Self-Assembled Materials Made from Functional Recombinant Proteins

Rational design and engineering of polypeptide/protein vesicles for advanced biological applications

Synthetic vesicles have gained considerable popularity in recent years for numerous biological and medical applications. Among the various types of synthetic vesicles, the utilization of polypeptides and/or proteins as fundamental constituents has garnered significant interest for vesicle construction owing to the unique bio-functionalities inherent in rationally designed amino acid sequences. Especially the incorporation of functional proteins onto the vesicle surface facilitates a wide range of advanced biological applications that are not easily attainable with traditional building blocks, such as lipids and polymers. The main goal of this review is to provide a comprehensive overview of the latest advancements in polypeptide/protein vesicles. Moreover, this review encompasses the rational design and engineering strategies employed in the creation of polypeptide/protein vesicles, including the synthesis of building blocks, the modulation of their self-assembly, as well as their diverse applications. Furthermore, this work includes an in-depth discussion of the key challenges and opportunities associated with polypeptide/protein vesicles, providing valuable insights for future research. By offering an up-to-date review of this burgeoning field of polypeptide/protein vesicle research, this review will shed light on the potential applications of these biomaterials.

Probing the Biosafety of Implantable Artificial Secretory Granules for the Sustained Release of Bioactive Proteins

Among bio-inspired protein materials, secretory protein microparticles are of clinical interest as self-contained, slow protein delivery platforms that mimic secretory granules of the human endocrine system, in which the protein is both the drug and the scaffold. Upon subcutaneous injection, their progressive disintegration results in the sustained release of the building block polypeptides, which reach the bloodstream for systemic distribution and subsequent biological effects. Such entities are easily fabricated in vitro by Zn-assisted cross-molecular coordination of histidine residues. Using cationic Zn for the assembly of selected pure protein species and in the absence of any heterologous holding material, these granules are expected to be nontoxic and therefore adequate for different clinical uses. However, such presumed biosafety has not been so far confirmed and the potential protein dosage threshold not probed yet. By selecting the receptor binding domain (RBD) from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein as a model protein and using a mouse lab model, we have explored the toxicity of RBD-made secretory granules at increasing doses up to ∼100 mg/kg of animal weight. By monitoring body weight and biochemical blood markers and through the histological scrutiny of main tissues and organs, we have not observed systemic toxicity. Otherwise, the bioavailability of the material was demonstrated by the induction of specific antibody responses. The presented data confirm the intrinsic biosafety of artificial secretory granules made by recombinant proteins and prompt their further clinical development as self-contained and dynamic protein reservoirs.

Temperature-responsive membrane permeability of recombinant fusion protein vesicles

In this study, we investigate the changes in the permeability of the recombinant fusion protein vesicles with different membrane structures as a function of solution temperature. The protein vesicles are self-assembled from recombinant fusion protein complexes composed of an mCherry fused with a glutamic acid-rich leucine zipper and a counter arginine-rich leucine zipper fused with an elastin-like polypeptide (ELP). We have found that the molecular weight cut-off (MWCO) of the protein vesicle membranes varies inversely with solution temperature by monitoring the transport of fluorescent-tagged dextran dyes with different molecular weights. The temperature-responsiveness of the protein vesicle membranes is obtained from the lower critical solution temperature behavior of ELP in the protein building blocks. Consequently, the unique vesicle membrane structures with different single-layered and double-layered ELP organizations impact the sensitivity of the permeability responses of the protein vesicles. Single-layered protein vesicles with the ELP domains facing the interior show more drastic permeability changes as a function of temperature than double-layered protein vesicles in which ELP blocks are buried inside the membranes. This work about the temperature-responsive membrane permeability of unique protein vesicles will provide design guidelines for new biomaterials and their applications, such as drug delivery and synthetic protocell development.

Highly Hydrophobic Films of Engineered Silk Proteins by a Simple Deposition Method

Molecular engineering of protein structures offers a uniquely versatile route for novel functionalities in materials. Here, we describe a method to form highly hydrophobic thin films using genetically engineered spider silk proteins. We used structurally engineered protein variants containing ADF3 and AQ12 spider silk sequences. Wetting properties were studied using static and dynamic contact angle measurements. Solution conditions and the surrounding humidity during film preparation were key parameters to obtain high hydrophobicity, as shown by contact angles in excess of 120°. Although the surface layer was highly hydrophobic, its structure was disrupted by the added water droplets. Crystal-like structures were found at the spots where water droplets had been placed. To understand the mechanism of film formation, different variants of the proteins, the topography of the films, and secondary structures of the protein components were studied. The high contact angle in the films demonstrates that the conformations that silk proteins take in the protein layer very efficiently expose their hydrophobic segments. This work reveals a highly amphiphilic nature of silk proteins and contributes to an understanding of their assembly mechanisms. It will also help in designing diverse technical uses for recombinant silk.

