"Silent" Amino Acid Residues at Key Subunit Interfaces Regulate the Geometry of Protein Nanocages

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.

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.

A novel highly thermostable and stress resistant ROS scavenging metalloprotein from Paenibacillus

Reactive oxygen species (ROS) are unstable metabolites produced during cellular respiration that can cause extensive damage to the body. Here we report a unique structural metalloprotein called RSAPp for the first time, which exhibits robust ROS-scavenging activity, high thermostability, and stress resistance. RSAPp is a previously uncharacterized DUF2935 (domain of unknown function, accession number: cl12705) family protein from Paenibacillus, containing a highly conserved four-helix bundle with binding sites for variable-valence metal ions (Mn2+/Fe2+/Zn2+). Enzymatic characterization results indicated that RSAPp displays the functionality of three different antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In particular, RSAPp exhibits a significant SOD-like activity that is remarkably effective in eliminating superoxide radicals (up to kcat/KM = 2.27 × 1011 mol-1 s-1), and maintains the catalytical active in a wide range of temperatures (25-100 °C) and pH (pH 2.0-9.0), as well as resistant to high temperature, alkali and acidic pH, and 55 different concentrations of detergent agents, chemical solvents, and inhibitors. These properties make RSAPp an attractive candidate for various industrial applications, including cosmetics, food, and pharmaceuticals.

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.

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.

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.

Directed Self-Assembly of Dimeric Building Blocks into Networklike Protein Origami to Construct Hydrogels

Engineering proteins to construct self-assemblies is of crucial significance not only for understanding the sophisticated living systems but also for fabricating advanced materials with unexplored functions. However, due to the inherent chemical heterogeneity and structural complexity of the protein surface, designing complex protein assemblies in an anisotropic fashion remains challenging. Here, we describe a self-assembly approach to fabricating protein origami with a networklike structure by designing dual noncovalent interactions on the different positions of a single protein building block. With dimeric proteins as building blocks, 1D protein filaments were constructed by the designed metal coordination at key protein interfaces. Subsequently, the network superstructures were created by the cross-linking of the 1D protein filaments at branch point linkages through the second designed π-π stacking interactions. Notably, upon increasing the protein concentration, the formed protein networks convert into hydrogels with reversible, injectable, and self-healing properties, which have the ability to promote bone regeneration. This strategy could be used to fabricate other protein-based materials with unexplored functions.

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.

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.

Protein Assembly by Design

Proteins are nature's primary building blocks for the construction of sophisticated molecular machines and dynamic materials, ranging from protein complexes such as photosystem II and nitrogenase that drive biogeochemical cycles to cytoskeletal assemblies and muscle fibers for motion. Such natural systems have inspired extensive efforts in the rational design of artificial protein assemblies in the last two decades. As molecular building blocks, proteins are highly complex, in terms of both their three-dimensional structures and chemical compositions. To enable control over the self-assembly of such complex molecules, scientists have devised many creative strategies by combining tools and principles of experimental and computational biophysics, supramolecular chemistry, inorganic chemistry, materials science, and polymer chemistry, among others. Owing to these innovative strategies, what started as a purely structure-building exercise two decades ago has, in short order, led to artificial protein assemblies with unprecedented structures and functions and protein-based materials with unusual properties. Our goal in this review is to give an overview of this exciting and highly interdisciplinary area of research, first outlining the design strategies and tools that have been devised for controlling protein self-assembly, then describing the diverse structures of artificial protein assemblies, and finally highlighting the emergent properties and functions of these assemblies.

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.

Development of purification process for dual-function recombinant human heavy-chain ferritin by the investigation of genetic modification impact on conformation

Ferritin is a promising drug delivery platform and has been functionalized through genetic modifications. This work has designed and expressed a dual-functional engineered human heavy-chain ferritin (HFn) with the inserted functional peptide PAS and RGDK to extend half-life and improve tumor targeted drug delivery. A facile and cost-effective two-step purification pathway for recombinant HFn was developed. The genetic modification was found to affect HFn conformation, and therefore varied the purification performance. Heat-acid precipitation followed by butyl fast flow hydrophobic interaction chromatography (HIC) has been developed to purify HFn and modified HFns. Nucleic acid removal reached above 99.8% for HFn and modified HFns. However, HFn purity reached above 95% and recovery yield (overall) above 90%, compared with modified HFns purity above 82% and recovery yield (overall) above 58%. It is interesting to find that the inserted functional peptides significantly changed the molecule conformation, where a putative turnover of the E-helix with the inserted functional peptides formed a "flop" conformation, in contrast with the "flip" conformation of HFn. It could be the cause of fragile stability of modified HFns, and therefore less tolerant to heat and acid condition, observed by the lower recovery yield in heat-acid precipitation.

