Conformation and activity of lysozyme on binding to two types of gold nanorods: A comparative study

Study on the molecular mechanism of gold nanorods interacting with fibrinogen and transferrin to form protein corona

The molecular mechanism of the formation of protein corona by the interaction of gold nanorods (AuNRs) with fibrinogen and transferrin was studied by spectroscopic methods and molecular docking. Studies have shown that AuNRs can be used as quencher to quench the fluorescence of fibrinogen/transferrin. The quenching mechanism mainly comes from static quenching. Fibrinogen has two different binding sites on the longitudinal and the transverse plane of AuNRs respectively, while transferrin has only one binding site on the surface of AuNRs. The adsorption process conforms to Freundlich adsorption isotherm and the pseudo-second-order reaction. The chemisorption is the rate-limiting step. Fibrinogen/transferrin may be a component of the "hard corona" because they bind AuNRs with high binding affinity. The formation of protein corona leads to a decrease in the hydrophobicity of the microenvironment around transferrin tryptophan (Trp) residues and an increase in the hydrophobicity of the microenvironment around fibrinogen/transferrin tyrosine (Tyr) residues, affecting the tertiary and secondary structure of fibrinogen/transferrin. Molecular docking can clearly see the specific amino acid residues of fibrinogen and transferrin adsorbed on AuNRs, and verify the experimental results.

Comparative analysis of the interaction mechanism of γ-globulin and hemoglobin with spherical and rod-shaped gold nanoparticles

The interaction mechanism of spherical gold nanoparticles (AuNPs) and rod-shaped gold nanoparticles (AuNRs) with γ-globulin and hemoglobin was comprehensively and comparatively analyzed. γ-Globulin and hemoglobin have high affinity with AuNPs, and with two different types of binding sites on AuNRs surface. Except hemoglobin interaction with the first binding site of AuNRs, the interaction between γ-globulin/hemoglobin and AuNPs/AuNRs is the spontaneous, endothermic and entropy-driven process, and hydrophobic interaction plays a dominant role. The molecular adsorption mechanism of γ-globulin/hemoglobin on AuNPs and AuNRs surface conforms to Langmuir model and Freundlich model, respectively. The kinetic molecular mechanism between them conforms to the pseudo-second-order model, and chemisorption is the rate-limiting step. AuNPs result in the loosening and unfolding of γ-globulin backbone. AuNRs have no significant effect on γ-globulin backbone. AuNPs/AuNRs result in no significant changes in hemoglobin structure and heme group microenvironment. AuNPs/AuNRs decrease the hydrophobicity of Trp microenvironment of γ-globulin, but there is an intramolecular energy transfer from Trp residue to Tyr residue of hemoglobin. The β-sheet of γ-globulin and the α-helix of hemoglobin reduce by increasing concentrations of AuNPs/AuNRs. Molecular docking is suggesting that the specific amino acid residues of γ-globulin and hemoglobin interaction with AuNPs/AuNRs, and validates the experimental results.

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Label-Free and Bioluminescence-Based Nano-Biosensor for ATP Detection

A bioluminescence-based assay for ATP can measure cell viability. Higher ATP concentration indicates a higher number of living cells. Thus, it is necessary to design an ATP sensor that is low-cost and easy to use. Gold nanoparticles provide excellent biocompatibility for enzyme immobilization. We investigated the effect of luciferase proximity with citrate-coated gold, silver, and gold-silver core-shell nanoparticles, gold nanorods, and BSA-Au nanoclusters. The effect of metal nanoparticles on the activity of luciferases was recorded by the luminescence assay, which was 3-5 times higher than free enzyme. The results showed that the signal stability in presence of nanoparticles improved and was reliable up to 6 h for analytes measurements. It has been suggested that energy is mutually transferred from luciferase bioluminescence spectra to metal nanoparticle surface plasmons. In addition, we herein report the 27-base DNA aptamer for adenosine-5'-triphosphate (ATP) as a suitable probe for the ATP biosensor based on firefly luciferase activity and AuNPs. Due to ATP application in the firefly luciferase reaction, the increase in luciferase activity and improved detection limits may indicate more stability or accessibility of ATP in the presence of nanoparticles. The bioluminescence intensity increased with the ATP concentration up to 600 µM with a detection limit of 5 µM for ATP.

