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

Unveiling the stochastic nature of human heteropolymer ferritin self-assembly mechanism

Despite ferritin's critical role in regulating cellular and systemic iron levels, our understanding of the structure and assembly mechanism of isoferritins, discovered over eight decades ago, remains limited. Unveiling how the composition and molecular architecture of hetero-oligomeric ferritins confer distinct functionality to isoferritins is essential to understanding how the structural intricacies of H and L subunits influence their interactions with cellular machinery. In this study, ferritin heteropolymers with specific H to L subunit ratios were synthesized using a uniquely engineered plasmid design, followed by high-resolution cryo-electron microscopy analysis and deep learning-based amino acid modeling. Our structural examination revealed unique architectural features during the self-assembly mechanism of heteropolymer ferritins and demonstrated a significant preference for H-L heterodimer formation over H-H or L-L homodimers. Unexpectedly, while dimers seem essential building blocks in the protein self-assembly process, the overall mechanism of ferritin self-assembly is observed to proceed randomly through diverse pathways. The physiological significance of these findings is discussed including how ferritin microheterogeneity could represent a tissue-specific adaptation process that imparts distinctive tissue-specific functions to isoferritins.

Novel engineered HER2 specific recombinant protein nanocages for targeted drug delivery

Protein nanocages resemble natural biomimetic carriers and can be engineered to act as targeted delivery systems, making them an attractive option for various drug delivery and biomedical applications. Our research investigated the genetic link of a specific anti-HER2 peptide (LTVSPWY) to the exposed N-terminal region of the maize (Zea mays) ferritin 1 (ZmFer1) protein nanocage, employing either a 7-amino acid (for LTVS-ZmFer1) or 16-amino acid (for LTVS-L-ZmFer1) linker. We utilized a heat treatment method to load the chemotherapeutic drug doxorubicin into the protein nanocage. The construct with the longer linker (LTVS-L) produced a greater amount of soluble protein nanocage and was selected for further experiments. The average size, polydispersity index, and zeta potential of the engineered protein nanocage were 19.01 nm, 0.168, and - 2.13 mV, respectively. The LTVS-L-ZmFer1 protein nanocage exhibited excellent thermal stability, withstanding temperatures up to 100 °C with only partial denaturation. Furthermore, we observed that cellular uptake of the LTVS-L-ZmFer1 protein nanocages in HER2-positive breast cancer cells was significantly higher compared to ZmFer1 after labeling with FITC (fluorescein isothiocyanate) (P-value = 0.0001). In addition, we observed a significant decrease in the viability of SKBR3 cells when treated with DOX-loaded LTVS-L-ZmFer1 protein nanocages compared to cells treated with DOX-loaded ZmFer1 protein nanocages. Therefore, this new treatment strategy may prove to be an effective way to reduce both the side effects and toxicity associated with conventional cancer treatments in patients with HER2-positive breast cancer.

Designing Multifunctional Biomaterials via Protein Self-Assembly

Protein self-assembly is a fundamental biological process where proteins spontaneously organize into complex and functional structures without external direction. This process is crucial for the formation of various biological functionalities. However, when protein self-assembly fails, it can trigger the development of multiple disorders, thus making understanding this phenomenon extremely important. Up until recently, protein self-assembly has been solely linked either to biological function or malfunction; however, in the past decade or two it has also been found to hold promising potential as an alternative route for fabricating materials for biomedical applications. It is therefore necessary and timely to summarize the key aspects of protein self-assembly: how the protein structure and self-assembly conditions (chemical environments, kinetics, and the physicochemical characteristics of protein complexes) can be utilized to design biomaterials. This minireview focuses on the basic concepts of forming supramolecular structures, and the existing routes for modifications. We then compare the applicability of different approaches, including compartmentalization and self-assembly monitoring. Finally, based on the cutting-edge progress made during the last years, we summarize the current knowledge about tailoring a final function by introducing changes in self-assembly and link it to biomaterials' performance.