Cell-sized asymmetric phospholipid-amphiphilic protein vesicles with growth, fission, and molecule transportation

Lipid vesicles, which mimic cell membranes in structure and components, have been used to study the origin of life and artificial cell construction. A different approach to developing cell-mimicking systems focuses on the formation of protein- or polypeptide-based vesicles. However, micro-sized protein vesicles that are similar in membrane dynamics to the cell and that reconstitute membrane proteins are difficult to form. In this study, we generated cell-sized asymmetric phospholipid-amphiphilic protein (oleosin) vesicles that allow the reconstitution of membrane proteins and the growth and fission of vesicles. These vesicles are composed of a lipid membrane on the outer leaflet and an oleosin membrane on the inner leaflet. Further, we elucidated a mechanism for the growth and fission of cell-sized asymmetric phospholipid-oleosin vesicles by feeding phospholipid micelles. Our asymmetric phospholipid-oleosin vesicles with the advantages of the lipid leaflet and the protein leaflet will potentially promote understanding of biochemistry and synthetic biology.

Heterogeneous Synthetic Vesicles toward Artificial Cells: Engineering Structure and Composition of Membranes for Multimodal Functionalities

The desire to develop artificial cells to imitate living cells in synthetic vesicle platforms has continuously increased over the past few decades. In particular, heterogeneous synthetic vesicles made from two or more building blocks have attracted attention for artificial cell applications based on their multifunctional modules with asymmetric structures. In addition to the traditional liposomes or polymersomes, polypeptides and proteins have recently been highlighted as potential building blocks to construct artificial cells owing to their specific biological functionalities. Incorporating one or more functionally folded, globular protein into synthetic vesicles enables more cell-like functions mediated by proteins. This Review highlights the recent research about synthetic vesicles toward artificial cell models, from traditional synthetic vesicles to protein-assembled vesicles with asymmetric structures. We aim to provide fundamental and practical insights into applying knowledge on molecular self-assembly to the bottom-up construction of artificial cell platforms with heterogeneous building blocks.

Genetically encoded elastin-like polypeptide nanoparticles for drug delivery

Small molecule drugs suffer from poor in vivo half-life, rapid degradation, and systemic off-target toxicity. To address these issues, researchers have developed nanoparticles that significantly enhance the delivery of many drugs while reducing their toxicity and improving targeting to specific organs. Recombinantly synthesized biomaterials such as elastin-like polypeptides (ELPs) have unique attributes that greatly facilitate the rational design of nanoparticles for drug delivery. These attributes include biocompatibility, precise control over amino acid sequence design, and stimuli-responsive self-assembly into nanostructures that can be loaded with a range of drugs to enhance their pharmacokinetics and pharmacodynamics, significantly improving their therapeutic efficacy over the free drugs. This review summarizes recent developments in genetically encoded, self-assembling ELP nanoparticles and their applications for drug delivery.

Polymer-Surfactant Driven Interactions and the Resultant Microstructure in Protein-Containing Liquid Crystal Droplets

Integration of molecular liquid crystals (LCs) with functional proteins can provide new class of materials for potential applications in optical biosensing. However, hydrophobic nematic LCs (length ∼ 1-2 nm) and hydrophilic proteins, size ∼ O (nm), do not intermix without chemical modification of at least one of them. Bioconjugation of proteins with a polyethylene glycol-based polymeric surfactant (PS) can provide a core-shell system that is sequestered within nonaqueous LC (4-cyano-4'-pentylbiphenyl) microdroplets. However, the nature of interactions between the components and detailed understanding of the resultant hybrid microstructure remains unclear. Here, using a combination of isothermal titration calorimetry (ITC), fluorescence microscopy, and infrared-imaging spectroscopy, we show that strong hydrophobic interactions between the LC and PS drives the sequestration of a myoglobin-PS (Mb-PS; dispersed in the aqueous phase) into the LC spherical microdroplets or even into a bulk LC phase. The average values of both, the binding constant and the standard molar enthalpy change, are increased by approximately a factor of 2.5 times when the unmodified Mb is conjugated to the PS. Small-angle X-ray scattering studies reveal that LC molecules act as a solvent for the Mb-PS conjugate; furthermore, the LC long-range order is disturbed due to mixing, as exemplified by the change in its coherence length from 8.9 to 5.7 nm. Detailed all-atomistic molecular dynamic simulations for a three-component PS-water-LC system show a change in interaction energy of -144 kJ mol^-1 PS^-1 upon the contact of PS chains (initially dispersed in water) with LC and agree with the ITC experiments.