The interaction mechanism between gold nanoparticles and proteins: Lysozyme, trypsin, pepsin, γ-globulin, and hemoglobin

In this study, the interaction between gold nanoparticles (AuNPs) and proteins (including lysozyme, trypsin, pepsin, γ-globulin and hemoglobin) was investigated by UV-visible absorption spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy and protein activity assay. AuNPs was synthesized using reduction of HAuCl₄ with sodium citrate. The formation of AuNPs was confirmed from the characteristic surface plasmon resonance band at 521 nm and transmission electron microscopy revealed the average particle size was about 10 nm. The results reveal that AuNPs can interact with proteins to form a "protein corona (PC)", but the protein concentration required to form a relatively stable PC is not the same. The quenching mechanism of proteins by AuNPs is arisen from static quenching. The binding constants of AuNPs with proteins are in the range from 10⁶ to 10¹⁰ L mol^-1, and the order is pepsin > γ-globulin > hemoglobin > trypsin > lysozyme at 298 K. Van der Waals forces and hydrogen bonds are the main forces for the lysozyme-AuNPs system. The interaction between trypsin/pepsin/γ-globulin/hemoglobin and AuNPs is mainly by hydrophobic interaction. The addition of AuNPs has an effect on the secondary structure of proteins as confirmed from CD spectra. The change in secondary structure of different proteins is different and seems to have little relation with the binding constant. The activity of lysozyme/trypsin/pepsin decreases with the addition of AuNPs.

Gold Nanorods for Drug and Gene Delivery: An Overview of Recent Advancements

Over the past few decades, gold nanomaterials have shown great promise in the field of nanotechnology, especially in medical and biological applications. They have become the most used nanomaterials in those fields due to their several advantageous. However, rod-shaped gold nanoparticles, or gold nanorods (GNRs), have some more unique physical, optical, and chemical properties, making them proper candidates for biomedical applications including drug/gene delivery, photothermal/photodynamic therapy, and theranostics. Most of their therapeutic applications are based on their ability for tunable heat generation upon exposure to near-infrared (NIR) radiation, which is helpful in both NIR-responsive cargo delivery and photothermal/photodynamic therapies. In this review, a comprehensive insight into the properties, synthesis methods and toxicity of gold nanorods are overviewed first. For the main body of the review, the therapeutic applications of GNRs are provided in four main sections: (i) drug delivery, (ii) gene delivery, (iii) photothermal/photodynamic therapy, and (iv) theranostics applications. Finally, the challenges and future perspectives of their therapeutic application are discussed.

Optical characterization and tunable antibacterial properties of gold nanoparticles with common proteins

