Biological synthesis of platinum nanoparticles with apoferritin

Protein encapsulation of nanocatalysts: A feasible approach to facilitate catalytic theranostics

Enzyme-mimicking nanocatalysts, also termed nanozymes, have attracted much attention in recent years. They are considered potential alternatives to natural enzymes due to their multiple catalytic activities and high stability. However, concerns regarding the colloidal stability, catalytic specificity, efficiency and biosafety of nanomaterials in biomedical applications still need to be addressed. Proteins are biodegradable macromolecules that exhibit superior biocompatibility and inherent bioactivities; hence, the protein modification of nanocatalysts is expected to improve their bioavailability to match clinical needs. The diversity of amino acid residues in proteins provides abundant functional groups for the conjugation or encapsulation of nanocatalysts. Moreover, protein encapsulation can not only improve the overall performance of nanocatalysts in biological systems, but also bestow materials with new features, such as targeting and retention in pathological sites. This review aims to report the recent developments and perspectives of protein-encapsulated catalysts in their functional improvements, modification methods and applications in biomedicine.

Preparation of platinum nanoparticles using iron(ii) as reductant and photosensitized H2 generation on an iron storage protein scaffold

The quest for efficient solar-to-fuel conversion has led to the development of numerous homogeneous and heterogeneous systems for photochemical stimulation of 2H⁺ + 2e⁻ → H₂. Many such systems consist of a photosensitizer, an H₂-evolving catalyst (HEC), and sacrificial electron donor often with an electron relay between photosensitizer and HEC. Colloidal platinum remains a popular HEC. We report here a novel, simple, and high yield synthesis of Pt nanoparticles (Pt NPs) associated with human heavy chain ferritin (Hfn). The formation of the Pt NPs capitalizes on Hfn's native catalysis of autoxidation of Fe(ii)(aq) (ferroxidase activity). Fe(ii) reduces Pt(ii) to Pt(0) and the rapid ferroxidase reaction produces FeO(OH), which associates with and stabilizes the incipient Pt NPs. This Pt/Fe-Hfn efficiently catalyzes photosensitized H₂ production when combined with Eosin Y (EY) as photosensitizer and triethanolamine (TEOA) as sacrificial electron donor. With white light irradiation turnover numbers of 300H₂ per Pt, 250H₂ per EY were achieved. A quantum yield of 18% for H₂ production was obtained with 550 nm irradiation. The fluorescence emission of EY is quenched by TEOA but not by Pt/Fe-Hfn. We propose that the photosensitized H₂ production from aqueous TEOA, EY, Pt/Fe-Hfn solution occurs via a reductive quenching pathway in which both the singlet and triplet excited states of EY are reduced by TEOA to the anion radical, EY⁻˙, which in turn transfers electrons to the Pt/Fe-Hfn HEC. Hfn is known to be a remarkably versatile scaffold for incorporation and stabilization of noble metal and semiconductor nanoparticles. Since both EY and Hfn are amenable to scale-up, we envision further refinements to and applications of this photosensitized H₂-generating system.

An assembly of platinum nanoparticles produced by Fe(ii) reduction of Pt(ii) and stabilized by human heavy chain ferritin's native catalysis of Fe(ii)(aq) autoxidation functions as an efficient photosensitized H₂ evolution catalyst.

Different platinum crystal surfaces show very distinct protein denaturation capabilities

Different platinum (Pt) surfaces of nanocrystals usually exhibit significant distinctions with regard to various biological, physical, and chemical characteristics, such as bio-recognition, surface wetting, and catalytic activities. In this study, we report for the first time that two shape-controlled Pt nanocrystals with the most common low-index surfaces, Pt(100) and Pt(111), show very dissimilar protein denaturation capabilities based on all-atom molecular dynamics simulations employing the widely used model protein, villin headpiece (HP35). We demonstrate that HP35 is well preserved on the Pt(100) crystal surface, whereas it is severely disrupted on the Pt(111) crystal surface. This surprising difference originates from the distinct water behavior in the first solvation shell (FSS) of the two Pt crystal surfaces. Within the FSS of the Pt(100) crystal surface, water molecules form a very compact and stable monolayer through a highly uniform rhombic hydrogen-bond network. This water monolayer prefers the adsorption of acidic residues (such as Glu and Asp) and acts as a shield to prevent other residues from directly coming into contact with the metal surface. On the other hand, the hydrogen bond network in the water monolayer in the FSS of the Pt(111) crystal surface is very sparse and quite defective, which makes it more vulnerable to the penetration of various residues, particularly those with planar side chains such as Phe, Trp and Arg due to strong dispersion interactions, leading to subsequent protein unfolding. The binding free energy calculations for some key amino acids on the two different crystal surfaces further uncover the molecular origin behind their distinct protein denaturation capability. Our study reveals the vital importance of interfacial water in determining the structure of proteins when binding to different metal crystal surfaces. The discovered molecular mechanisms may be helpful for the future development of a bio-assisted programmable synthetic strategy of sophisticated Pt nanostructures for biomedical applications.