Self-assembly of the monohydroxy triterpenoid lupeol yielding nano-fibers, sheets and gel: environmental and drug delivery applications

Lupeol is a medicinally important naturally abundant triterpenoid having a 6-6-6-6-5 fused pentacyclic backbone and one polar secondary "-OH" group at the C3 position of the "A" ring. It was extracted from the dried outer bark of Bombax ceiba and its self-assembly properties were investigated in different neat organic as well as aquous-organic binary liquid mixtures. The triterpenoid having only one polar "-OH" group and a rigid lipophilic backbone self-assembled in neat organic non-polar liquids like n-hexane, n-heptane, n-octane and polar liquids like DMSO, DMF, DMSO-H₂O, DMF-H₂O, and EtOH-H₂O yielding supramolecular gels via formation of nano to micrometre long self-assembled fibrillar networks (SAFINs). Morphological investigation of the self-assemblies was carried out by field emission scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, optical microscopy, concentration dependent FTIR and wide angle X-ray diffraction studies. The mechanical properties of the gels were studied by concentration dependent rheological studies in different solvents. The gels were capable of removing toxic micro-pollutants like rhodamine-B and 5,6-carboxyfluorescein as well as the toxic heavy metal Cr(vi) from contaminated water. Moreover release of the chemotherapeutic drug doxorubicin from a drug loaded gel in PBS buffer at pH 7.2 has also been demonstrated by spectrophotometry.

Garland, Flower, and Petals via a Hierarchical Self-Assembly of Ursane-Type Triterpenoid Uvaol

Uvaol, a 6-6-6-6-6 pentacyclic dihydroxy ursane-type triterpenoid, is isolable from different parts of plants Plumeria rubra, Olea europaea, Nerium oleander, Lavandula pedunculta, and Malus domestica. It is also obtained by a one-step reduction of naturally occurring triterpenoid ursolic acid. Herein, we report the first self-assembly properties of uvaol in different neat organic liquids and aqueous organic binary liquid mixtures. Spontaneous self-assembly of uvaol in different neat liquids and binary liquid mixtures yielded garland, flower, and petal-like porous superstructures of nano- to micrometer dimensions. Utilization of self-assemblies has been demonstrated in generation of anticancer drug conjugates and the removal of carcinogenic and toxic chemicals.

Thermo-Viscoelastic Response of Protein-Based Hydrogels

Because of the bioactivity and biocompatibility of protein-based gels and the reversible nature of bonds between associating coiled coils, these materials demonstrate a wide spectrum of potential applications in targeted drug delivery, tissue engineering, and regenerative medicine. The kinetics of rearrangement (association and dissociation) of the physical bonds between chains has been traditionally studied in shear relaxation tests and small-amplitude oscillatory tests. A characteristic feature of recombinant protein gels is that chains in the polymer network are connected by temporary bonds between the coiled coil complexes and permanent cross-links between functional groups of amino acids. A simple model is developed for the linear viscoelastic behavior of protein-based gels. Its advantage is that, on the one hand, the model only involves five material parameters with transparent physical meaning and, on the other, it correctly reproduces experimental data in shear relaxation and oscillatory tests. The model is applied to study the effects of temperature, the concentration of proteins, and their structure on the viscoelastic response of hydrogels.