The interaction of three proteins, viz. Bovine Serum Albumin (BSA), Human Serum Albumin (HSA) and Hen Egg White Lysozyme (HEWL) with gold nanoparticles (GNPs) is investigated using surface plasmon resonance (SPR) spectroscopy, fluorescence spectroscopy and circular dichroism (CD). Size and morphology of the samples was established using Transmission Electron Microscopy (TEM) and stability studies was established using zeta potential analysis. The stability of protein-GNP complex was found to be greater than that of individual protein as well as individual GNPs. Also HEWL-GNP complex was more stable compared to the other protein complexes. Absorbance of proteins increases with increase in gold nanoparticle concentration due to the extension of peptide strands of protein and decrease in hydrophobicity of gold nanoparticles. A ground state complex is also formed which is evident from the moderate shift observed in the absorbance peaks. Apparent association constant was also determined from the absorption spectra and was found to be maximum for HEWL and minimum for HSA. Gold nanoparticles were found to act as quenchers and reduced the protein fluorescence intensity. Binding constant and number of binding sites were found to be maximum for HEWL and minimum for HSA. The temperature dependent fluorescence studies were also performed to calculate the thermodynamic parameters and to determine the nature of interaction between the proteins and gold nanoparticles. The circular dichroism studies elucidate the reason behind the maximum binding for HEWL and minimum binding for HSA. TGA analysis determined the thermal stability of the samples. Fluorescence lifetime studies indicate static quenching of proteins. Antibacterial activity of protein-gold nanoparticles was studied against four pathogens, viz. Bacillus pumilus, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. HEWL exhibits a tunable antimicrobial activity against Pseudomonas aeruginosa due to the maximum binding of HEWL with gold nanoparticles. The study proposes a novel method for adjusting the antibacterial activity of HEWL against Pseudomonas aeruginosa when the resistance of this pathogen is a major issue in the chemotherapy of many infectious diseases. Thus the combination therapy of protein-gold nanoparticles could prove to be a new approach in medical field in the near future.

Synthesis and Characterization of Selenium Nanoparticles-Lysozyme Nanohybrid System with Synergistic Antibacterial Properties

In the light of promising potency of selenium nanoparticles in biomedical applications, this is the first study to report the synergistic antibacterial activity of these nanoparticles and lysozyme. The nanohybrid system was prepared with various concentrations of each component. Resistance of Escherichia coli and Staphylococcus aureus was compared in the presence of individual Nano and Bio counterparts as well as the nanohybrid system. Upon interaction of SeNPs with Lysozyme, the nanohybrid system efficiently enhanced the antibacterial activity compared to the protein. Therefore, SeNPs play an important role in inhibition of bacterial growth at very low concentrations of protein; whereas very high amount of the protein is required to inhibit bacterial growth individually. On the other hand, lysozyme has also played a vital role in antibacterial property of SeNPs, inducing 100% inhibition at very low concentration of each component. Hence, presence of both nano and bio counterparts induced vital interplay in the Nanohybrid system. The aged samples also presented good stability of SeNPs both as the intact and complex form. Results of this effort highlight design of nanohybrid systems with synergistic antibacterial properties to overcome the emerging antibiotic resistance as well as to define fruitful applications in biomedicine and food safety.

Graphene Oxide and Lysozyme Ultrathin Films with Strong Antibacterial and Enhanced Osteogenesis

There is a great demand worldwide for bone-related implant materials. The drawbacks of chronic infections and poor bone healing of current implant materials have limited their clinical applications. Functionalizing the implant surfaces with antibacterial and osteogenic films on implant materials provides new opportunities for fabricating novel implant materials. In the present study, an ultrathin (GO/Lys)₈ film of several tens of nanometers was fabricated using a layer-by-layer (LBL) technique with alternative deposition of graphene oxide (GO) and lysozyme (Lys). The deposition of the (GO/Lys) _n film exhibited a successive growth as supported by ellipsometry, UV-vis, and Fourier transform infrared data, and the physical properties (morphology, roughness, and stiffness) of this film were characterized with an atomic force microscope. The ultrathin films exhibited a great effect on bacterium sterilization of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and enhanced osteogenic differentiation efficiency, showing the potential application in bone implant coatings. We believe that this LBL assembling strategy will pave the way for fabricating dual-functional surfaces and guide the design of the implanted surfaces in the future.