Silver-gold-apoferritin nanozyme for suppressing oxidative stress during cryopreservation

Reactive oxygen species (ROS) cause oxidative stress, which involves in the pathogenesis of many serious diseases. Apoferittin containing gold-silver nanoparticles (Au-Ag-AFT) was designed and evaluated as a nanozyme for scavenging the ROS. The nanozyme consisting of silver-gold nanohybrid in apoferittin cage represents superoxide dismutase, catalase and peroxidase mimetic activities. The Au-Ag-AFT nanozyme was characterized by spectroscopy, FESEM, TEM and dynamic light scattering. The inhibition process for pyrogallol autoxidation was used for assaying the superoxide dismutase mimetic activity and measuring the kinetic parameters of Au-Ag-AFT nanozyme. Additionally, Aebi method and standard protocol was used for evaluating the catalase and peroxidase mimetic activity. The k_cat values for superoxide dismutase, catalase and peroxidase mimetics activity were 1.4 × 10⁶, 0.1 and 9 × 10³ s^-1 respectively. These values indicated that Au-Ag-AFT nanozyme could act as a suitable ROS scavenger. Additionally, Au-Ag-AFT nanozyme was examined as a protective agent for human sperm against oxidative stress induced during the cryopreservation process. Presence of the nanozyme in the sperm media significantly increased the motility and viability of the cells and also decreased the ROS, apoptosis and necrosis (P < 0.05) compare to the control group.

Platinum nanoparticles in nanobiomedicine

Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

An optimized low-cost protocol for standardized production of iron-free apoferritin nanocages with high protein recovery and suitable conformation for nanotechnological applications

Ferritin is a globular protein that consists of 24 subunits forming a hollow nanocage structure that naturally stores iron oxyhydroxides. Elimination of iron atoms to obtain the empty protein called apoferritin is the first step to use this organic shell as a nanoreactor for different nanotechnological applications. Different protocols have been reported for apoferritin formation, but some are time consuming, others are difficult to reproduce and protein recovery yields are seldom reported. Here we tested several protocols and performed a complete material characterization of the apoferritin products using size exclusion chromatography, UV-vis spectroscopy, inductively coupled plasma optical emission spectrometry and dynamic light scattering. Our best method removes more than 99% of the iron from loaded holoferritin, recovering 70-80% of the original protein as monomeric apoferritin nanocages. Our work shows that pH conditions of the reduction step and the presence and nature of chelating agents affect the efficiency of iron removal. Furthermore, process conditions also seem to have an influence on the monomer:aggregate proportion present in the product. We also demonstrate that iron contents markedly increase ferritin absorbance at 280nm. The influence of iron contents on absorbance at 280nm precludes using this simple spectrophotometric measure for protein determination in ferritin‑iron complexes. Apoferritin produced following our protocol only requires readily-available, cheap and biocompatible reagents, which makes this process standardizable, scalable and applicable to be used for in vivo applications of ferritin derivatives as well as nanotechnological and biotechnological uses.

Silver nanoparticles toxicity against airborne strains of Staphylococcus spp

The aim of this study was to explore the toxicity of silver nanoparticles (AgNPs) synthesized by chemical reduction method assessment with regard to airborne strains of Staphylococcus spp. The first step of the experiment was the preparation of silver nanoparticle suspension. The suspension was obtained by a fast and simple chemical method involving the reduction of silver ions through a reducing factor in the presence of the suitable stabilizer required to prevent the aggregation. In the second stage, varied instrumental techniques were used for the analysis and characterization of the obtained nanostructures. Third, the bacteria of the Staphylococcus genus were isolated from the air under stable conditions with 47 sports and recreational horses, relatively. Next, isolated strains were identified using biochemical and spectrophotometric methods. The final step was the evaluation of the Staphylococcus genus sensitivity to nanosilver using the disk diffusion test. It has been proven that prepared silver nanoparticles exhibit strong antibacterial properties. The minimum inhibitory concentration for tested isolates was 30 μg/mL. It has been found that the sensitivity of Staphylococcus spp. isolated from six identified species differs considerably. The size distribution of bacterial growth inhibition zones indicates that resistance to various nanosilver concentrations is an individual strain feature, and has no connection with belonging to a specific species.

