Ferritin Molecules Research Articles

Construction of robust protein nanocage by designed disulfide bonds for active cargo molecules protection in the gastric environment

Notwithstanding the progress made, cargo molecules encapsulated within ferritin via oral administration in the gastric environment remains a persistent challenge. This study focuses on the strategic enhancement of ferritin stability in harsh gastric environment. By taking advantagie of computational-assisted design, we strategically introduced up to 96 disulfide bonds along three key inter-subunit interfaces to one single ferritin molecule with human H-chain ferritin and shrimp (Marsupenaeus japonicus) ferritin as starting materials, producing two kinds of robust ferritin nanocages with markedly enhanced acid and protease (pepsin and rennin) resistance. The crystal structure of ferritin nanocage confirmed our design at an atomic level. Encapsulation experiments demonstrated successful loading of bioactive cargo molecules (e.g., doxorubicin) into the engineered ferritin nanocages, with pronouncedly improved protection against leakage under acidic condition and the presence of pepsin and rennin as compared to their native counterparts. This study presents a potential approach for the design and engineering of protein nanocages for oral administration.

Construction of An Artificial Photosynthesis System with A Single CdS QDs-Ferritin Hybrid Molecule.

Establishing artificial photosynthesis systems in a simple but effective manner to mitigate the greenhouse effect and address the energy crisis remains challenging. The combination of photocatalysis technology with bioengineering is an emerging field with great potential to construct such artificial photosynthesis systems, but so far, it has barely been explored in this area. Herein, an artificial photocatalysis platform is constructed with high CO2 conversion and H2O splitting capability by integration of CdS QDs into the intra-subunit interface of H-type ferritin (Marsupenaeus japonicus), a natural ferroxidase through protein interface redesign. The crystal structure of the synthesized CdS QDs with engineered ferritin molecules as bio-templates confirmed the design at an atomic level. Notably, upon absorbing desirable visible light (≈420nm), such a single CdS-ferritin hybrid molecule is able to selectively catalyze the reduction of CO2 into HCOOH (≈90%), meanwhile catalyzing the oxidation of H2O into O2 in an aqueous environment. The O2 production rate reached to 180µmolg-1h-1, and the HCOOH output hit almost 800µmolg-1h-1. This work advances the utilization of the four-helix bundle structure for crafting artificial photosynthesis systems, facilitating the seamless integration of bioengineering and photocatalysis technology.

The crystal structure of Acinetobacter baumannii bacterioferritin reveals a heteropolymer of bacterioferritin and ferritin subunits

Iron storage proteins, e.g., vertebrate ferritin, and the ferritin-like bacterioferritin (Bfr) and bacterial ferritin (Ftn), are spherical, hollow proteins that catalyze the oxidation of Fe2+ at binuclear iron ferroxidase centers (FOC) and store the Fe3+ in their interior, thus protecting cells from unwanted Fe3+/Fe2+ redox cycling and storing iron at concentrations far above the solubility of Fe3+. Vertebrate ferritins are heteropolymers of H and L subunits with only the H subunits having FOC. Bfr and Ftn were thought to coexist in bacteria as homopolymers, but recent evidence indicates these molecules are heteropolymers assembled from Bfr and Ftn subunits. Despite the heteropolymeric nature of vertebrate and bacterial ferritins, structures have been determined only for recombinant proteins constituted by a single subunit type. Herein we report the structure of Acinetobacter baumannii bacterioferritin, the first structural example of a heteropolymeric ferritin or ferritin-like molecule, assembled from completely overlapping Ftn homodimers harboring FOC and Bfr homodimers devoid of FOC but binding heme. The Ftn homodimers function by catalyzing the oxidation of Fe2+ to Fe3+, while the Bfr homodimers bind a cognate ferredoxin (Bfd) which reduces the stored Fe3+ by transferring electrons via the heme, enabling Fe2+ mobilization to the cytosol for incorporation in metabolism.

Effect of Various Carbon Electrodes on MIP-Based Sensing Proteins Using Poly(Scopoletin): A Case Study of Ferritin.

Sensitivity in the sub-nanomolar concentration region is required to determine important protein biomarkers, e.g., ferritin. As a prerequisite for high sensitivity, in this paper, the affinity of the functional monomer to the macromolecular target ferritin in solution was compared with the value for the respective molecularly imprinted polymer (MIP)-based electrodes, and the influence of various surface modifications of the electrode was investigated. The analytical performance of ferritin sensing was investigated using three different carbon electrodes (screen-printed carbon electrodes, single-walled-carbon-nanotube-modified screen-printed carbon electrodes, and glassy carbon electrodes) covered with a scopoletin-based MIP layer. Regardless of the electrode type, the template molecule ferritin was mixed with the functional monomer scopoletin, and electropolymerization was conducted using multistep amperometry. All stages of MIP preparation were followed by evaluating the diffusional permeability of the redox marker ferricyanide/ferrocyanide through the polymer layer by differential pulse voltammetry. The best results were obtained with glassy carbon electrodes. The MIP sensor responded up to 0.5 µM linearly with a Kd of 0.30 µM. Similar results were also obtained in solution upon the interaction of scopoletin and ferritin using fluorescence spectroscopy, resulting in the quenching of the scopoletin signal, with a calculated Kd of 0.81 µM. Moreover, the binding of 1 µM ferritin led to 49.6% suppression, whereas human serum albumin caused 8.6% suppression.

Quantitative susceptibility mapping in the brain reflects spatial expression of genes involved in iron homeostasis and myelination.

Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying pattern of accumulation in the brain across individuals. The highest regions of accumulation are the deep grey nuclei, where iron is stored in paramagnetic molecule ferritin. This form of iron is considered to be what largely contributes to the signal measured by QSM in the deep grey nuclei. It is also known that QSM is affected by diamagnetic myelin contents. Here, we investigate spatial gene expression of iron and myelin related genes, as measured by the Allen Human Brain Atlas, in relation to QSM images of age-matched subjects. We performed multiple linear regressions between gene expression and the average QSM signal within 34 distinct deep grey nuclei regions. Our results show a positive correlation (p < .05, corrected) between expression of ferritin and the QSM signal in deep grey nuclei regions. We repeated the analysis for other genes that encode proteins thought to be involved in the transport and storage of iron in the brain, as well as myelination. In addition to ferritin, our findings demonstrate a positive correlation (p < .05, corrected) between the expression of ferroportin, transferrin, divalent metal transporter 1, several gene markers of myelinating oligodendrocytes, and the QSM signal in deep grey nuclei regions. Our results suggest that the QSM signal reflects both the storage and active transport of iron in the deep grey nuclei regions of the brain.

Preparation and Unique Three-Dimensional Self-Assembly Property of Starfish Ferritin.

The structure and assembly properties of ferritin derived from aquatic products remain to be explored. Constructing diverse three-dimensional (3D) protein architectures with the same building blocks has important implications for nutrient delivery, medicine and materials science. Herein, ferritin from Asterias forbesii (AfFer) was prepared, and its crystal structure was resolved at 1.91 Å for the first time. Notably, different from the crystal structure of other reported ferritin, AfFer exhibited a BCT lattice arrangement in its crystals. Bioinspired by the crystal structure of AfFer, we described an effective approach for manufacturing 3D porous, crystalline nanoarchitectures by redesigning the shared protein interface involved in different 3D protein arrays. Based on this strategy, two 3D superlattices of body-centered tetragonal and simple cubicwere constructed with ferritin molecules as the building blocks. This study provided a potentially generalizable strategy for constructing different 3D protein-based crystalline biomaterials with the same building blocks.

Iron in multiple sclerosis - Neuropathology, immunology, and real-world considerations.

Iron is an essential element involved in a multitude of bodily processes. It is tightly regulated, as elevated deposition in tissues is associated with diseases such as multiple sclerosis (MS). Iron accumulation in the central nervous system (CNS) of MS patients is linked to neurotoxicity through mechanisms including oxidative stress, glutamate excitotoxicity, misfolding of proteins, and ferroptosis. In the past decade, the combination of MRI and histopathology has enhanced our understanding of iron deposition in MS pathophysiology, including in the pro-inflammatory and neurotoxicity of iron-laden rims of chronic active lesions. In this regard, iron accumulation may not only have an impact on different CNS-resident cells but may also promote the innate and adaptive immune dysfunctions in MS. Although there are discordant results, most studies indicate lower levels of iron but higher amounts of the iron storage molecule ferritin in the circulation of people with MS. Considering the importance of iron, there is a need for evidence-guided recommendation for dietary intake in people living with MS. Potential novel therapeutic approaches include the regulation of iron levels using next generation iron chelators, as well as therapies to interfere with toxic consequences of iron overload including antioxidants in MS.

New iron export pathways acting via holo-ferritin secretion

Ferritin is a spherical nanocage protein for iron storage, composed of 24 light- or heavy-polypeptide chain subunits. A single ferritin molecule can carry up to 4500 iron atoms in its core, which plays an important role in suppressing intracellular iron toxicity. Serum ferritin levels are used as a marker for the total amount of iron stored in the body. Most serum ferritin is iron-free (apo-ferritin) and it is unclear how ferritin is released from cells. Ferritin is secreted into serum via extracellular vesicles (EVs) or the secretory autophagy pathway but not via the classical endoplasmic reticulum (ER)-to-Golgi secretion pathway. We recently discovered that the level of tetraspanin CD63, a common EV marker, is post-transcriptionally regulated by the intracellular iron level and both CD63 and ferritin expression is induced by iron loading. Ferritin is incorporated into CD63(+)-EVs through the ferritin-specific autophagy adapter molecule, NCOA4, and then secreted from cells. EV production differs drastically depending on cell type and physiological conditions. Extracellular matrix detached cells express pentaspanin prominin 2 and prominin 2(+)-EVs secrete ferritin independently of NCOA4 trafficking. Ferritin is tightly bound to iron in EVs and functions as an iron-carrier protein in the extracellular environment. Cells can suppress ferroptosis by secreting holo-ferritin, which reduces intracellular iron concentration. However, this exposes the neighboring cells receiving the secreted holo-ferritin to a large excess of iron. This results in cellular toxicity through increased generation of reactive oxygen species (ROS). Here we review the machinery by which ferritin is incorporated into EVs and its role as an intercellular communication molecule.

Constitutive Loss of Ptpn2 in Mice Causes Features of Anemia Including Iron Deficiency

Background: Anemia is the most frequent extraintestinal manifestation of inflammatory bowel disease (IBD) and is associated with the risk of Crohn’s disease. Anemia significantly impairs quality of life, increases hospitalization rates, and increases medical care costs of IBD patients. Iron deficiency is the most frequent cause of anemia in IBD; however, the mechanisms involved are still poorly understood. Here, we investigated the role of the IBD risk gene, protein tyrosine phosphatase non-receptor type 2 ( PTPN2), in regulating iron homeostasis. Methods: Constitutive Ptpn2 wild type (WT), heterozygous (Het), and knockout (KO) 3-week-old mice were analyzed for serum iron content, complete blood count parameters, and intestinal and extraintestinal non-heme iron. Protein and RNA from duodenal epithelial cells (DECs) were assayed by western blotting and qPCR. Localization of the brush border ferrous iron transporter, DMT1, and the ferrous iron absorption driver, NHE3, in duodenal tissue was determined by immunohistochemistry (IHC). Results: Ptpn2-KO mice had reduced i) serum iron ( p=0.0007; n=10); ii) serum iron carrier transferrin saturation ( p=0.0077; n=8); iii) hemoglobin ( p=0.0002; n=5); iv) hematocrit ( p=0.0023; n=5); v) intestinal non-heme iron: duodenum ( p=0.0128; n=10) and jejunum ( p=0.0006; n=8); and vi) extraintestinal tissue non-heme iron: liver ( p=0.0014; n=10), spleen ( p=0.04; n=10), kidney ( p=0.0004; n=7), and gastrocnemius muscle ( p=0.0436; n=9) vs. Ptpn2-WT and Het mice. This indicated that loss of Ptpn2 causes characteristics of anemia including decreased serum iron and tissue iron storage and impaired intestinal iron homeostasis. DEC gene expression of the intracellular iron storage molecule ferritin ( Fth1) was reduced ( p=0.048; n=4) while the basolateral cellular iron importer transferrin receptor 1 ( Tfrc1) was significantly increased ( p=0.0048; n=5) in Ptpn2-KO mice. Reduced FTH1 protein expression ( p=0.007; n=12) and increased TFRC1 protein expression ( p=0.0021; n=8) in DECs of Ptpn2-KO mice was confirmed by western blot, indicating cellular iron deficiency. DMT1 (n=6) and NHE3 (n=8) protein expression in DECs was unaltered, whereas IHC showed reduced apical membrane DMT1 and NHE3 in the duodenal epithelium of Ptpn2-KO mice (n=6), suggesting a possible mechanism of impaired intestinal non-heme iron uptake. Conclusions: Loss of Ptpn2 in mice causes features of anemia including iron deficiency associated with mislocalization of DMT1 and reduced apical membrane expression of NHE3. These findings identify a critical role for PTPN2 in regulating systemic iron homeostasis. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The significance of ferritin as one of the markers of inflammation

Iron is an extremely important trace element that plays a large role in oxygen transport, DNA synthesis and muscle tissue metabolism. Ferritin is a protein compound inwhich iron is deposited as a reserve for the body; in laboratory diagnostics, it is usually evaluated as a marker of iron content, and the determination of its concentration is used to diagnose iron deficiency conditions. It structurally consists of the protein apoferritin and the ferric atom in the composition of phosphate hydroxide. One ferritin molecule can contain up to 4,000 iron atoms. The ferritin content in blood is measured in nanograms per milliliter. The normal concentration for men is 29–397 ng/ml, and for women, it is 6–159 ng/ml. A decrease in the level of ferritin in the blood is possible in iron deficiency, but an increase in its concentration may indicate not only the development of hemochromatosis, but also, along with C-reactive protein, be a marker of an active inflammatory reaction. An increase in the synthesis of C-reactive protein, fibrinogen, ferritin, serum amyloid by hepatocytes occurs under the influence of pro-inflammatory cytokines IL-6, IL-18, IL-1, TNF in severe acute processes, especially in the case of their viral etiology.

Shrimp ferritin greatly improves the physical and chemical stability of astaxanthin.

The low stability of trans-astaxanthin (AX) not only limits its applications as a functional factor in food systems, but also affects the sensor quality of most shrimp products. Therefore, it is important to find an easy, effective way to improve the physical and chemical stability of AX. In this study, by taking advantage of the co-existence of AX and shrimp ferritin (Marsupenaeus japonicus ferritin, MjF), we investigated the interaction of AX with MjF. Results showed that AX molecules are able to bind on the outer surface of MjF to form complexes, and quantitative analyses demonstrated that one ferritin molecule is bound to ∼48 AX molecules. Consequently, such binding not only greatly enhances the water solubility, thermal stability, and photo stability of AX, but also protects AX from Fe2+ -induced oxidative damage, as compared to free AX. Thus, MjF could be used as a protective molecule to improve the physical and chemical stability of AX. PRACTICAL APPLICATION: Our study opens up a new avenue for improving the physicochemical properties of bioactive molecules by interacting with protein, and shrimp ferritin could be explored as a protective system for the bioactive molecules.

Pathogenic mechanism and modeling of neuroferritinopathy.

Neuroferritinopathy is a rare autosomal dominant inherited movement disorder caused by alteration of the L-ferritin gene that results in the production of a ferritin molecule that is unable to properly manage iron, leading to the presence of free redox-active iron in the cytosol. This form of iron has detrimental effects on cells, particularly severe for neuronal cells, which are highly sensitive to oxidative stress. Although very rare, the disorder is notable for two reasons. First, neuroferritinopathy displays features also found in a larger group of disorders named Neurodegeneration with Brain Iron Accumulation (NBIA), such as iron deposition in the basal ganglia and extrapyramidal symptoms; thus, the elucidation of its pathogenic mechanism may contribute to clarifying the incompletely understood aspects of NBIA. Second, neuroferritinopathy shows the characteristic signs of an accelerated process of aging; thus, it can be considered an interesting model to study the progress of aging. Here, we will review the clinical and neurological features of neuroferritinopathy and summarize biochemical studies and data from cellular and animal models to propose a pathogenic mechanism of the disorder.

Near-Field Nanoscopic Terahertz Imaging of Single Proteins.

Terahertz (THz) biological imaging has attracted intense attention due to its capability of acquiring physicochemical information in a label-free, noninvasive, and nonionizing manner. However, extending THz imaging to the single-molecule level remains a challenge, partly due to the weak THz reflectivity of biomolecules with low dielectric constants. Here, the development of graphene-mediated THz scattering-type scanning near-field optical microscope for direct imaging of single proteins is reported. Importantly, it is found that a graphene substrate with high THz reflectivity and atomic flatness can provide high THz contrast against the protein molecules. In addition, a platinum probe with an optimized shaft length is found enabling the enhancement of the amplitude of the scattered THz near-field signals. By coupling these effects, the topographical and THz scattering images of individual immunoglobulin G (IgG) and ferritin molecules with the size of a few nanometers are obtained, simultaneously. The demonstrated strategy thus opens new routes to imaging single biomolecules with THz.

Structural Insight into Binary Protein Metal-Organic Frameworks with Ferritin Nanocages as Linkers and Nickel Clusters as Nodes.

Metal-organic frameworks (MOFs) hold great promise for numerous applications. However, proteins, carriers of biological functions in living systems, have not yet been fully explored as building blocks for the construction of MOFs. This work presents a strategy for the fabrication of binary MOFs. Considering octahedral ferritin symmetry, four His2 (His-His) motifs were first incorporated into the exterior surface of a ferritin nanocage near each C4 channel, yielding protein linkers with multiple metal-binding sites (bisH-SF). Secondly, by adding nickel ions to bisH-SF solutions triggers the self-assembly of ferritin nanocages into a porous 3D crystalline MOF with designed protein lattice, where two adjacent ferritin molecules along the C4 symmetry axes are bridged by four dinuclear or tetranuclear nickel clusters depending on Ni2+ concentration. This work provides a simple approach for precise control over a binary protein-metal crystalline framework, and the resulting MOFs exhibited inherent ferroxidase activity and peroxidase-like catalytic activity.

Robust ultraclean atomically thin membranes for atomic-resolution electron microscopy

The fast development of high-resolution electron microscopy (EM) demands a background-noise-free substrate to support the specimens, where atomically thin graphene membranes can serve as an ideal candidate. Yet the preparation of robust and ultraclean graphene EM grids remains challenging. Here we present a polymer- and transfer-free direct-etching method for batch fabrication of robust ultraclean graphene grids through membrane tension modulation. Loading samples on such graphene grids enables the detection of single metal atoms and atomic-resolution imaging of the iron core of ferritin molecules at both room- and cryo-temperature. The same kind of hydrophilic graphene grid allows the formation of ultrathin vitrified ice layer embedded most protein particles at the graphene-water interface, which facilitates cryo-EM 3D reconstruction of archaea 20S proteasomes at a record high resolution of ~2.36 Å. Our results demonstrate the significant improvements in image quality using the graphene grids and expand the scope of EM imaging.

PH-depended protein shell dis- and reassembly of ferritin nanoparticles revealed by atomic force microscopy

Ferritin, a protein that is present in the human body for a controlled iron storage and release, consists of a ferrihydrite core and a protein shell. Apoferritin, the empty shell of ferritin, can be modified to carry tailored properties exploitable for targeted and direct drug delivery. This protein shell has the ability to dis- and reassemble depending on the pH value of the liquid environment and can thus be filled with the desired substance. Here we observed the dis- and reassembly process of the protein shell of ferritin and apoferritin in situ and in real space using atomic force microscopy. Ferritin and apoferritin nanoparticles adsorbed on a mica substrate exhibited a change in their size by varying the pH value of the surrounding medium. Lowering the pH value of the solution led to a decrease in size of the nanoparticles whereas a successive increase of the pH value increased the particle size again. The pH dependent change in size could be related to the dis- and reassembling of the protein shell of ferritin and apoferritin. Supplementary imaging by bimodal magnetic force microscopy of ferritin molecules accomplished in air revealed a polygonal shape of the core and a three-fold symmetry of the protein shell providing valuable information about the substructure of the nanoparticles.

Dual-probe (colorimetric and fluorometric) detection of ferritin using antibody-modified gold@carbon dot nanoconjugates.

A dual-mode assay is described for immunological determination of the anemia biomarker ferritin. It is based on the use of a gold@carbon dot (Au@CD) nanoconjugate as a colorimetric and fluorescent probe. Au@CD is hydrophilic, easily surface modified and stable in aqueous solution. The Au@CD have a red color with blue-green fluorescence and were modified with antibody against ferritin. This allows bi-modal detection of ferritin. Assays can be performed in phosphate buffer and were also analyzed in (Bovine Serum Albumin) BSA and (Fetal Bovine Serum) FBS. Detection is based on antigen-antibody interaction underlying the classical sandwich model. Response to ferritin can be detected by spectrophotometry (at 570nm) or fluorescence (at excitation/emission maxima of 354/454nm). Under optimal conditions, the assay has a linear response in the 1 to 120ngmL-1 ferritin concentration range and detection limits of 20 ng (colorimetrically) and 64ng (fluorometrically). Graphical abstract Schematic representation of the function of the designed nanoprobe. The Au@CD nanoconjugates are functionalized with ferritin antibody in the initial step which specifically interacts with ferritin molecules leading to aggregation and subsequent changes in the optical and fluorescence signals.

Iron concentrations in neurons and glial cells with estimates on ferritin concentrations

BackgroundBrain iron is an essential as well as a toxic redox active element. Physiological levels are not uniform among the different cell types. Besides the availability of quantitative methods, the knowledge about the brain iron lags behind. Thereby, disclosing the mechanisms of brain iron homeostasis helps to understand pathological iron-accumulations in diseased and aged brains. With our study we want to contribute closing the gap by providing quantitative data on the concentration and distribution of iron in neurons and glial cells in situ. Using a nuclear microprobe and scanning proton induced X-ray emission spectrometry we performed quantitative elemental imaging on rat brain sections to analyze the iron concentrations of neurons and glial cells.ResultsNeurons were analyzed in the neocortex, subiculum, substantia nigra and deep cerebellar nuclei revealing an iron level between (0.53pm 2) and (0.68pm 2),upmu hbox {M}. The iron concentration of neocortical oligodendrocytes is fivefold higher, of microglia threefold higher and of astrocytes twofold higher compared to neurons. We also analyzed the distribution of subcellular iron concentrations in the cytoplasm, nucleus and nucleolus of neurons. The cytoplasm contains on average 73% of the total iron, the nucleolus—although a hot spot for iron—due to its small volume only 6% of total iron. Additionally, the iron level in subcellular fractions were measured revealing that the microsome fraction, which usually contains holo-ferritin, has the highest iron content. We also present an estimate of the cellular ferritin concentration calculating 133pm 25 ferritin molecules per upmu hbox {m} in rat neurons.ConclusionGlial cells are the most iron-rich cells in the brain. Imbalances in iron homeostasis that lead to neurodegeneration may not only be originate from neurons but also from glial cells. It is feasible to estimate the ferritin concentration based on measured iron concentrations and a reasonable assumptions on iron load in the brain.

Structural optimization and quantum size effect of Si-nanocrystals in SiC interlayer fabricated with bio-template

Amorphous SiC/Si multilayers were fabricated using alternately magnetron sputtering of SiC and electron beam evaporation of Si targets. The as-deposited films were annealed at different temperatures from 800 till 1000 °C to form Si-nanocrystals (Si-NCs) and study the layered structural stability by different analytical techniques, including x-ray reflectivity (XRR), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and surface morphology by atomic force microscopy (AFM). XRR demonstrated that SiC/Si multilayers annealed at temperatures up to 1000 °C retain their layered structure. XRD and TEM confirmed the formation of Si-NCs after annealing at ≥800 °C. The Si-NCs size estimated from the TEM images is ∼4 nm for the multilayered sample with alternating 2 nm SiC and 4 nm Si layers. SIMS revealed that SiC/Si multilayers annealed at 800 °C possess the best periodic structure possibly due to the lowest carbon interdiffusion as compared to the samples annealed at higher temperatures. AFM micrograph confirmed that SiC/Si multilayers annealed at 800 °C characterized by the lowest surface roughness having RMS value of 0.123 nm as compared to the samples annealed at 900 °C and 1000 °C having RMS values of 0.207 and 0.530 nm, respectively. Size-controlled 3D array of Si-NCs separated by SiC barriers was fabricated by neutral beam etching of annealed SiC/Si multilayers with different Si layers thickness from 2 to 6 nm using a bio-template consisting of ferritin molecules. The size-dependent band gap energy of Si-NCs was estimated by optical spectroscopy to vary from 1.61 till 1.92 eV owing to the quantum confinement effect as the Si-NCs size decreases, which is appropriate for application in Si-based tandem solar cells.

The first crystal structure of crustacean ferritin that is a hybrid type of H and L ferritin.

Ferritin, a ubiquitous iron storage protein, has a crucial role in innate immunity in arthropods, which have no adaptive immune system. Arthropods are thought to have two types of ferritin molecules: the secreted type and the cytosolic type. Here, we present the first crystal structure of ferritin from crustacean, kuruma prawn (Marsupenaeus japonicus), at 1.16 Å resolution. This shrimp ferritin (MjFer) is the cytosolic type, and its structure shows well-conserved ferritin fold composed of a 4-helix bundle that assembles into a cage-like 24-mer. The structure of MjFer was more similar to those of human and vertebrate ferritins than to that of the secreted-type arthropod ferritin from an insect. MjFer possesses both a ferroxidase site and a nucleation site, which are the main characteristics of vertebrate H and L chain ferritins, respectively. The first crystal structure of crustacean ferritin, MjFer, has exceptionally high quality that provides the detailed structural information of metal moving pathway in ferritin.