Assembly of Gold Nanorods on HSA Amyloid Fibrils to Develop a Conductive Nanoscaffold for Potential Biomedical and Biosensing Applications

Today, Gold Nanorods have promised variety of applications in conjugation with biomolecules of interest. Discovery of functional amyloids has also been highlighted with possible use in designing high performance materials. To exploit dual properties of both Nano and Bio counterparts in new functional materials, this effort has focused on synthesis of a potential hybrid system of Gold nanorods (GNRs) and HSA amyloid fibrils to develop a conductive nanoscaffold. UV-Vis spectroscopy, Thioflavin T (ThT) assay, Far-UV Circular Dichroism (CD) spectropolarimetry, fluorescence and Transmission Electron microscopy were used to characterize formation of the nanostructures and amyloid fibrils. Surface plasmon resonance of GNRs was also monitored upon interaction with HSA amyloid fibrils, showing that the plasmonic component of the hybrid system has maintained its characteristic rod morphology without any perturbations. Analysis of Nyquist plots for the hybrid nanoscaffold showed that the electronic behavior of the hybrid system has been enhanced due to the presence of the assembled GNRs. Results of this investigation highlight the possibility of fabricating hybrid nano-bioscaffolds as promising candidates in versatile biomedical and biosensing applications.

Lysozyme Photochemistry as a Function of Temperature. The Protective Effect of Nanoparticles on Lysozyme Photostability

The presence of aromatic residues and their close spatial proximity to disulphide bridges makes hen egg white lysozyme labile to UV excitation. UVB induced photo-oxidation of tryptophan and tyrosine residues leads to photochemical products, such as, kynurenine, N-formylkynurenine and dityrosine and to the disruption of disulphide bridges in proteins. We here report that lysozyme UV induced photochemistry is modulated by temperature, excitation power, illumination time, excitation wavelength and by the presence of plasmonic quencher surfaces, such as gold, and by the presence of natural fluorescence quenchers, such as hyaluronic acid and oleic acid. We show evidence that the photo-oxidation effects triggered by 295 nm at 20°C are reversible and non-reversible at 10°C, 25°C and 30°C. This paper provides evidence that the 295 nm damage threshold of lysozyme lies between 0.1 μW and 0.3 μW. Protein conformational changes induced by temperature and UV light have been detected upon monitoring changes in the fluorescence emission spectra of lysozyme tryptophan residues and SYPRO® Orange. Lysozyme has been conjugated onto gold nanoparticles, coated with hyaluronic acid and oleic acid (HAOA). Steady state and time resolved fluorescence studies of free and conjugated lysozyme onto HAOA gold nanoparticles reveals that the presence of the polymer decreased the rate of the observed photochemical reactions and induced a preference for short fluorescence decay lifetimes. Size and surface charge of the HAOA gold nanoparticles have been determined by dynamic light scattering and zeta potential measurements. TEM analysis of the particles confirms the presence of a gold core surrounded by a HAOA matrix. We conclude that HAOA gold nanoparticles may efficiently protect lysozyme from the photochemical effects of UVB light and this nanocarrier could be potentially applied to other proteins with clinical relevance. In addition, this study confirms that the temperature plays a critical role in the photochemical pathways a protein enters upon UV excitation.

Heat induced aggregation of gold nanorods for rapid visual detection of lysozyme

Gold nanorods have been nominated as propitious candidates for nanobiodiagnostic applications. Herein, a technique has been introduced for rapid visual detection of lysozyme, as its high level of excretion in biological fluids is a characteristic sign of leukemia and kidney disorders. Gold nanorods were biofunctionalized with lysozyme aptamer and characterized with UV-Visible and FTIR spectroscopy, zeta potential analyzer and transmission electron microscopy. Exposure of the nanoprobe to nano molar levels of lysozyme (20 nmol l(-1)) lead to dictated aggregation of the nanostructures at ambient temperature; which was significantly improved by heat induced morphological perturbations and rapid detection by the naked eye (down to pico molar level). Qualitative analysis of Acute myeloid leukemia, Acute lymphocytic leukemia and Lymphoma blood serums showed sensitivity and specificity of the fabricated aptasensor under both temperature conditions. This report encourages utilization of heat-induced aggregation of gold nanorods as a promising nanodiagnostic technique for the emerging nanotechnologies.