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.

Protein interface redesign facilitates the transformation of nanocage building blocks to 1D and 2D nanomaterials

Although various artificial protein nanoarchitectures have been constructed, controlling the transformation between different protein assemblies has largely been unexplored. Here, we describe an approach to realize the self-assembly transformation of dimeric building blocks by adjusting their geometric arrangement. Thermotoga maritima ferritin (TmFtn) naturally occurs as a dimer; twelve of these dimers interact with each other in a head-to-side manner to generate 24-meric hollow protein nanocage in the presence of Ca²⁺ or PEG. By tuning two contiguous dimeric proteins to interact in a fully or partially side-by-side fashion through protein interface redesign, we can render the self-assembly transformation of such dimeric building blocks from the protein nanocage to filament, nanorod and nanoribbon in response to multiple external stimuli. We show similar dimeric protein building blocks can generate three kinds of protein materials in a manner that highly resembles natural pentamer building blocks from viral capsids that form different protein assemblies.

Artificial Organelles: Towards Adding or Restoring Intracellular Activity

Compartmentalization is one of the main characteristics that define living systems. Creating a physically separated microenvironment allows nature a better control over biological processes, as is clearly specified by the role of organelles in living cells. Inspired by this phenomenon, researchers have developed a range of different approaches to create artificial organelles: compartments with catalytic activity that add new function to living cells. In this review we will discuss three complementary lines of investigation. First, orthogonal chemistry approaches are discussed, which are based on the incorporation of catalytically active transition metal-containing nanoparticles in living cells. The second approach involves the use of premade hybrid nanoreactors, which show transient function when taken up by living cells. The third approach utilizes mostly genetic engineering methods to create bio-based structures that can be ultimately integrated with the cell's genome to make them constitutively active. The current state of the art and the scope and limitations of the field will be highlighted with selected examples from the three approaches.

Nanocage-Based Capture-Detection System for the Clinical Diagnosis of Autoimmune Disease

The detection of autoantibodies is critical for diagnosis of autoimmune diseases. However, the sensitivity is often limited by the properties of the antigens and the detection systems such as enzyme-linked immunosorbent assay (ELISA). Here, employing the multidisplay ability of ferritin, a highly sensitive nanocage-based capture-detection system is designed, of which the sensitivity is 100-1000-fold higher than that of conventional ELISA methods. The capture nanocages are constructed by displaying the primary Sjögren's syndrome (pSS)-related antigenic peptides on ferritin nanocage, which present epitopes effectively and high affinity, leading to tenfold higher capture capability for autoantibodies. Human IgG Fc-binding peptides are also engineered on ferritin nanocage, which enable high binding affinity and efficient horseradish peroxidase (HRP)-labeling. Compared with commercial HRP-conjugated anti-human IgG antibody, the nanocage-based detecting probe exhibited more than tenfold increased sensitivity. Autoantibodies are then examined in 91 sera from patients with pSS, 51 from rheumatoid arthritis, 54 from systemic lupus erythematosus, and 55 from healthy individuals by using the nanocage-based ELISA. The results indicate that the nanocage-based capture-detection system is an effective detection platform and provide a novel and more sensitive method for the diagnosis of autoimmune diseases.

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.

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

Protein nanocages represent a class of nanovehicles for a variety of applications. However, precise manipulation of self-assembly behavior of these protein nanocages in response to multiple external stimuli for custom-tailored applications remains challenging. Herein, we established a simple but effective strategy for controlling protein nanocage self-assembly that combines a dual property of His motifs (their significantly pH-dependent protonation state and their capacity to coordinate with transition metals) with its high symmetry. With this strategy, we enabled two different ferritin nanocages to disassemble into protein tetramers under neutral solution by introducing His₆ motifs at the 4-fold channel interfaces. Notably, these tetramers are able to self-assemble into ferritin-like protein nanocages in response to multiple external stimuli such as transition metal ions and pH, and vice versa, indicative of a reversible self-assembly process. Furthermore, such His-mediated reversible protein self-assembly has been explored for encapsulation of bioactive cargo molecules within these reconstituted protein nanocages with higher loading efficiency under milder conditions as compared to the reported acid denaturation encapsulation method for ferritin.