Programming interchangeable and reversible heterooligomeric protein self-assembly using a bifunctional ligand

Protein design for self-assembly allows us to explore the emergence of protein-protein interfaces through various chemical interactions. Heterooligomers, unlike homooligomers, inherently offer a comprehensive range of structural and functional variations. Besides, the macromolecular repertoire and their applications would significantly expand if protein components could be easily interchangeable. This study demonstrates that a rationally designed bifunctional linker containing an enzyme inhibitor and maleimide can guide the formation of diverse protein heterooligomers in an easily applicable and exchangeable manner without extensive sequence optimizations. As proof of concept, we selected four structurally and functionally unrelated proteins, carbonic anhydrase, aldolase, acetyltransferase, and encapsulin, as building block proteins. The combinations of two proteins with the bifunctional linker yielded four two-component heterooligomers with discrete sizes, shapes, and enzyme activities. Besides, the overall size and formation kinetics of the heterooligomers alter upon adding metal chelators, acidic buffer components, and reducing agents, showing the reversibility and tunability in the protein self-assembly. Given that the functional groups of both the linker and protein components are readily interchangeable, our work broadens the scope of protein-assembled architectures and their potential applications as functional biomaterials.

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

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.

Shape-Anisotropic Assembly of Protein Nanocages with Identical Building Blocks by Designed Intermolecular π-π Interactions

Protein lattices that shift the structure and shape anisotropy in response to environmental cues are closely coupled to potential functionality. However, to design and construct shape-anisotropic protein arrays from the same building blocks in response to different external stimuli remains challenging. Here, by a combination of the multiple, symmetric interaction sites on the outer surface of protein nanocages and the tunable features of phenylalanine-phenylalanine interactions, a protein engineering approach is reported to construct a variety of superstructures with shape anisotropy, including 3D cubic, 2D hexagonal layered, and 1D rod-like crystalline protein nanocage arrays by using one single protein building block. Notably, the assembly of these crystalline protein arrays is reversible, which can be tuned by external stimuli (pH and ionic strength). The anisotropic morphologies of the fabricated macroscopic crystals can be correlated with the Å-to-nm scale protein arrangement details by crystallographic elucidation. These results enhance the understanding of the freedom offered by an object's symmetry and inter-object π-π stacking interactions for protein building blocks to assemble into direction- and shape-anisotropic biomaterials.

Protein-based delivery systems for RNA delivery

RNA-based therapeutics have emerged as promising approaches to modulate gene expression and generate therapeutic proteins or antigens capable of inducing immune responses to treat a variety of diseases, such as infectious diseases, cancers, immunologic disorders, and genetic disorders. However, the efficient delivery of RNA molecules into cells poses significant challenges due to their large molecular weight, negative charge, and susceptibility to degradation by RNase enzymes. To overcome these obstacles, viral and non-viral vectors have been developed, including lipid nanoparticles, viral vectors, proteins, dendritic macromolecules, among others. Among these carriers, protein-based delivery systems have garnered considerable attention due to their potential to address specific issues associated with nanoparticle-based systems, such as liver accumulation and immunogenicity. This review provides an overview of currently marketed RNA drugs, underscores the significance of RNA delivery vector development, delineates the essential characteristics of an ideal RNA delivery vector, and introduces existing protein carriers for RNA delivery. By offering valuable insights, this review aims to serve as a reference for the future development of protein-based delivery vectors for RNA therapeutics.

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.

Self-Assembly of Platelet Lysates Proteins into Microparticles by Unnatural Disulfide Bonds for Bottom-Up Tissue Engineering

There is a demand to design microparticles holding surface topography while presenting inherent bioactive cues for applications in the biomedical and biotechnological fields. Using the pool of proteins present in human-derived platelet lysates (PLs), the production of protein-based microparticles via a simple and cost-effective method is reported, exploring the prone redox behavior of cysteine (Cy-SH) amino acid residues. The forced formation of new intermolecular disulfide bonds results in the precipitation of the proteins as spherical, pompom-like microparticles with adjustable sizes (15-50 µm in diameter) and surface topography consisting of grooves and ridges. These PL microparticles exhibit extraordinary cytocompatibility, allowing cell-guided microaggregates to form, while also working as injectable systems for cell support. Early studies also suggest that the surface topography provided by these PL microparticles can support osteogenic behavior. Consequently, these PL microparticles may find use to create live tissues via bottom-up procedures or injectable tissue-defect fillers, particularly for bone regeneration, with the prospect of working under xeno-free conditions.

Dual-targeted delivery of paclitaxel and indocyanine green with aptamer-modified ferritin for synergetic chemo-phototherapy

The combination of phototherapy and chemotherapy has become attractive and effective cancer treatment. However, the accurate delivery of both chemo-phototherapy drugs to the target site as well as the development of high-efficient phototherapy and chemotherapy drugs remain major challenges. In this study, indocyanine green (ICG) and paclitaxel (PTX)-loaded aptamer ferritin (HAS1411-PTX-ICG) was developed as a biocompatible nanoplatform for combined chemo/photothermal/photodynamic (PTT/PDT) therapy that was safe and highly effective against tumors. HAS1411 was prepared by coupling aptamer AS1411 to the surface of human H chain ferritin (HFtn) by the carbon diimide method to further enhance the targeting of HFtn. Both ICG and PTX were effectively encapsulated in the HAS1411 by incubation at 60 ℃. Moreover, under near-infrared (NIR) light irradiation, HAS1411 enhanced the photothermal effect and cell internalization of ICG, as well as the production of reactive oxygen species in cancer cells. HAS1411-PTX-ICG displayed effective cytotoxicity and a significant tumor spheroids inhibitory effect owning to the improved internalization of PTX and ICG mediated by TfR1 and nucleolin dual receptors. Co-loaded PTX combined with ICG can produce chemo/PTT/PDT under near-infrared (NIR) light irradiation, enhancing the anti-tumor effect. The dual-targeting HAS1411 nanocarrier developed in this study can be a promising delivery system for cancer therapy and the fabricated HAS1411-PTX-ICG possesses potential application in chemo-phototherapy.

Protein Nanotubes Assembled from Imidazole-Grafted Horseradish Peroxidase Nanogels

Protein assembly, a common phenomenon in nature, plays an important role in the evolution of life. Inspired by nature, assembling protein monomers into delicate nanostructures has emerged as an attractive research area. However, sophisticated protein assemblies usually need complicated designs or templates. In this work, we successfully fabricated protein nanotubes in a facile way by coordination interactions between imidazole-grafted horseradish peroxidase (HRP) nanogels (iHNs) and Cu2+. The iHNs were synthesized by polymerization on the surface of HRP by employing vinyl imidazole as a comonomer. By direct addition of Cu2+ into iHN solution, protein tubes were therefore formed. The size of the protein tubes could be adjusted by changing the added Cu2+ amount, and the mechanism behind the formation of protein nanotubes was elucidated. Furthermore, a highly sensitive H2O2 detection system was established based on the protein tubes. This work provides a facile method to construct diverse sophisticated functional protein nanomaterials.

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.

Molecular Engineering of E. coli Bacterioferritin: A Versatile Nanodimensional Protein Cage

Currently, intense interest is focused on the discovery and application of new multisubunit cage proteins and spherical virus capsids to the fields of bionanotechnology, drug delivery, and diagnostic imaging as their internal cavities can serve as hosts for fluorophores or bioactive molecular cargo. Bacterioferritin is unusual in the ferritin protein superfamily of iron-storage cage proteins in that it contains twelve heme cofactors and is homomeric. The goal of the present study is to expand the capabilities of ferritins by developing new approaches to molecular cargo encapsulation employing bacterioferritin. Two strategies were explored to control the encapsulation of a diverse range of molecular guests compared to random entrapment, a predominant strategy employed in this area. The first was the inclusion of histidine-tag peptide fusion sequences within the internal cavity of bacterioferritin. This approach allowed for the successful and controlled encapsulation of a fluorescent dye, a protein (fluorescently labeled streptavidin), or a 5 nm gold nanoparticle. The second strategy, termed the heme-dependent cassette strategy, involved the substitution of the native heme with heme analogs attached to (i) fluorescent dyes or (ii) nickel-nitrilotriacetate (NTA) groups (which allowed for controllable encapsulation of a histidine-tagged green fluorescent protein). An in silico docking approach identified several small molecules able to replace the heme and capable of controlling the quaternary structure of the protein. A transglutaminase-based chemoenzymatic approach to surface modification of this cage protein was also accomplished, allowing for future nanoparticle targeting. This research presents novel strategies to control a diverse set of molecular encapsulations and adds a further level of sophistication to internal protein cavity engineering.

Advances in Peptide-Based Hydrogel for Tissue Engineering

The development of peptide-based materials has emerged as one of the most challenging aspects of biomaterials in recent years. It has been widely acknowledged that peptide-based materials can be used in a broad range of biomedical applications, particularly in tissue engineering. Among them, hydrogels have been attracting considerable interest in tissue engineering because they mimic tissue formation conditions by providing a three-dimensional environment and a high water content. It has been found that peptide-based hydrogels have received more attention due to mimicking proteins, particularly extracellular matrix proteins, as well as the wide variety of applications they are capable of serving. It is without a doubt that peptide-based hydrogels have become the leading biomaterials of today owing to their tunable mechanical stability, high water content, and high biocompatibility. Here, we discuss in detail various types of peptide-based materials, emphasizing peptide-based hydrogels, and then we examine in detail how hydrogels are formed, paying particular attention to the peptide structures that are incorporated into the final structure. Following that, we discuss the self-assembly and formation of hydrogels under various conditions, as well as the parameters to be considered as critical factors, which include pH, amino acid composi- tion within the sequence, and cross-linking techniques. Further, recent studies on the development of peptide-based hydrogels and their applications in tissue engineering are reviewed.

Design, synthesis, and biological evaluation of 4-(1H-1,2,3-triazol-1-yl)benzamides as HSP90 inhibitors

Heat shock protein 90 (HSP90) is a promising anticancer drug target, which could be employed to construct HSP90 inhibitors-based drug conjugates for selective tumor therapy. Herein, a series of 4-(1H-1,2,3-triazol-1-yl)benzamides were rationally designed, synthesized as HSP90 inhibitors, and their structures were characterized by ¹H NMR, ¹³C NMR, and HR-MS. Preliminary HSP90 binding assay showed that compounds 6b, 6l, 6m, 6n, 6t, and 6u exhibited significant HSP90α binding affinity. Among these selected compounds, 6u displayed the most potent anti-proliferative activities and particularly in Capan-1 cell line. Molecular modeling studies also confirmed possible mode of interaction between 6u and the binding sites of HSP90 by hydrogen bond and hydrophobic interactions. Above all, these encouraging data indicated that 6u could be used as a HSP90 inhibitor for further study and helped the recognition of the 4-(1H-1,2,3-triazol-1-yl)benzamide motif as a new scaffold for HSP90 inhibitors.

Protein-based nanocages for vaccine development

Protein nanocages have attracted considerable attention in various fields of nanomedicine due to their intrinsic properties, including biocompatibility, biodegradability, high structural stability, and ease of modification of their surfaces and inner cavities. In vaccine development, these protein nanocages are suited for efficient targeting to and retention in the lymph nodes and can enhance immunogenicity through various mechanisms, including excellent uptake by antigen-presenting cells and crosslinking with multiple B cell receptors. This review highlights the superiority of protein nanocages as antigen delivery carriers based on their physiological and immunological properties such as biodistribution, immunogenicity, stability, and multifunctionality. With a focus on design, we discuss the utilization and efficacy of protein nanocages such as virus-like particles, caged proteins, and artificial caged proteins against cancer and infectious diseases such as coronavirus disease 2019 (COVID-19). In addition, we summarize available knowledge on the protein nanocages that are currently used in clinical trials and provide a general outlook on conventional distribution techniques and hurdles faced, particularly for therapeutic cancer vaccines.

Bio-inspired engineered ferritin-albumin nanocomplexes for targeted ferroptosis therapy

Nanotechnology-enabled ferroptosis therapy is an emerging paradigm for tumor treatment, but amplifying ferroptotic damage in tumor cells in a safe and selective manner is still challenging, which severely hinders its clinical translation. In this study, we constructed a bio-inspired protein nanocomplex based on natural-occurring bovine serum albumin (BSA) and ferritin for efficient tumor elimination via cooperatively enhanced ferroptosis therapy. The long-circulating BSA molecules provided multiple anchoring points for the efficient loading of the GPX4-inhibiting ferroptosis inducer (1S, 3R) RAS-selective lethal 3 (RSL3), which was further complexed with ferritin via acidity-responsive glutaraldehyde linkers. The ferritin moieties may not only bind to transferrin receptor 1 overexpressed on tumor cell membrane for targeted endocytic uptake but also be degraded in lysosomes to induce iron overload, which could substantially promote the lipid peroxidation in tumor cells and cooperate with the glutathione peroxidase 4 (GPX4)-inhibiting capability of RSL3 to induce pronounced ferroptosis. The in vitro and in vivo results collectively demonstrated that the albumin-ferritin-based nanocomplex could present superior antitumor effects with no obvious adverse effects, which may open new avenues for the clinical translation of ferroptosis-dependent therapeutic modalities.

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.

Research Advances of Lactoferrin in Electrostatic Spinning, Nano Self-Assembly, and Immune and Gut Microbiota Regulation

Lactoferrin (LF) is a naturally present iron-binding globulin with the structural properties of an N-lobe strongly positively charged terminus and a cage-like structure of nano self-assembly encapsulation. These unique structural properties give it potential for development in the fields of electrostatic spinning, targeted delivery systems, and the gut-brain axis. This review will provide an overview of LF's unique structure, encapsulation, and targeted transport capabilities, as well as its applications in immunity and gut microbiota regulation. First, the microstructure of LF is summarized and compared with its homologous ferritin, revealing both structural and functional similarities and differences between them. Second, the electrostatic interactions of LF and its application in electrostatic spinning are summarized. Its positive charge properties can be applied to functional environmental protection packaging materials and to improving drug stability and antiviral effects, while electrostatic spinning can promote bone regeneration and anti-inflammatory effects. Then the nano self-assembly behavior of LF is exploited as a cage-like protein to encapsulate bioactive substances to construct functional targeted delivery systems for applications such as contrast agents, antibacterial dressings, anti-cancer therapy, and gene delivery. In addition, some covalent and noncovalent interactions of LF in the Maillard reaction and protein interactions and other topics are briefly discussed. Finally, LF may affect immunological function via controlling the gut microbiota. In conclusion, this paper reviews the research advances of LF in electrostatic spinning, nano self-assembly, and immune and gut microbiota regulation, aiming to provide a reference for its application in the food and pharmaceutical fields.

Metallopolymer Particle Engineering via Etching of Boronate Polymers toward High-Performance Overall Water Splitting Catalysts

Metallopolymers combine the property features of both metallic compounds and organic polymers, representing a typical direction for the design of high-performance hybrid materials. Here, a highly adaptive etching method to create pores and cavities in the metallopolymer particles is established. Starting from boronate polymer (BP) and inorganic@BP core-shell particles, porous, hollow, and yolk-shell metallopolymer particles can be fabricated, respectively. By taking advantage of the easy control over composition and pore/cavity structure, these metallopolymer particles provide a universal platform for the fabrication of nitrogen, boron co-doped carbon nanocomposites loaded with metals (M-NBCs). The as-prepared M-NBCs exhibit remarkable catalytic activities toward oxygen evolution reaction and hydrogen evolution reaction. An alkaline overall water splitting cell assembled by using M-NBCs as the anode and cathode can be driven by a single AAA battery. The proposed strategy for the construction of metallopolymer composites may enlighten for the design of complex hybrid nanomaterials.

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.

Designing Stacked Assembly of Type III Rubisco for CO2 Fixation with Higher Efficiency

The slow catalytic rate of the carboxylation enzyme d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a major barrier to increasing the rate of carbon assimilation from the atmosphere into the biosphere. It is of great importance to establish a method to improve the carboxylation efficiency of Rubisco. Inspired by the assembly of Rubisco in carboxysomes, herein, we presented a rational protein engineering approach for the construction of one-dimensional (1D) protein arrays of type III Rubisco through designed π-π stacking interactions by using crystal structural information as a guide. In aqueous solutions, the dimensions of these 1D protein arrays collectively span nearly the entire nano- and micrometer scale (200 nm to 5.0 μm) by adjusting protein and NaCl concentrations. As a result, the stacked Rubisco assemblies increase by 40% in the carboxylase activity, while their turnover number (k_cat) is around twofold larger than that of wild-type III Rubisco. Notably, upon heat treatment at temperature up to 75 °C for 30 min, most of the assembled nanostructures and the enzyme activity are retained. More importantly, the initial relative activity of stacked assemblies retained 91% after 10 cycles of reuse. This work provides a simple, effective solution for the improvement of the CO₂ carboxylation efficiency of Rubisco.

High Internal Phase Emulsions Stabilized with Polyphenol-Amyloid Fibril Supramolecules for Encapsulation and Protection of Lutein

High internal phase emulsions (HIPEs), also called highly concentrated emulsions with a minimal internal phase volume fraction of 74%, have been paid increasing attention in the development of functional foods due to their high potential in loading with large amounts of hydrophobic nutriceuticals. In the present study, HIPEs stabilized by polyphenol-amyloid supramolecular filaments were prepared for encapsulation of olive oil and loading with lutein. Binding and stacking of the green tea polyphenol epigallocatechin gallate (EGCG) on the surface of amyloid fibrils fabricated from hen egg lysozyme resulted in the hybrid supramolecules, which assembled to form hydrogels. The amyloid fibril clusters shrouded by EGCG were observed in the microstructure of the hydrogels characterized by atomic force microscopy (AFM). HIPEs stabilized by the EGCG-amyloid fibril supramolecules showed the typical microstructure of highly packed polyhedral geometric oil droplets. The gel strength of the HIPEs stabilized by the hybrid supramolecules was greater than that of HIPEs stabilized by pure amyloid fibrils. The droplet size of the HIPEs first decreased and then increased with the increase of EGCG contents in the hybrid supramolecules, which was consistent with the corresponding emulsion morphologies obtained from the images of confocal laser scanning microscopy (CLSM). Aggregation of the protein-based nanofibrils appeared in the continuous phase at higher EGCG contents. The droplet size of the HIPEs decreased with the increase of the amyloid fibril concentration, accompanied by more packed and homogenously dispersed lipid droplets, as shown in the CLSM images. A high loading content of lutein of up to 10 mg/mL in the prepared HIPEs was realized, and the stability of lutein against ultraviolet irradiation, heat, iron, and hydrogen peroxide was promoted significantly. In addition, encapsulation with the HIPEs prevented the oxidization of olive oil, and this effect was enhanced with the increase of the EGCG content in the hybrid supramolecules ranging from 0 to 0.25 wt %. The protection function of the HIPEs might be ascribed to the membrane of interfacial amyloid fibrils and the crowded oil droplet environment, both of which could shield the pro-oxidation factors.

Programmed hierarchical radial association of anisotropic foldamer assemblies

Herein, we report the first example of a programmed radial assembly of anisotropic microparticles derived from a helical foldamer with a C-terminal cysteine residue. Surface-exposed thiols played a crucial role in facilitating the interparticle hydrogen bonding to form higher-order structures in an aqueous solution.

Autonomous Reaction Network Exploration in Homogeneous and Heterogeneous Catalysis

Autonomous computations that rely on automated reaction network elucidation algorithms may pave the way to make computational catalysis on a par with experimental research in the field. Several advantages of this approach are key to catalysis: (i) automation allows one to consider orders of magnitude more structures in a systematic and open-ended fashion than what would be accessible by manual inspection. Eventually, full resolution in terms of structural varieties and conformations as well as with respect to the type and number of potentially important elementary reaction steps (including decomposition reactions that determine turnover numbers) may be achieved. (ii) Fast electronic structure methods with uncertainty quantification warrant high efficiency and reliability in order to not only deliver results quickly, but also to allow for predictive work. (iii) A high degree of autonomy reduces the amount of manual human work, processing errors, and human bias. Although being inherently unbiased, it is still steerable with respect to specific regions of an emerging network and with respect to the addition of new reactant species. This allows for a high fidelity of the formalization of some catalytic process and for surprising in silico discoveries. In this work, we first review the state of the art in computational catalysis to embed autonomous explorations into the general field from which it draws its ingredients. We then elaborate on the specific conceptual issues that arise in the context of autonomous computational procedures, some of which we discuss at an example catalytic system.

1D alignment of proteins and other nanoparticles by using reversible covalent bonds on cyclic peptide nanotubes

Peptide nanotubes deposit on mica surface can be used for the alignment of proteins thank to the use of dynamic covalent bonds that allow the incorporation of appropriate ligands on nanotube surface.

PM1-loaded recombinant human H-ferritin nanocages: A novel pH-responsive sensing platform for the identification of cancer cells

The aggregation-induced emission (AIE) material has been widely used in biological detection due to their unique property of fluorescing in aggregation state. However, the poor dispersion and biocompatibility limit its application in in vivo real-time imaging. Here, a novel strategy is designed to obtain pH-responsive AIE nanomaterials, working through 4-Undecoxy Tetraphenyl Ethylene Methacrylate (PM1) block, with excellent features (dispersion, biocompatibility, self-reconstruction and cancer specific recognition). The recombinant human H-ferritin (rHuHF) was used to prepare rHuHF-PM1 nanocomposites which effectively supported the dispersion and transfer of PM1 in the biological environment, even making it target tumor cells due to the overexpression of ferritin receptors on tumor cells. To simulate the changes of rHuHF in intracellular lysosomes, particle size and fluorescence of rHuHF-PM1 were analyzed, which reflected the loose structural changes of rHuHF nanocages in weak acid system that facilitated the degradation of macromolecular rHuHF in intracellular lysosomes and following release of PM1. The released PM1 molecules aggregated and emitted brilliant blue fluorescence. Several cell lines, Hela, HT-29, HepG2, L-O2 and HUVEC have all been sensitively detected and distinguished. Accordingly, this nanocage has a potential to be applied to disease diagnosis and provides a novel sensing platform for the identification of cancer.

Protein-Based Nanoparticle Vaccines for SARS-CoV-2

The pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has upended healthcare systems and economies around the world. Rapid understanding of the structural biology and pathogenesis of SARS-CoV-2 has allowed the development of emergency use or FDA-approved vaccines and various candidate vaccines. Among the recently developed SARS-CoV-2 candidate vaccines, natural protein-based nanoparticles well suited for multivalent antigen presentation and enhanced immune stimulation to elicit potent humoral and cellular immune responses are currently being investigated. This mini-review presents recent innovations in protein-based nanoparticle vaccines against SARS-CoV-2. The design and strategy of displaying antigenic domains, including spike protein, receptor-binding domain (RBD), and other domains on the surface of various protein-based nanoparticles and the performance of the developed nanoparticle-based vaccines are highlighted. In the final part of this review, we summarize and discuss recent advances in clinical trials and provide an outlook on protein-based nanoparticle vaccines.

Apoferritin and Dps as drug delivery vehicles: Some selected examples in oncology

BACKGROUND

The ideal nanoparticle should be able to encapsulate either pharmaceutical agents or imaging probes so that it could treat or image clinical tumours by targeting the cancer site efficiently. Further, it would be an added advantage if it demonstrates: small size, built in targeting, biocompatibility and biodegradability. Ferritin, which is an endogenous self-assembling protein, stores iron and plays a role in iron homeostasis. When iron atoms are removed apoferritin (AFt) is formed which consists of a hollow shell where it can be used to load guest molecules. Due to its unique architecture, AFt has been investigated as a versatile carrier for tumour theranostic applications. DNA-binding protein from starved cells (Dps), which also belongs to the ferritin family, is a protein found only in prokaryotes. It is used to store iron and protect chromosomes from oxidative damage; because of its architecture, Dps could also be used as a delivery vehicle.