Functional ferritin nanoparticles for biomedical applications

Ferritin, a major iron storage protein with a hollow interior cavity, has been reported recently to play many important roles in biomedical and bioengineering applications. Owing to the unique architecture and surface properties, ferritin nanoparticles offer favorable characteristics and can be either genetically or chemically modified to impart functionalities to their surfaces, and therapeutics or probes can be encapsulated in their interiors by controlled and reversible assembly/disassembly. There has been an outburst of interest regarding the employment of functional ferritin nanoparticles in nanomedicine. This review will highlight the recent advances in ferritin nanoparticles for drug delivery, bioassay, and molecular imaging with a particular focus on their biomedical applications.

Photosensitized H2 generation from "one-pot" and "two-pot" assemblies of a zinc-porphyrin/platinum nanoparticle/protein scaffold

We report photosensitized H2 generation using a protein scaffold that nucleates formation of platinum nanoparticles (Pt NPs) and contains "built-in" photosensitizers. The photosensitizers, zinc-protoporphyrin IX or zinc-mesoporphyrin IX (ZnP) were incorporated in place of the naturally occurring heme in the 24-subunit iron storage protein bacterioferritin (Bfr) when the ZnPs were added to the E. coli expression medium. We engineered a stable dimeric Bfr variant with two protein subunits sandwiching a ZnP. Ten glycines were also substituted in place of residues surrounding the vinyl side of the porphyrin in order increase access of solvent and/or redox agents. An optimized "one-pot" reaction of this glycine-substituted ZnMP-Bfr dimer with a Pt(iv) salt and borohydride resulted in a ∼50 : 50 mixture of protein in the form of Pt-free glycine-substituted ZnP-Bfr dimers and re-assembled 24-mers surrounding Pt NPs formed in situ. H2 production occurred upon visible light irradiation of this "one-pot" product when combined with triethanolamine as sacrificial electron donor and methyl viologen as electron relay. An analogous "two-pot" system containing mixtures of separately prepared Pt-free glycine-substituted ZnP-Bfr dimer and porphyrin-free Pt NP@Bfr 24-mer also showed robust photosensitized H2 generation. The glycine-substituted-ZnP-Bfr dimer thus served as photosensitizer for catalytic reduction of methyl viologen by triethanolamine, and the reduced methyl viologen was able to transfer electrons across the Bfr 24-mer protein shell to generate H2 at the enclosed Pt NP in a "dark" reaction. Our results demonstrate that Bfr is a readily manipulatable and versatile scaffold for photosensitized redox chemistry.

Computer simulations of the interaction of human immunodeficiency virus (HIV) aspartic protease with spherical gold nanoparticles: implications in acquired immunodeficiency syndrome (AIDS)

The interaction of gold nanoparticles (AuNP) with human immune-deficiency virus aspartic protease (HIVPR) is modelled using a regime of molecular dynamics simulations. The simulations of the 'docking', first as a rigid-body complex, and eventually through flexible-fit analysis, creates 36 different complexes from four initial orientations of the nanoparticle strategically positioned around the surface of the enzyme. The structural deviations of the enzymes from the initial x-ray crystal structure during each docking simulation are assessed by comparative analysis of secondary structural elements, root mean square deviations, B-factors, interactive bonding energies, dihedral angles, radius of gyration (R g), circular dichroism (CD), volume occupied by C α , electrostatic potentials, solvation energies and hydrophobicities. Normalisation of the data narrows the selection from the initial 36 to one 'final' probable structure. It is concluded that, after computer simulations on each of the 36 initial complexes incorporating the 12 different biophysical techniques, the top five complexes are the same no matter which technique is explored. The significance of the present work is an expansion of an earlier study on the molecular dynamic simulation for the interaction of HIVPR with silver nanoparticles. This work is supported by experimental evidence since the initial 'orientation' of the AgNP with the enzyme is the same as the 'final' AuNP-HIVPR complex generated in the present study. The findings will provide insight into the forces of the binding of the HIVPR to AuNP. It is anticipated that the protocol developed in this study will act as a standard process for the interaction of any nanoparticle with any biomedical target.

Multiple fold increase in activity of ferroxidase-apoferritin complex by silver and gold nanoparticles

The effect of silver (Ag) and gold (Au) nanoparticles on the ferroxidase activity of apoferritin showed a 110-fold increase in specific activity and a 9-fold increase over the control at the respective molar ratios of Au-apoferritin and Ag-apoferritin nanoparticles (NPs) of 500:1 and 1000:1. Typical color change, from pale yellow to brown, occurred when apoferritin was mixed with AgNO(3) or AuCl(3) followed by sodium borohydride to afford respective metal-apoferritin NP complexes in a ratio of between 250:1 and 4000:1. These complexes were characterized by ultraviolet-visible inductively coupled plasma-optical emission spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. Transmission electron microscopy revealed that the size of NPs increased as the molar ratio of metal to apoferritin increased, with an average size of 3-6 nm generated with Au-to-apoferritin and/or Ag-to-apoferritin molar ratios of 250:1 to 4000:1. Fourier transform infrared spectrometry showed no structural changes of apoferritin when the NPs were attached to the protein.