Ferritin Nanocage: A Versatile Nanocarrier Utilized in the Field of Food, Nutrition, and Medicine

Compared with other nanocarriers such as liposomes, mesoporous silica, and cyclodextrin, ferritin as a typical protein nanocage has received considerable attention in the field of food, nutrition, and medicine owing to its inherent cavity size, excellent water solubility, and biocompatibility. Additionally, ferritin nanocage also serves as a versatile bio-template for the synthesis of a variety of nanoparticles. Recently, scientists have explored the ferritin nanocage structure for encapsulation and delivery of guest molecules such as nutrients, bioactive molecules, anticancer drugs, and mineral metal ions by taking advantage of its unique reversible disassembly and reassembly property and biomineralization. In this review, we mainly focus on the preparation and structure of ferritin-based nanocarriers, and regulation of their self-assembly. Moreover, the recent advances of their applications in food nutrient delivery and medical diagnostics are highlighted. Finally, the main challenges and future development in ferritin-directed nanoparticles’ synthesis and multifunctional applications are discussed.

Connectability of protein cages

Regular, hollow proteinaceous nanoparticles are widespread in nature. The well-defined structures as well as diverse functions of naturally existing protein cages have inspired the development of new nanoarchitectures with desired capabilities. In such approaches, a key functionality is "connectability". Engineering of interfaces between cage building blocks to modulate intra-cage connectability leads to protein cages with new morphologies and assembly-disassembly properties. Modification of protein cage surfaces to control inter-cage connectability enables their arrangement into lattice-like nanomaterials. Here, we review the current progress in control of intra- and inter-cage connectability for protein cage-based nanotechnology development.

AB loop engineered ferritin nanocages for drug loading under benign experimental conditions

Human ferritin has been explored as a potential drug nanocarrier, but extreme conditions (pH ≤ 2.0) are required for the encapsulation of drugs. Here, by engineering the AB loop of ferritin, we obtained a new ferritin variant with no new pores, which can disassemble at pH 3.0 or 4.0 and reassemble at pH 7.0. Consequently, under mild conditions, drugs can be encapsulated within this new ferritin nanocage.

Ferritin variants: inspirations for rationally designing protein nanocarriers

Ferritin, a natural iron storage protein, is endowed with a unique structure, the ability to self-assemble and excellent physicochemical properties. Beyond these, genetic manipulation can easily tune the structure and functions of ferritin nanocages, which further expands the biomedical applications of ferritin. Here, we focus on human H-ferritin, a recently discovered ligand of transferrin receptor 1, to review its derived variants and related structures and properties. We hope this review will provide new insights into how to rationally design versatile protein cage nanocarriers for effective disease treatment.

Design and site-directed compartmentalization of gold nanoclusters within the intrasubunit interfaces of ferritin nanocage

BACKGROUND

Protein nanocages have emerged as popular nanocarriers for either drug delivery or biotemplates for the preparation of nanomaterials. However, only three interfaces, namely exterior surface, intersubunit and inner cavity, have been used as reaction sites for the above purposes with all known protein nanocages. On the other hand, how to control the site of Au NCs formed within a targeted protein template while maintaining the functionality of protein itself remains challenging.

RESULTS

In this work, inspired by compartmentalization in living systems, we firstly come up with the conception of "intrasubunit interfaces", located within subunit of protein nanocage. We built a new, specific compartment for fabrication of gold nanoclusters by genetic modification of the inherent ferroxidase center located within four-α-helix bundle of each ferritin subunit. This newly built compartment not only realizes the site-directed synthesis of gold nanoclusters but also has no effect on the functionality of ferritin itself such as encapsulation by its inner cavity. These redesigned composites can be further applied as fluorescent imaging agent and carriers for preparation of hybrid nanomaterials.

CONCLUSIONS

The designing strategy of intrasubunit interfaces opens a new way for future applications of cage-like proteins.