On the Search of a Silver Bullet for the Preparation of Bioinspired Molecular Electrets with Propensity to Transfer Holes at High Potentials

Biological structure-function relationships offer incomparable paradigms for charge-transfer (CT) science and its implementation in solar-energy engineering, organic electronics, and photonics. Electrets are systems with co-directionally oriented electric dopes with immense importance for CT science, and bioinspired molecular electrets are polyamides of anthranilic-acid derivatives with designs originating from natural biomolecular motifs. This publication focuses on the synthesis of molecular electrets with ether substituents. As important as ether electret residues are for transferring holes under relatively high potentials, the synthesis of their precursors presents formidable challenges. Each residue in the molecular electrets is introduced as its 2-nitrobenzoic acid (NBA) derivative. Hence, robust and scalable synthesis of ether derivatives of NBA is essential for making such hole-transfer molecular electrets. Purdie-Irvine alkylation, using silver oxide, produces with 90% yield the esters of the NBA building block for iso-butyl ether electrets. It warrants additional ester hydrolysis for obtaining the desired NBA precursor. Conversely, Williamson etherification selectively produces the same free-acid ether derivative in one-pot reaction, but a 40% yield. The high yields of Purdie-Irvine alkylation and the selectivity of the Williamson etherification provide important guidelines for synthesizing building blocks for bioinspired molecular electrets and a wide range of other complex ether conjugates.

Recent developments in microfluidic synthesis of artificial cell-like polymersomes and liposomes for functional bioreactors

Recent advances in droplet microfluidics have led to the fabrication of versatile vesicles with a structure that mimics the cellular membrane. These artificial cell-like vesicles including polymersomes and liposomes effectively enclose an aqueous core with well-defined size and composition from the surrounding environment to implement various biological reactions, serving as a diverse functional reactor. The advantage of realizing various biological phenomena within a compartment separated by a membrane that resembles a natural cell membrane is actively explored in the fields of synthetic biology as well as biomedical applications including drug delivery, biosensors, and bioreactors, to name a few. In this Perspective, we first summarize various methods utilized in producing these polymersomes and liposomes. Moreover, we will highlight some of the recent advances in the design of these artificial cell-like vesicles for functional bioreactors and discuss the current issues and future perspectives.

Dual Self-Assembled Nanostructures from Intrinsically Disordered Protein Polymers with LCST Behavior and Antimicrobial Peptides

Antimicrobial peptides (AMPs) have attracted great interest as they constitute one of the most promising alternatives against drug-resistant infections. Their amphipathic nature not only provides them antimicrobial and immunomodulatory properties but also the ability to self-assemble into supramolecular nanostructures. Here, we propose their use as self-assembling domains to drive hierarchical organization of intrinsically disordered protein polymers (IDPPs). Using a modular approach, hybrid protein-engineered polymers were recombinantly produced, thus combining designer AMPs and a thermoresponsive IDPP, an elastin-like recombinamer (ELR). We exploited the ability of these AMPs and ELRs to self-assemble to develop supramolecular nanomaterials by way of a dual-assembly process. First, the AMPs trigger the formation of nanofibers; then, the thermoresponsiveness of the ELRs enables assembly into fibrillar aggregates. The interplay between the assembly of AMPs and ELRs provides an innovative molecular tool in the development of self-assembling nanosystems with potential use for biotechnological and biomedical applications.

Tuning the Structural Integrity and Mechanical Properties of Globular Protein Vesicles by Blending Crosslinkable and NonCrosslinkable Building Blocks

Vesicles made from functionally folded, globular proteins that perform specific biological activities, such as catalysis, sensing, or therapeutics, show potential applications as artificial cells, microbioreactors, or protein drug delivery vehicles. The mechanical properties of vesicle membranes, including the elastic modulus and hardness, play a critical role in dictating the stability and shape transformation of the vesicles under external stimuli triggers. Herein, we have developed a strategy to tune the mechanical properties and integrity of globular protein vesicle (GPV) membranes of which building molecules are recombinant fusion protein complexes: a mCherry fused with an acidic leucine zipper (mCherry-Z_E) and a basic leucine zipper fused with an elastin-like polypeptide (Z_R-ELP). To control the mechanical properties of GPVs, we introduced a nonstandard amino acid (para-azidophenylalanine (pAzF)) into the ELP domains (ELP-X), which enabled the creation of crosslinked vesicles under ultraviolet (UV) irradiation. Crosslinked GPVs made from mCherry-Z_E/Z_R-ELP-X complexes presented higher stability than noncrosslinked GPVs under hypotonic osmotic stress. The degree of swelling of GPVs increased as less crosslinking was achieved in the vesicle membranes, which resulted in the disassembly of GPVs into membraneless coacervates. Nanoindentation by atomic force microscopy (AFM) confirmed that the stiffness and Young's elastic modulus of GPVs increase as the blending molar ratio of Z_R-ELP-X to Z_R-ELP increases to make vesicles. The results obtained in this study suggest a rational design to make GPVs with tunable mechanical properties for target applications by simply varying the blending ratio of Z_R-ELP and Z_R-ELP-X in the vesicle self-assembly.