FROM THE CLINICAL EDITOR

In this paper the utility of gold and silver nanoparticles in augmenting the activity of the ferroxidase-apoferritin complex is described. Both NPs dramatically increased the ferroxidase activity.

Extracellular biosynthesis of platinum nanoparticles using the fungus Fusarium oxysporum

Nanoscience is a blooming field and promises a better future. In order to fabricate nanoparticles in an eco-friendly and inexpensive manner, significant efforts are being made to replace the chemical and physical methods currently being used with the biological methods. Chemical methods are toxic while the physical ones are very expensive. Biological methods, apart from being cost-effective, also provide protein capped nanoparticles which are thus very stable, have good dispersity and do not flocculate, and may find use in various applications. The present work emphasizes on platinum nanoparticles synthesis protocol which occurs at ambient conditions. The fungus Fusarium oxysporum when incubated with hexachloroplatinic acid (H(2)PtCl(6)) in ambient conditions reduces the precursor and leads to the formation of stable extracellular platinum nanoparticles. The biosynthesis of platinum nanoparticles was monitored by UV-visible spectroscopy and these nanoparticles were completely characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The nanoparticles are in the size range of 5-30 nm and are stabilized by proteins present in the solution. The reduction process is believed to occur enzymatically, thus creating the possibility of a rational, fungal-based method for the synthesis of nanoparticles over a wide range of chemical compositions.

Ferroxidase activity of apoferritin is increased in the presence of platinum nanoparticles

The ferroxidase activity of horse spleen apoferritin (HSAF) is increased by nine-fold in the presence of platinum nanoparticles. HSAF was mixed with varying concentrations of K2PtCl4 followed by a 20-fold concentration of sodium borohydride to afford Pt:HSAF nanoparticle complexes in a ratio of between 1:250 and 1:4000. Typical colour changes, from colourless or pale yellow to brown, occurred that were dependent on the amount of platinum present. These complexes were characterized by UV/vis, inductively coupled plasma optical emission spectroscopy, Fourier transform infrared, transmission electron microscopy and energy dispersive x-ray spectroscopy. Transmission electron microscopy analysis revealed that the size of nanoparticles increased as the molar ratio of platinum to HSAF increased with an average size diameter of 2-6 nm generated with HSAF:platinum molar ratios of 1:250-1:4000. Fourier transform infrared spectroscopy (FTIR) spectra showed no distinct changes in the structure of HSAF but confirmed that the nanoparticles were attached to the protein. The effect of platinum nanoparticles on the ferroxidase activity of HSAF showed a specific activity of 360 ρmol min(-1) mg(-1), (nine-fold increase over the control) at the molar ratio of HSAF:platinum nanoparticles of 1:1000.

Ferritin protein nanocages use ion channels, catalytic sites, and nucleation channels to manage iron/oxygen chemistry

The ferritin superfamily is composed of ancient, nanocage proteins with an internal cavity, 60% of total volume, that reversibly synthesize solid minerals of hydrated ferric oxide; the minerals are iron concentrates for cell nutrition as well as antioxidants due to ferrous and oxygen consumption during mineralization. The cages have multiple iron entry/exit channels, oxidoreductase enzyme sites, and, in eukaryotes, Fe(III)O nucleation channels with clustered exits that extend protein activity to include facilitated mineral growth. Ferritin protein cage differences include size, amino acid sequence, and location of the active sites, oxidant substrate and crystallinity of the iron mineral. Genetic regulation depends on iron and oxygen signals, which in animals includes direct ferrous signaling to RNA to release and to ubiquitin-ligases to degrade the protein repressors. Ferritin biosynthesis forms, with DNA, mRNA and the protein product, a feedback loop where the genetic signals are also protein substrates. The ferritin protein nanocages, which are required for normal iron homeostasis and are finding current use in the delivery of nanodrugs, novel nanomaterials, and nanocatalysts, are likely contributors to survival and success during the transition from anaerobic to aerobic life.

Reducing stress on cells with apoferritin-encapsulated platinum nanoparticles

The great potential for medical applications of inorganic nanoparticles in living organisms is severely restricted by the concern that nanoparticles can harmfully interact with biological systems, such as lipid membranes or cell proteins. To enable an uptake of such nanoparticles by cells without harming their membranes, platinum nanoparticles were synthesized within cavities of hollow protein nanospheres (apoferritin). In vitro, the protein-platinum nanoparticles show good catalytic efficiency and long-term stability. Subsequently the particles were tested after ferritin-receptor-mediated incorporation in human intestinal Caco-2 cells. Upon externally induced stress, for example, with hydrogen peroxide, the oxygen species in the cells decreased and the viability of the cells increased.