Designed Two- and Three-Dimensional Protein Nanocage Networks Driven by Hydrophobic Interactions Contributed by Amyloidogenic Motifs

Precise manipulation of protein self-assembly by noncovalent interactions into programmed networks to mimic naturally occurring nanoarchitectures in living organisms is a challenge due to its structural heterogeneity, flexibility, and complexity. Herein, by taking advantage of both the hydrophobic forces contributed by the "GLMVG" motif, a kind of amyloidogenic motif (AM), and the high symmetry of protein nanocages, we have built an effective protein self-assembly strategy for the construction of two-dimensional (2D) or three-dimensional (3D) protein nanocage arrays. According to this strategy, "GLMVG" AMs from β-amyloid 42 were grafted onto the outer surface of a 24-mer ferritin nanocage close to its C₄ symmetry channels, initially resulting in the production of subgrade 2D nanocage arrays and ultimately generating 3D highly ordered arrays with a simple cubic packing pattern as the reaction time increases. More importantly, the reversibility and the formation rate of these protein arrays can be modulated by pH. This work provides a de novo design strategy for accurate control over 2D or 3D protein self-assemblies.

Disulfide-mediated conversion of 8-mer bowl-like protein architecture into three different nanocages

Constructing different protein nanostructures with high-order discrete architectures by using one single building block remains a challenge. Here, we present a simple, effective disulfide-mediated approach to prepare a set of protein nanocages with different geometries from single building block. By genetically deleting an inherent intra-subunit disulfide bond, we can render the conversion of an 8-mer bowl-like protein architecture (NF-8) into a 24-mer ferritin-like nanocage in solution, while selective insertion of an inter-subunit disulfide bond into NF-8 triggers its conversion into a 16-mer lenticular nanocage. Deletion of the same intra-subunit disulfide bond and insertion of the inter-subunit disulfide bond results in the conversion of NF-8 into a 48-mer protein nanocage in solution. Thus, in the laboratory, simple mutation of one protein building block can generate three different protein nanocages in a manner that is highly reminiscent of natural pentamer building block originating from viral capsids that self-assemble into protein assemblies with different symmetries.

Disulfide-mediated reversible two-dimensional self-assembly of protein nanocages

Disulfide-mediated 2D protein self-assembly was achieved by single point mutation of hot spots at the C₄ interface of ferritin.

On-Axis Alignment of Protein Nanocage Assemblies from 2D to 3D through the Aromatic Stacking Interactions of Amino Acid Residues

Aromatic-aromatic interactions between natural aromatic amino acids Phe, Tyr, and Trp play crucial roles in protein-protein recognition and protein folding. However, the function of such interactions in the preparation of different dimensional, ordered protein superstructures has not been recognized. Herein, by a combination of the directionality of the symmetry axes of protein building blocks and the strength of the aromatic-aromatic interactions coming from a group of aromatic amino acid residues, we built an engineering strategy to construct protein superlattices. Based on this strategy, substitution of single amino acid residue Glu162 around the C₄ rotation axes near the outer surface of 24-mer ferritin nanocage with Phe, Tyr, and Trp, respectively, resulted in 2D and 3D protein superlattices where protein cages are aligned along the C₄ axes, imposing a fixed disposition of neighboring ferritins. The self-assembly of these superlattices is reversible, which can be tuned by external stimuli (salt concentration or pH). Moreover, these superlattices can serve as biotemplates for the fabrication of 2D and 3D inorganic nanoparticle arrays.

Precision engineering of targeted nanocarriers

Since their introduction in 1980, the number of advanced targeted nanocarrier systems has grown considerably. Nanocarriers capable of targeting single receptors, multiple receptors, or multiple epitopes have all been used to enhance delivery efficiency and selectivity. Despite tremendous progress, preclinical studies and clinically translatable nanotechnology remain disconnected. The disconnect in targeting efficacy may stem from poorly-understood factors such as receptor clustering, spatial control of targeting ligands, ligand mobility, and ligand architecture. Further, the relationship between receptor distribution and ligand architecture remains elusive. Traditionally, targeted nanocarriers were engineered assuming a "static" target. However, it is becoming increasingly clear that receptor expression patterns change in response to external stimuli and disease progression. Here, we discuss how cutting-edge technologies will enable a better characterization of the spatiotemporal distribution of membrane receptors and their clustering. We further describe how this will enable the design of new nanocarriers that selectively target the site of disease. Ultimately, we explore how the precision engineering of targeted nanocarriers that adapt to receptor dynamics will have the potential to drive nanotechnology to the forefront of therapy and make targeted nanomedicine a clinical reality. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Lipid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.