs.