His-Mediated Reversible Self-Assembly of Ferritin Nanocages through Two Different Switches for Encapsulation of Cargo Molecules

Protein nanocages: A new frontier in mucosal vaccine delivery and immune activation

Mucosal infectious diseases represent a significant global health burden, impacting millions of people worldwide through pathogens that invade the respiratory, gastrointestinal, and urogenital tracts. Mucosal vaccines provide a promising strategy to combat these diseases by preventing pathogens from entering through the portals as well as within the systemic response compartment. However, challenges such as antigen instability, inefficient delivery, suboptimal immune activation, and the complex biology of mucosal barriers hinder their development. These limitations require integrating specialized adjuvants and delivery systems. Protein nanocages, self-assembling nanoscale structures that can be engineered, may provide an innovative solution for co-delivering antigens and adjuvants. With their remarkable stability, biocompatibility, and design versatility, protein nanocages can potentially overcome existing challenges in mucosal vaccine delivery and enhance protective immune responses. This review highlights the potential of protein nanocages to revolutionize mucosal vaccine development by addressing these challenges.

Enhancing Monodispersity and Thermal Stability of Human H-Ferritin as a Nanocarrier by Protein Design

Cage-like ferritin has been explored as a new class of nanovehicle in the field of food and nutrition, but its aggregation characteristics and low thermal stability limit its further application. This study focused on improving the monodispersity and thermal stability of recombinant human H-ferritin (rHuHF) for enhanced cargo molecule delivery. With the aid of AlphaFold 3.0, we designed a ferritin mutant by removing cysteine residues of rHuHF to improve monodispersity during storage while introducing histidine mutations at the C3 and C4 interfaces to enhance thermal stability. Notably, the designed protein structure was validated by a resolved crystal structure at the atomic level. As expected, the designed ferritin nanocage exhibited significantly improved monodispersity and thermal stability, enhancing its cargo loading capacity and cellular uptake efficiency. Such designed ferritin offers a more stable, efficient nanocarrier for cargo delivery and cargo protection under heat stress as compared to wild-type rHuHF.

Design and application of ferritin-based nanomedicine for targeted cancer therapy

Owing to its unique structure and favorable biocompatibility, ferritin has been widely studied as a promising drug carrier over the past two decades. Since the identification of its inherent tumor-targeting property due to unique recognition ablity of the transferrin receptor 1 (TfR1), ferritin-based nanomedicine has attracted widespread attention and triggered a research surge in the field of targeted cancer therapy. Along with progress in structure studies and modification technology, diverse strategies have been carried out to equip ferritin with on-demand functions, further improving the antitumor efficacy and in vivo safety of ferritin-based cancer therapy. In this review, we highlight the structure-based rational design of ferritin and summarize the design strategies in detail from two main perspectives: multifunctional modification and drug loading. In particular, the critical issues that need attention in the design are discussed in depth. Furthermore, we provide an overview of the latest advances in the application of ferritin-based nanomedicines in chemotherapy, phototherapy and immunotherapy, with particular emphasis on emerging therapeutic approaches among these therapies.

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.

Metals at the Helm: Revolutionizing Protein Assembly and Applications

Protein assembly is an essential process in biological systems, where proteins self-assemble into complex structures with diverse functions. Inspired by the exquisite control over protein assembly in nature, scientists have been exploring ways to design and assemble protein structures with precise control over their topologies and functions. One promising approach for achieving this goal is through metal coordination, which utilizes metal-binding motifs to mediate protein-protein interactions and assemble protein complexes with controlled stoichiometry and geometry. Metal coordination provides a modular and tunable approach for protein assembly and de novo structure design, where the metal ion acts as a molecular glue that holds the protein subunits together in a specific orientation. Metal-coordinated protein assemblies have shown great potential for developing functional metalloproteinase, novel biomaterials and integrated drug delivery systems. In this review, an overview of the recent advances in protein assemblies benefited from metal coordination is provided, focusing on various protein arrangements in different dimensions including protein oligomers, protein nanocage and higher-order protein architectures. Moreover, the key metal-binding motifs and strategies used to assemble protein structures with precise control over their properties are highlighted. The potential applications of metal-mediated protein assemblies in biotechnology and biomedicine are also discussed.

Food nanotechnology: opportunities and challenges

Food nanotechnology, which applies nanotechnology to food systems ranging from food production to food processing, packaging, and transportation, provides tremendous opportunities for conventional food science and industry innovation and improvement. Although great progress and rapid growth have been achieved in food nanotechnology research owing to the unique food features rendered by nanotechnology, at a fundamental level, food nanotechnology is still in its initial stages and the potential adverse effects of nanomaterials are still a controversial problem that attract public attention. Food-derived nanomaterials, compared to some inorganic nanoparticles and synthetic organic macromolecules, can be digested rapidly and produce similar digestion products to those produced normally, which become the mainstream and trend for food nanotechnology in practical applications, and are expected to be a vital tool for addressing the security problem and easing public concerns. These food-derived materials enable the favourable characteristics of nanostructures to be combined with the safety, biocompatibility, and bioactivity of natural food. Very recently, diverse food-derived nanomaterials have been explored and widely applied in multiple fields. Herein, we thoroughly summarize the fabrication and development of nanomaterials for use in food technology, as well as the recent advances in the improvement of food quality, revolutionizing food supply, and boosting food industries based on foodborne nanomaterials. The current challenges in food nanotechnology are also discussed. We hope this review can provide a detailed reference for experts and food manufacturers and inspire researchers to participate in the development of food nanotechnology for highly efficient food industry growth.

Ascorbyl palmitate nanofiber-reinforced hydrogels for drug delivery in soft issues

Nanofiber-based hydrogel delivery systems have recently shown great potential in biomedical applications, specifically due to their high surface-to-volume ratio of ultra-fine nanofibers and their ability to carry low solubility drugs. Herein, we introduce a visible light-triggered in situ-gelling drug vehicle (GAP Gel) composed of ascorbyl palmitate (AP) nanofibers and gelatin methacryloyl polymer. AP nanofibers form self-assembled structures through intermolecular interactions with a hydrophobic drug-loading core. We demonstrate that the hydrophilic periphery of AP nanofibers allows them to interact with other hydrophilic molecules via hydrogen bonds. The presence of AP nanofibers significantly enhances the viscoelasticity of GAP Gel in a concentration-dependent manner. Further, GAP Gel shows in vitro biocompatibility and sustained drug delivery efficacy when loaded with a hydrophobic antibiotic. Likewise, GAP Gel shows excellent in vivo biocompatibility when implanted in immunocompetent mice in various forms. Lastly, GAP Gels maintain cell viability when cultured in a 3D-environment over 7 days, establishing it as a promising and versatile hydrogel platform for the delivery of biotherapeutics.

A Versatile Virus-Mimetic Engineering Approach for Concurrent Protein Nanocage Surface-Functionalization and Cargo Encapsulation

Naturally occurring protein nanocages like ferritin are self-assembled from multiple subunits. Because of their unique cage-like structure and biocompatibility, there is a growing interest in their biomedical use. A multipurpose and straightforward engineering approach does not exist for using nanocages to make drug-delivery systems by encapsulating hydrophilic or hydrophobic drugs and developing vaccines by surface functionalization with a protein like an antigen. Here, a versatile engineering approach is described by mimicking the HIV-1 Gap polyprotein precursor. Various PREcursors of nanoCages (PREC) are designed and created by linking two ferritin subunits via a flexible linker peptide containing a protease cleavage site. These precursors can have additional proteins at their N-terminus, and their protease cleavage generates ferritin-like nanocages named protease-induced nanocages (PINCs). It is demonstrated that PINC formation allows concurrent surface decoration with a protein and hydrophilic or hydrophobic drug encapsulation up to fourfold more than the amount achieved using other methods. The PINCs/Drug complex is stable and efficiently kills cancer cells. This work provides insight into the precursors' design rules and the mechanism of PINCs formation. The engineering approach and mechanistic insight described here will facilitate nanocages' applications in drug delivery or as a platform for making multifunctional therapeutics like mosaic vaccines.

Ferritin nanocage-enabled detection of pathological tau in living human retinal cells

Tauopathies, including Alzheimer's disease and Frontotemporal Dementia, are debilitating neurodegenerative disorders marked by cognitive decline. Despite extensive research, achieving effective treatments and significant symptom management remains challenging. Accurate diagnosis is crucial for developing effective therapeutic strategies, with hyperphosphorylated protein units and tau oligomers serving as reliable biomarkers for these conditions. This study introduces a novel approach using nanotechnology to enhance the diagnostic process for tauopathies. We developed humanized ferritin nanocages, a novel nanoscale delivery system, designed to encapsulate and transport a tau-specific fluorophore, BT1, into human retinal cells for detecting neurofibrillary tangles in retinal tissue, a key marker of tauopathies. The delivery of BT1 into living cells was successfully achieved through these nanocages, demonstrating efficient encapsulation and delivery into retinal cells derived from human induced pluripotent stem cells. Our experiments confirmed the colocalization of BT1 with pathological forms of tau in living retinal cells, highlighting the method's potential in identifying tauopathies. Using ferritin nanocages for BT1 delivery represents a significant contribution to nanobiotechnology, particularly in neurodegenerative disease diagnostics. This method offers a promising tool for the early detection of tau tangles in retinal tissue, with significant implications for improving the diagnosis and management of tauopathies. This study exemplifies the integration of nanotechnology with biomedical science, expanding the frontiers of nanomedicine and diagnostic techniques.

Engineered protein cages with enhanced extracellular drug release for elevated antitumor efficacy

Human heavy chain ferritin (HFn) protein cage has been explored as a nanocarrier for targeted anticancer drug delivery. Here, we introduced a matrix metalloproteinases (MMPs)-cleavable sequence into the DE loop of HFn, creating an MMP-responsive variant, MR-HFn, for localized and extracellular drug release. The crystal structure of MR-HFn revealed that the addition of the MMPs recognition sequence did not affect the self-assembly of HFn but presented a surface-exposed loop susceptible to MMPs cleavage. Biochemical analysis indicated that this engineered protein cage is responsive to MMPs, enabling the targeted release of encapsulated drugs. To evaluate the therapeutic potential of this engineered protein cage, monosubstituted β-carboxy phthalocyanine zinc (CPZ), a type of photosensitizer, was loaded inside this protein cage. The prepared CPZ@MR-HFn showed higher uptake and stronger phototoxicity in MMPs overexpressed tumor cells, as well as enhanced penetration into multicellular tumor spheroids compared with its counterpart CPZ@HFn in vitro. In vivo, CPZ@MR-HFn displayed a higher tumor inhibitory rate than CPZ@HFn under illumination. These results indicated that MR-HFn is a promising nanocarrier for anticancer drug delivery and the MMP-responsive strategy here can also be adapted for other stimuli.

Advancements of the Molecular Directed Design and Structure-Activity Relationship of Ferritin Nanocage

Ferritin nanocages possess remarkable structural properties and biological functions, making them highly attractive for applications in functional materials and biomedicine. This comprehensive review presents an overview of the molecular characteristics, extraction and identification of ferritin, ferritin receptors, as well as the advancements in the directional design of high-order assemblies of ferritin and the applications based on its unique structural properties. Specifically, this Review focuses on the regulation of ferritin assembly from one to three dimensions, leveraging the symmetry of ferritin and modifications on key interfaces. Furthermore, it discusses targeted delivery of nutrition and drugs through facile loading and functional modification of ferritin. The aim of this Review is to inspire the design of micro/nano functional materials using ferritin and the development of nanodelivery vehicles for nutritional fortification and disease treatment.

Thermally Reversible Gel-Sol Transition of Hydrogels via Dissociation and Association of an Artificial Protein Nanocage

Oligomeric protein nanocages often disassemble into their subunits and reassemble by external stimuli. Thus, using these nanocages as cross-linkers for hydrogel network structures is a promising approach to allow hydrogels to undergo stimuli-responsive gel-sol transitions or self-healing. Here, we report hydrogels that show a reversible gel-sol transition resulting from the heat-induced dissociation and reassociation of protein nanocages. The hydrogel contained the 60-mer artificial protein nanocage, TIP60, as a supramolecular cross-linker for polyethylene glycol network structures. The hydrogel showed a gel-to-sol transition upon heating at a temperature above the melting point of TIP60 and immediately returned to a gel state upon cooling to room temperature. During the heating and cooling treatment of the hydrogel, small-angle X-ray scattering analysis suggested the dissociation and reassociation of TIP60. Furthermore, we demonstrated redox-responsive cargo release from TIP60 in the hydrogel. These results showed the potential of TIP60 as a component of multi-stimuli-responsive hydrogels.

Improvement of physicochemical properties of lycopene by the self-assembly encapsulation of recombinant ferritin GF1 from oyster (Crassostrea gigas)

BACKGROUND

Lycopene (LYC), a carotenoid found in abundance in ripe red fruits, exhibits higher singlet oxygen quenching activity than other carotenoids. However, the stability of LYC is extremely poor due to its high double-bond content. In this paper, a nano-encapsulation strategy based on highly stable marine-derived ferritin GF1 nanocages was used to improve the thermal stability and oxidation resistance of LYC, thereby boosting its functional effectiveness and industrial applicability.

RESULTS

The preparation of GF1-LYC nanoparticles benefited from the pH-responsive reversible self-assembly of GF1 to capture LYC molecules into GF1 cavities with a LYC-to-protein ratio of 51 to 1. After the encapsulation of the LYC, the reassembled GF1 nanocages maintained intact morphology and good monodispersity. The GF1-LYC nanoparticles incorporated the characteristic LYC peaks in spectrograms, and their powder form contained the crystalline form of LYC. Molecular docking revealed that LYC bound with the inner triple-axis channel areas of GF1, interacting with VAL139, LYS72, LYS65, TYR69, PHE129, HIS133, HIS62, and TYR134 amino acids through hydrophobic bonds. Fourier transform infrared spectroscopy also demonstrated the bonding of GF1 and LYC. In comparison with free LYC, GF1 reduced the thermal degradation of encapsulated LYC at 37 °C significantly and maintained the 2,2-Diphenyl-1-picrylhydrazyl (DPPH)-scavenging ability of LYC.

CONCLUSION

As expected, the water solubility, thermal stability, and antioxidant capacity of encapsulated LYC from GF1-LYC nanoparticles was notably improved in comparison with free LYC, indicating that the shell-like marine ferritin nanoplatform might enhance the stable delivery of LYC and promote its utilization in the field of food nutrition and in other industries. © 2023 Society of Chemical Industry.

A pH-Responsive Virus-Like Particle as a Protein Cage for a Targeted Delivery

A stimuli-responsive protein self-assembly offers promising utility as a protein nanocage for biotechnological and medical applications. Herein, the development of a virus-like particle (VLP) that undergoes a transition between assembly and disassembly under a neutral and acidic pH, respectively, for a targeted delivery is reported. The structure of the bacteriophage P22 coat protein is used for the computational design of coat subunits that self-assemble into a pH-responsive VLP. Subunit designs are generated through iterative computational cycles of histidine substitutions and evaluation of the interaction energies among the subunits under an acidic and neutral pH. The top subunit designs are tested and one that is assembled into a VLP showing the highest pH-dependent structural transition is selected. The cryo-EM structure of the VLP is determined, and the structural basis of a pH-triggered disassembly is delineated. The utility of the designed VLP is exemplified through the targeted delivery of a cytotoxic protein cargo into tumor cells in a pH-dependent manner. These results provide strategies for the development of self-assembling protein architectures with new functionality for diverse applications.

Assembly Requirements for the Construction of Large-Scale Binary Protein Structures

The precise assembly of multiple biomacromolecules into well-defined structures and materials is of great importance for various biomedical and nanobiotechnological applications. In this study, we investigate the assembly requirements for two-component materials using charged protein nanocages as building blocks. To achieve this, we designed several variants of ferritin nanocages to determine the surface characteristics necessary for the formation of large-scale binary three-dimensional (3D) assemblies. These nanocage variants were employed in protein crystallization experiments and macromolecular crystallography analyses, complemented by computational methods. Through the screening of nanocage variant combinations at various ionic strengths, we identified three essential features for successful assembly: (1) the presence of a favored crystal contact region, (2) the presence of a charged patch not involved in crystal contacts, and (3) sufficient distinctiveness between the nanocages. Surprisingly, the absence of noncrystal contact mediating patches had a detrimental effect on the assemblies, highlighting their unexpected importance. Intriguingly, we observed the formation of not only binary structures but also both negatively and positively charged unitary structures under previously exclusively binary conditions. Overall, our findings will inform future design strategies by providing some design rules, showcasing the utility of supercharging symmetric building blocks in facilitating the assembly of biomacromolecules into large-scale binary 3D assemblies.

Heat sensitive E-helix cut ferritin nanocages for facile and high-efficiency loading of doxorubicin

Ferritin possesses a stable and uniform cage structure, along with tumor-targeting properties and excellent biocompatibility, making it a promising drug delivery vehicle. However, the current ferritin drug loading strategy involves complex steps and harsh reaction conditions, resulting in low yield and recovery of drug loading, which limits the clinical application prospects of ferritin nanomedicine. In this study, we utilized the high-efficiency heat-sensitivity of the multiple channel switch structures of the E-helix-cut ferritin mutant (Ecut-HFn) and Cu2+ assistance to achieve high-efficiency loading of chemotherapeutic drugs in a one-step process at low temperatures. This method features mild reaction conditions (45 °C), high loading efficiency (about 110 doxorubicin (Dox) per Ecut-HFn), and improved protein and Dox recovery rates (with protein recovery rate around 94 % and Dox recovery rate reaching up to 45 %). The prepared ferritin-Dox particles (Ecut-HFn-Cu-Dox) exhibit a uniform size distribution, good stability, and retain the natural tumor targeting ability of ferritin. Overall, this temperature-controlled drug loading strategy utilizing heat-sensitivity ferritin mutants is energy-saving, environmentally friendly, efficient, and easy to operate, offering a new perspective for scaling up the industrial production of ferritin drug carriers.

Multifaceted Applications of Ferritin Nanocages in Delivering Metal Ions, Bioactive Compounds, and Enzymes: A Comprehensive Review

Ferritin, a distinctive iron-storage protein, possesses a unique cage-like nanoscale structure that enables it to encapsulate and deliver a wide range of biomolecules. Recent advances prove that ferritin can serve as an efficient 8 nm diameter carrier for various bioinorganic nutrients, such as minerals, bioactive polyphenols, and enzymes. This review offers a comprehensive summary of ferritin's structural features from different sources and emphasizes its functions in iron supplementation, calcium delivery, single- and coencapsulation of polyphenols, and enzyme package. Additionally, the influence of innovative food processing technologies, including manothermosonication, pulsed electric field, and atmospheric cold plasma, on the structure and function of ferritin are examined. Furthermore, the limitations and prospects of ferritin in food and nutritional applications are discussed. The exploration of ferritin as a multifunctional protein with the capacity to load various biomolecules is crucial to fully harnessing its potential in food applications.

Manufacturing of non-viral protein nanocages for biotechnological and biomedical applications

Protein nanocages are highly ordered nanometer scale architectures, which are typically formed by homo- or hetero-self-assembly of multiple monomers into symmetric structures of different size and shape. The intrinsic characteristics of protein nanocages make them very attractive and promising as a biological nanomaterial. These include, among others, a high surface/volume ratio, multi-functionality, ease to modify or manipulate genetically or chemically, high stability, mono-dispersity, and biocompatibility. Since the beginning of the investigation into protein nanocages, several applications were conceived in a variety of areas such as drug delivery, vaccine development, bioimaging, biomineralization, nanomaterial synthesis and biocatalysis. The ability to generate large amounts of pure and well-folded protein assemblies is one of the keys to transform nanocages into clinically valuable products and move biomedical applications forward. This calls for the development of more efficient biomanufacturing processes and for the setting up of analytical techniques adequate for the quality control and characterization of the biological function and structure of nanocages. This review concisely covers and overviews the progress made since the emergence of protein nanocages as a new, next-generation class of biologics. A brief outline of non-viral protein nanocages is followed by a presentation of their main applications in the areas of bioengineering, biotechnology, and biomedicine. Afterwards, we focus on a description of the current processes used in the manufacturing of protein nanocages with particular emphasis on the most relevant aspects of production and purification. The state-of-the-art on current characterization techniques is then described and future alternative or complementary approaches in development are also discussed. Finally, a critical analysis of the limitations and drawbacks of the current manufacturing strategies is presented, alongside with the identification of the major challenges and bottlenecks.

DNA-guided self-assembly in living cells

Self-assembly processes exist widely in life systems and play essential roles in maintaining life activities. It is promising to explore the molecular fundamentals and mechanisms of life systems through artificially constructing self-assembly systems in living cells. As an excellent self-assembly construction material, deoxyribonucleic acid (DNA) has been widely used to achieve the precise construction of self-assembly systems in living cells. This review focuses on the recent progress of DNA-guided intracellular self-assembly. First, the methods of intracellular DNA self-assembly based on the conformational transition of DNA are summarized, including complementary base pairing, the formation of G-quadruplex/i-motif, and the specific recognition of DNA aptamer. Next, The applications of DNA-guided intracellular self-assembly on the detection of intracellular biomolecules and the regulation of cell behaviors are introduced, and the molecular design of DNA in the self-assembly systems is discussed in detail. Ultimately, the challenges and opportunities of DNA-guided intracellular self-assembly are commented.

Ferritin nanocages: a versatile platform for nanozyme design

Nanozymes are a class of nanomaterials with enzyme-like activities and have attracted increasing attention due to their potential applications in biomedicine. However, nanozyme design incorporating the desired properties remains challenging. Natural or genetically engineered protein scaffolds, such as ferritin nanocages, have emerged as a promising platform for nanozyme design due to their unique protein structure, natural biomineralization capacity, self-assembly properties, and high biocompatibility. In this review, we highlight the intrinsic properties of ferritin nanocages, especially for nanozyme design. We also discuss the advantages of genetically engineered ferritin in the versatile design of nanozymes over natural ferritin. Additionally, we summarize the bioapplications of ferritin-based nanozymes based on their enzyme-mimicking activities. In this perspective, we mainly provide potential insights into the utilization of ferritin nanocages for nanozyme design.

LYC loaded ferritin nanoparticles for intracerebral delivery and the attenuation of neurodegeneration in D-gal-induced mice

Recombinant human H-ferritin nanocage (rHuHF) loaded with natural antioxidative lycopene molecules (LYC) was successfully constructed for the first time, aiming to enrich LYC in the brain and explore the regulation mechanism of this nanoparticles on neurodegeneration. Here, the mouse model was constructed via D-galactose-induced neurodegeneration based on behavioural analysis, histological observation, immunostaining analysis, Fourier transform infrared microscopy, and Western blotting analysis for the regulation of rHuHF-LYC. rHuHF-LYC improved the behaviour of mice in a dose-dependent manner. Besides, rHuHF-LYC can attenuate neuronal damage, maintain the number of Nissl body, increase the level of unsaturated fat, inhibit the activation of glial cells, and prevent excessive accumulation of neurotoxic proteins in the hippocampus of mice. More importantly, synaptic plasticity was activated in response to the regulation of rHuHF-LYC with excellent biocompatibility and biosafety. This study proved the validity of the direct use of natural antioxidant nano drugs for treating neurodegeneration, providing a promising therapeutic option against further imbalances in the degenerative brain microenvironment.

Ferritin nanocages as efficient nanocarriers and promising platforms for COVID-19 and other vaccines development

BACKGROUND

The development of safe and effective vaccines against SARS-CoV-2 and other viruses with high antigenic drift is of crucial importance to public health. Ferritin is a well characterized and ubiquitous iron storage protein that has emerged not only as a useful nanoreactor and nanocarrier, but more recently as an efficient platform for vaccine development.

SCOPE OF REVIEW

This review discusses ferritin structure-function properties, self-assembly, and novel bioengineering strategies such as interior cavity and exterior surface modifications for cargo encapsulation and delivery. It also discusses the use of ferritin as a scaffold for biomedical applications, especially for vaccine development against influenza, Epstein-Barr, HIV, hepatitis-C, Lyme disease, and respiratory viruses such as SARS-CoV-2. The use of ferritin for the synthesis of mosaic vaccines to deliver a cocktail of antigens that elicit broad immune protection against different viral variants is also explored.

MAJOR CONCLUSIONS

The remarkable stability, biocompatibility, surface functionalization, and self-assembly properties of ferritin nanoparticles make them very attractive platforms for a wide range of biomedical applications, including the development of vaccines. Strong immune responses have been observed in pre-clinical studies against a wide range of pathogens and have led to the exploration of ferritin nanoparticles-based vaccines in multiple phase I clinical trials.

GENERAL SIGNIFICANCE

The broad protective antibody response of ferritin nanoparticles-based vaccines demonstrates the usefulness of ferritin as a highly promising and effective approaches for vaccine development.

Ferritin-based nanomedicine for disease treatment

Ferritin is an endogenous protein which is self-assembled by 24 subunits into a highly uniform nanocage structure. Due to the drug-encapsulating ability in the hollow inner cavity and abundant modification sites on the outer surface, ferritin nanocage has been demonstrated great potential to become a multi-functional nanomedicine platform. Its good biocompatibility, low toxicity and immunogenicity, intrinsic tumor-targeting ability, high stability, low cost and massive production, together make ferritin nanocage stand out from other nanocarriers. In this review, we summarized ferritin-based nanomedicine in field of disease diagnosis, treatment and prevention. The different types of drugs to be loaded in ferritin, as well as drug-loading methods were classified. The strategies for site-specific and non-specific functional modification of ferritin were investigated, then the application of ferritin for disease imaging, drug delivery and vaccine development were discussed. Finally, the challenges restricting the clinical translation of ferritin-based nanomedicines were analyzed.

Reversible Assembly of an Artificial Protein Nanocage Using Alkaline Earth Metal Ions

Protein nanocages are of increasing interest for use as drug capsules, but the encapsulation and release of drug molecules at appropriate times require the reversible association and dissociation of the nanocages. One promising approach to addressing this challenge is the design of metal-dependent associating proteins. Such designed proteins typically have Cys or His residues at the protein surface for connecting the associating proteins through metal-ion coordination. However, Cys and His residues favor interactions with soft and borderline metal ions, such as Au⁺ and Zn²⁺, classified by the hard and soft acids and bases concept, restricting the types of metal ions available to drive association. Here, we show the alkaline earth (AE) metal-dependent association of the recently designed artificial protein nanocage TIP60, which is composed of 60-mer fusion proteins. The introduction of a Glu (hard base) mutation to the fusion protein (K67E mutant) prevented the formation of the 60-mer but formed the expected cage structure in the presence of Ca, Sr, or Ba ions (hard acids). Cryogenic electron microscopy (cryo-EM) analysis indicated a Ba ion at the interface of the subunits. Furthermore, we demonstrated the encapsulation and release of single-stranded DNA molecules using this system. Our results provide insights into the design of AE metal-dependent association and dissociation mechanisms for proteins.

Reassembly Design of Ferritin Cages

The ferritin family is distributed in nearly all organisms and protects them from iron-induced oxidative damage. Besides, its highly symmetrical structure and biochemical features make it an appealing material for biotechnological applications, such as building blocks for multidimensional assembly, templates for nano-reactors, and scaffolds for encapsulation and delivery of nutrients and drugs. Moreover, it is of great significance to construct ferritin variants with different properties, size, and shape to further broaden its application. In this chapter, we present a routine process of the ferritin redesign and the characterization method of the protein structure to provide a feasible scheme.

Spatiotemporal control over 3D protein nanocage superlattices for the hierarchical encapsulation and release of different cargo molecules

Taking inspiration from Nature, we have constructed a two-compartment system based on 3D ferritin nanocage superlattices, the self-assembly behavior of which can be spatiotemporally controlled using two designed switches. One pH switch regulates the assembly of the ferritin subunit into its shell-like structure, whereas the other metal switch is responsible for assembly of the 3D superlattices from ferritin nanocages as building blocks. Consequently, this system holds great promise for the hierarchical encapsulation and release of two different cargo molecules.

Ferritin nanocage based delivery vehicles: From single-, co- to compartmentalized- encapsulation of bioactive or nutraceutical compounds

Bioactive or nutraceutical ingredients have been widely used in pursuit of health and well-being. However, the environmental instability, poor solubility and bioavailability, and unspecific delivery highly limited their practical values. By virtue of the unique shell-like structure, definite disassembly/reassembly behavior, and excellent safety profile of ferritin protein, it stands out among of various nano-materials and is emerging as one of the most promising vehicles for the encapsulation and delivery of bioactive ingredients or drugs. In this review, we present a systematic overview of recent advances of ferritin-based delivery systems from single-encapsulation, co-encapsulation, to compartmentalized-encapsulation of bioactive ingredients or drugs. Different encapsulation strategies for cargo loading as well as their advantages and drawbacks have been critically reviewed. This study emphasized the importance of the construction of compartmentalized delivery systems through the usage of ferritin nanocages, which exhibit great potential for facilitating the synergistic functionality of different types of cargos. Lastly, the applications of ferritin nanocages for physicochemical improvements and functionality achievements of loaded cargos are summarized. In conclusion, ferritin protein nanocages not only are excellent nanocarriers, but also can act as"multi-seated" vehicles for co-encapsulation and compartmentalized encapsulation of different cargos simultaneously.

Application Perspectives of Nanomedicine in Cancer Treatment

Cancer is a disease that seriously threatens human health. Based on the improvement of traditional treatment methods and the development of new treatment modes, the pattern of cancer treatment is constantly being optimized. Nanomedicine plays an important role in these evolving tumor treatment modalities. In this article, we outline the applications of nanomedicine in three important tumor-related fields: chemotherapy, gene therapy, and immunotherapy. According to the current common problems, such as poor targeting of first-line chemotherapy drugs, easy destruction of nucleic acid drugs, and common immune-related adverse events in immunotherapy, we discuss how nanomedicine can be combined with these treatment modalities, provide typical examples, and summarize the advantages brought by the application of nanomedicine.

How Pore Architecture Regulates the Function of Nanoscale Protein Compartments

Self-assembling proteins can form porous compartments that adopt well-defined architectures at the nanoscale. In nature, protein compartments act as semipermeable barriers to enable spatial separation and organization of complex biochemical processes. The compartment pores play a key role in their overall function by selectively controlling the influx and efflux of important biomolecular species. By engineering the pores, the functionality of compartments can be tuned to facilitate non-native applications, such as artificial nanoreactors for catalysis. In this review, we analyze how protein structure determines the porosity and impacts the function of both native and engineered compartments, highlighting the wealth of structural data recently obtained by cryo-EM and X-ray crystallography. Through this analysis, we offer perspectives on how current structural insights can inform future studies into the design of artificial protein compartments as nanoreactors with tunable porosity and function.

Advances in Rational Protein Engineering toward Functional Architectures and Their Applications in Food Science

Protein biomolecules including enzymes, cagelike proteins, and specific peptides have been continuously exploited as functional biomaterials applied in catalysis, nutrient delivery, and food preservation in food-related areas. However, natural proteins usually function well in physiological conditions, not industrial conditions, or may possess undesirable physical and chemical properties. Currently, rational protein design as a valuable technology has attracted extensive attention for the rational engineering or fabrication of ideal protein biomaterials with novel properties and functionality. This article starts with the underlying knowledge of protein folding and assembly and is followed by the introduction of the principles and strategies for rational protein design. Basic strategies for rational protein engineering involving experienced protein tailoring, computational prediction, computation redesign, and de novo protein design are summarized. Then, we focus on the recent progress of rational protein engineering or design in the application of food science, and a comprehensive summary ranging from enzyme manufacturing to cagelike protein nanocarriers engineering and antimicrobial peptides preparation is given. Overall, this review highlights the importance of rational protein engineering in food biomaterial preparation which could be beneficial for food science.

Amelioration of acute myocardial infarction injury through targeted ferritin nanocages loaded with an ALKBH5 inhibitor

The roles of m⁶A RNA methylation and mitochondrial metabolism in acute myocardial infarction (AMI) remain unclear. In this study, we demonstrated that m⁶A RNA methylation affected ischemia/reperfusion (I/R) injury in AMI through the "Erasers" protein ALKBH5-related metabolic reprogramming, characterized by the inhibition of enzyme activities of the tricarboxylic acid cycle; moreover, a surface-modified bioengineered ferritin nanocage was obtained from Archaeoglobus fulgidus, with a chimeric structure containing 8 lysine residues, SpyTag/SpyCatcher, and the C1q ligand Scarf1, which could disassemble and self-assemble in neutral solutions according to different Mg²⁺ concentrations. The surface-modified bioengineered ferritin nanocage targeted the dying cells in the infarct area under the guidance of Scarf1. These cells were then phagocytosed through recognition of their TfR1 receptor. Lysosomal escape was achieved through the 8 lysine residues on the nanocage, and the nanocage disassembled based on the differences in intracellular and extracellular Mg²⁺ concentrations. Finally, the ALKBH5 inhibitor IOX1 was loaded onto the ferritin nanocage and used in the AMI model, and it was found to effectively improve cardiac function. These results provide a potential strategy for the treatment of AMI in the future. STATEMENT OF SIGNIFICANCE: In acute myocardial infarction (AMI) induced by ischemia/reperfusion injury, m⁶A RNA methylation aggravates the injury through the "Erasers" protein ALKBH5-related metabolic reprogramming. To achieve precise treatment, genetic engineering-based recombinant expression technology was used to obtain a ferritin from Archaeoglobus fulgidus. The obtained ferritin was designated as HAfFtO, and it can disassemble and self-assemble in a neutral solution under different Mg²⁺ concentrations and achieve lysosomal escape. Three G4S linkers were used to connect SpyTag with HAfFtO to synthesize HAfFtO-ST and recombination Scarf1 containing SpyCatcher structure, namely SC-Sf. According to the SpyTag/SpyCatcher technique, HAfFtO-ST and SC-Sf can form a gentle and firm combination, namely HSSS. The ALKBH5 inhibitor IOX1 was loaded on HSSS to form HSSS-I. HSSS-I effectively improved the cardiac function and decreased the infarct size in AMI.