CONCLUSIONS

Both these nano particles are promising in the field of oncology, especially due to their stability, solubility and biocompatibility features. Further their exterior surface can be modified for better tumour-targeting ability. More studies, are warranted to determine the immunogenicity, biodistribution, and clearance from the body.

GENERAL PERSPECTIVE

This review discusses a few selected examples of the remarkable in vitro and in vivo studies that have been carried out in the recent past with the use of AFt and Dps in targeting and delivery of various pharmaceutical agents, natural products and imaging probes in the field of oncology.

Peptide Design and Self-assembly into Targeted Nanostructure and Functional Materials

Peptides have been extensively utilized to construct nanomaterials that display targeted structure through hierarchical assembly. The self-assembly of both rationally designed peptides derived from naturally occurring domains in proteins as well as intuitively or computationally designed peptides that form β-sheets and helical secondary structures have been widely successful in constructing nanoscale morphologies with well-defined 1-d, 2-d, and 3-d architectures. In this review, we discuss these successes of peptide self-assembly, especially in the context of designing hierarchical materials. In particular, we emphasize the differences in the level of peptide design as an indicator of complexity within the targeted self-assembled materials and highlight future avenues for scientific and technological advances in this field.

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Use of 3D domain swapping in constructing supramolecular metalloproteins

Supramolecules, which are formed by assembling multiple molecules by noncovalent intermolecular interactions instead of covalent bonds, often show additional properties that cannot be exhibited by a single molecule. Supramolecules have evolved into molecular machines in the field of chemistry, and various supramolecular proteins are responsible for life activities in the field of biology. The design and creation of supramolecular proteins will lead to development of new enzymes, functional biomaterials, drug delivery systems, etc.; thus, the number of studies on the regulation of supramolecular proteins is increasing year by year. Several methods, including disulfide bond, metal coordination, and surface-surface interaction, have been utilized to construct supramolecular proteins. In nature, proteins have been shown to form oligomers by 3D domain swapping (3D-DS), a phenomenon in which a structural region is exchanged between molecules of the same protein. We have been studying the mechanism of 3D-DS and utilizing 3D-DS to construct supramolecular metalloproteins. Cytochrome c forms cyclic oligomers and polymers by 3D-DS, whereas other metalloproteins, such as various c-type cytochromes and azurin form small oligomers and myoglobin forms a compact dimer. We have also utilized 3D-DS to construct heterodimers with different active sites, a protein nanocage encapsulating a Zn-SO₄ cluster in the internal cavity, and a tetrahedron with a designed building block protein. Protein oligomer formation was controlled for the 3D-DS dimer of a dimer-monomer transition protein. This article reviews our research on supramolecular metalloproteins.

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.

Organizing Multi-Enzyme Systems into Programmable Materials for Biocatalysis

Significant advances in enzyme discovery, protein and reaction engineering have transformed biocatalysis into a viable technology for the industrial scale manufacturing of chemicals. Multi-enzyme catalysis has emerged as a new frontier for the synthesis of complex chemicals. However, the in vitro operation of multiple enzymes simultaneously in one vessel poses challenges that require new strategies for increasing the operational performance of enzymatic cascade reactions. Chief among those strategies is enzyme co-immobilization. This review will explore how advances in synthetic biology and protein engineering have led to bioinspired co-localization strategies for the scaffolding and compartmentalization of enzymes. Emphasis will be placed on genetically encoded co-localization mechanisms as platforms for future autonomously self-organizing biocatalytic systems. Such genetically programmable systems could be produced by cell factories or emerging cell-free systems. Challenges and opportunities towards self-assembling, multifunctional biocatalytic materials will be discussed.