Protein nanoparticles directed cancer imaging and therapy

Cancer has been a serious threat to human health. Among drug delivery carriers, protein nanoparticles are unique because of their mild and environmentally friendly preparation methods. They also inherit desired characteristics from natural proteins, such as biocompatibility and biodegradability. Therefore, they have solved some problems inherent to inorganic nanocarriers such as poor biocompatibility. Also, the surface groups and cavity of protein nanoparticles allow for easy surface modification and drug loading. Besides, protein nanoparticles can be combined with inorganic nanoparticles or contrast agents to form multifunctional theranostic platforms. This review introduces representative protein nanoparticles applicable in cancer theranostics, including virus-like particles, albumin nanoparticles, silk protein nanoparticles, and ferritin nanoparticles. It also describes the common methods for preparing them. It then critically analyzes the use of a variety of protein nanoparticles in improved cancer imaging and therapy.

Artificial protein assemblies with well-defined supramolecular protein nanostructures

Nature uses a wide range of well-defined biomolecular assemblies in diverse cellular processes, where proteins are major building blocks for these supramolecular assemblies. Inspired by their natural counterparts, artificial protein-based assemblies have attracted strong interest as new bio-nanostructures, and strategies to construct ordered protein assemblies have been rapidly expanding. In this review, we provide an overview of very recent studies in the field of artificial protein assemblies, with the particular aim of introducing major assembly methods and unique features of these assemblies. Computational de novo designs were used to build various assemblies with artificial protein building blocks, which are unrelated to natural proteins. Small chemical ligands and metal ions have also been extensively used for strong and bio-orthogonal protein linking. Here, in addition to protein assemblies with well-defined sizes, protein oligomeric and array structures with rather undefined sizes (but with definite repeat protein assembly units) also will be discussed in the context of well-defined protein nanostructures. Lastly, we will introduce multiple examples showing how protein assemblies can be effectively used in various fields such as therapeutics and vaccine development. We believe that structures and functions of artificial protein assemblies will be continuously evolved, particularly according to specific application goals.

Protein-Based Nanoparticles for the Imaging and Treatment of Solid Tumors: The Case of Ferritin Nanocages, a Narrative Review

Protein nanocages have been studied extensively, due to their unique architecture, exceptional biocompatibility and highly customization capabilities. In particular, ferritin nanocages (FNs) have been employed for the delivery of a vast array of molecules, ranging from chemotherapeutics to imaging agents, among others. One of the main favorable characteristics of FNs is their intrinsic targeting efficiency toward the Transferrin Receptor 1, which is overexpressed in many tumors. Furthermore, genetic manipulation can be employed to introduce novel variants that are able to improve the loading capacity, targeting capabilities and bio-availability of this versatile drug delivery system. In this review, we discuss the main characteristics of FN and the most recent applications of this promising nanotechnology in the field of oncology with a particular emphasis on the imaging and treatment of solid tumors.

The Impact of Redox, Hydrolysis and Dehydration Chemistry on the Structural and Magnetic Properties of Magnetoferritin Prepared in Variable Thermal Conditions

Ferritin, a spherically shaped protein complex, is responsible for iron storage in bacteria, plants, animals, and humans. Various ferritin iron core compositions in organisms are associated with specific living requirements, health state, and different biochemical roles of ferritin isomers. Magnetoferritin, a synthetic ferritin derivative, serves as an artificial model system of unusual iron phase structures found in humans. We present the results of a complex structural study of magnetoferritins prepared by controlled in vitro synthesis. Using various complementary methods, it was observed that manipulation of the synthesis technology can improve the physicochemical parameters of the system, which is useful in applications. Thus, a higher synthesis temperature leads to an increase in magnetization due to the formation of the magnetite phase. An increase in the iron loading factor has a more pronounced impact on the protein shell structure in comparison with the pH of the aqueous medium. On the other hand, a higher loading factor at physiological temperature enhances the formation of an amorphous phase instead of magnetite crystallization. It was confirmed that the iron-overloading effect alone (observed during pathological events) cannot contribute to the formation of magnetite.

Bionanomaterials based on protein self-assembly: Design and applications in biotechnology

Elegant protein assembly to generate new biomaterials undergoes extremely rapid development for wide extension of biotechnology applications, which can be a powerful tool not only for creating nanomaterials but also for advancing understanding of the structure of life. Unique biological properties of proteins bestow these artificial biomaterials diverse functions that can permit them to be applied in encapsulation, bioimaging, biocatalysis, biosensors, photosynthetic apparatus, electron transport, magnetogenetic applications, vaccine development and antibodies design. This review gives a perspective view of the latest advances in the construction of protein-based nanomaterials. We initially start with distinguishable, specific interactions to construct sundry nanomaterials through protein self-assembly and concisely expound the assembly mechanism from the design strategy. And then, the design and construction of 0D, 1D, 2D, 3D protein assembled nanomaterials are especially highlighted. Furthermore, the potential applications have been discussed in detail. Overall, this review will illustrate how to fabricate highly sophisticated nanomaterials oriented toward applications in biotechnology based on the rules of supramolecular chemistry.

Ferritin: A Multifunctional Nanoplatform for Biological Detection, Imaging Diagnosis, and Drug Delivery

Ferritins are spherical iron storage proteins within cells that are composed of a combination of 24 subunits of two types, heavy-chain ferritin (HFn) and light-chain ferritin (LFn). They autoassemble naturally into a spherical hollow nanocage with an outer diameter of 12 nm and an interior cavity that is 8 nm in diameter. In recent years, with the constantly emerging safety issues and the concerns about unfavorable uniformity and indefinite in vivo behavior of traditional nanomedicines, the characteristics of native ferritin nanocages, such as the unique nanocage structure, excellent safety profile, and definite in vivo behavior, make ferritin-based formulations uniquely attractive for nanomedicine development. To date, a variety of cargo molecules, including therapeutic drugs (e.g., cisplatin, carboplatin, paclitaxel, curcumin, atropine, quercetin, gefitinib, daunomycin, epirubicin, doxorubicin, etc.), imaging agents (e.g., fluorescence dyes, radioisotopes, and MRI contrast agents), nucleic acids (e.g., siRNA and miRNA), and metal nanoparticles (e.g., Fe₃O₄, CeO₂, AuPd, CuS, CoPt, FeCo, Ag, etc.) have been loaded into the interior cavity of ferritin nanocages for a broad range of biomedical applications from in vitro biosensing to targeted delivery of cargo molecules in living systems with the aid of modified targeting ligands either genetically or chemically. We reported that human HFn could selectively deliver a large amount of cargo into tumors in vivo via transferrin receptor 1 (TfR1)-mediated tumor-cell-specific targeting followed by rapid internalization. By the use of the intrinsic tumor-targeting property and unique nanocage structure of human HFn, a broad variety of cargo-loaded HFn formulations have been developed for biological analysis, imaging diagnosis, and medicine development. In view of the intrinsic tumor-targeting property, unique nanocage structure, lack of immunogenicity, and definite in vivo behavior, human HFn holds promise to promote therapeutic drugs, diagnostic imaging agents, and targeting moieties into multifunctional nanomedicines.Since the report of the intrinsic tumor-targeting property of human HFn, we have extensively explored human HFn as an ideal nanocarrier for tumor-targeted delivery of anticancer drugs, MRI contrast agents, inorganic nanoparticles, and radioisotopes. In particular, by the use of genetic tools, we also have genetically engineered human HFn nanocages to recognize a broader range of disease biomarkers. In this Account, we systematically review human ferritins from characterizing their tumor-binding property and understanding their mechanism and kinetics for cargo loading to exploring their biomedical applications. We finally discuss the prospect of ferritin-based formulations to become next-generation nanomedicines. We expect that ferritin formulations with unique physicochemical characteristics and intrinsic tumor-targeting property will attract broad interest in fundamental drug research and offer new opportunities for nanomedicine development.

Ferritin nanocage: A promising and designable multi-module platform for constructing dynamic nanoassembly-based drug nanocarrier

Ferritin has been widely recognized as an ideal drug delivery vehicle owing to its unique cage-like structure. Coupled with intrinsic targeting ability and excellent biosafety, ferritin-based drug delivery system, recently coined as ferritin drug carrier (FDC), has sparked great interest among researchers and shown promising application potential in the biomedical field. However, the flexibility and accuracy of traditional FDCs are limited when facing with complex disease microenvironments. To meet the fast-growing requirements for precision medicine, ferritin can serve as a designable multi-module platform to fabricate smarter FDC, which we introduce here as dynamic nanoassembly-based ferritin drug carrier (DNFDC). Compared to conventional FDC, DNFDCs directly integrate required functions into their nanostructure, which can achieve dynamic transformation upon stimuli to specifically activate and exert therapeutic functions at targeted sites. In this review, we summarize the superior characteristics of ferritin that contribute to the on-demand design of DNFDC and outline the current advances in DNFDC. Moreover, the potential research directions and challenges are also discussed here. Hopefully, this review may inspire the future development of DNFDC.

Redesign of protein nanocages: the way from 0D, 1D, 2D to 3D assembly

Compartmentalization is a hallmark of living systems. Through compartmentalization, ubiquitous protein nanocages such as viral capsids, ferritin, small heat shock proteins, and DNA-binding proteins from starved cells fulfill a variety of functions, while their shell-like structures hold great promise for various applications in the field of nanomedicine and nanotechnology. However, the number and structure of natural protein nanocages are limited, and these natural protein nanocages may not be suited for a given application, which might impede their further application as nanovehicles, biotemplates or building blocks. To overcome these shortcomings, different strategies have been developed by scientists to construct artificial protein nanocages, and 1D, 2D and 3D protein arrays with protein nanocages as building blocks through genetic and chemical modification to rival the size and functionality of natural protein nanocages. This review outlines the recent advances in the field of the design and construction of artificial protein nanocages and their assemblies with higher order, summarizes the strategies for creating the assembly of protein nanocages from zero-dimension to three dimensions, and introduces their corresponding applications in the preparation of nanomaterials, electrochemistry, and drug delivery. The review will highlight the roles of both the inter-subunit/intermolecular interactions at the key interface and the protein symmetry in constructing and controlling protein nanocage assemblies with different dimensions.

Kinetics of Ferritin Self-Assembly by Laser Light Scattering: Impact of Subunit Concentration, pH, and Ionic Strength

Ferritins, the cellular iron repositories, are self-assembled, hollow spherical nanocage proteins composed of 24 subunits. The self-assembly process in ferritin generates the electrostatic gradient to rapidly sequester Fe(II) ions, thereby minimizing its toxicity (Fenton reaction). Although the factors that drive self-assembly and control its kinetics are little investigated, its inherent reversibility has been utilized for cellular imaging and targeted drug delivery. The current work tracks the kinetics of ferritin self-assembly by laser light scattering and investigates the factors that influence the process. The formation of partially structured subunit-monomers/dimers, at pH ≤ 1.5, serves as the starting material for the self-assembly, which upon increasing the pH exhibits biphasic behavior (a rapid assembly process coupled with subunit folding followed by a slower reassembly/reorganization process) and completes within 10 min. The ferritin self-assembly accelerated with subunit concentration and ionic strength (t_1/2 decreases in both the cases) but slowed down with the pH of the medium from 5.5 to 7.5 (t_1/2 increases). These findings would help to regulate the ferritin self-assembly to enhance the loading/unloading of drugs/nanomaterials for exploiting it as a nanocarrier and nanoreactor.