A comparative study of materials assembled from recombinant K31 and K81 and extracted human hair keratins

Natural biopolymers have found success in tissue engineering and regenerative medicine applications. Their intrinsic biocompatibility and biological activity make them well suited for biomaterials development. Specifically, keratin-based biomaterials have demonstrated utility in regenerative medicine applications including bone regeneration, wound healing, and nerve regeneration. However, studies of structure-function relationships in keratin biomaterials have been hindered by the lack of homogeneous preparations of materials extracted and isolated from natural sources such as wool and hair fibers. Here we present a side-by-side comparison of natural and recombinant human hair keratin proteins K31 and K81. When combined, the recombinant proteins (i.e. rhK31 and rhK81) assemble into characteristic intermediate filament-like fibers. Coatings made from natural and recombinant dimers were compared side-by-side and investigated for coating characteristics and cell adhesion. In comparison to control substrates, the recombinant keratin materials show a higher propensity for inducing involucrin and hence, maturation in terms of potential skin cell differentiation.

Charge Density as a Molecular Modulator of Nanostructuration in Intrinsically Disordered Protein Polymers

Intrinsically disordered protein polymers (IDPPs) have attracted a lot of attention in the development of bioengineered devices and for use as study models in molecular biology because of their biomechanical properties and stimuli-responsiveness. The present study aims to understand the effect of charge density on the self-assembly of IDPPs. To that end, a library of recombinant IDPPs based on an amphiphilic diblock design with different charge densities was bioproduced, and their supramolecular assembly was characterized on the nano-, meso-, and microscale. Although the phase transition was driven by the collapse of hydrophobic moieties, the hydrophilic block composition strongly affected hierarchical assembly and, therefore, enabled the production of new molecular architectures, thus leading to new dynamics that govern the liquid-gel transition. These results highlight the importance of electrostatic repulsion for the hierarchical assembly of IDPPs and provide insights into the manufacture of supramolecular protein-based materials.

Bioinspired Protein-Based Assembling: Toward Advanced Life-Like Behaviors

The ability of living organisms to perform structure, energy, and information-related processes for molecular self-assembly through compartmentalization and chemical transformation can possibly be mimicked via artificial cell models. Recent progress in the development of various types of functional microcompartmentalized ensembles that can imitate rudimentary aspects of living cells has refocused attention on the important question of how inanimate systems can transition into living matter. Hence, herein, the most recent advances in the construction of protein-bounded microcompartments (proteinosomes), which have been exploited as a versatile synthetic chassis for integrating a wide range of functional components and biochemical machineries, are critically summarized. The techniques developed for fabricating various types of proteinosomes are discussed, focusing on the significance of how chemical information, substance transportation, enzymatic-reaction-based metabolism, and self-organization can be integrated and recursively exploited in constructed ensembles. Therefore, proteinosomes capable of exhibiting gene-directed protein synthesis, modulated membrane permeability, spatially confined membrane-gated catalytic reaction, internalized cytoskeletal-like matrix assembly, on-demand compartmentalization, and predatory-like chemical communication in artificial cell communities are specially highlighted. These developments are expected to bridge the gap between materials science and life science, and offer a theoretical foundation for developing life-inspired assembled materials toward various applications.

Recent Advances in Allogeneic CAR-T Cells

In recent decades, great advances have been made in the field of tumor treatment. Especially, cell-based therapy targeting tumor associated antigen (TAA) has developed tremendously. T cells were engineered to have the ability to attack tumor cells by generating CAR constructs consisting of genes encoding scFv, a co-stimulatory domain (CD28 or TNFRSF9), and CD247 signaling domains for T cell proliferation and activation. Principally, CAR-T cells are activated by recognizing TAA by scFv on the T cell surface, and then signaling domains inside cells connected by scFv are subsequently activated to induce downstream signaling pathways involving T cell proliferation, activation, and production of cytokines. Many efforts have been made to increase the efficacy and persistence and also to decrease T cell exhaustion. Overall, allogeneic and universal CAR-T generation has attracted much attention because of their wide and prompt usage for patients. In this review, we summarized the current techniques for generation of allogeneic and universal CAR-T cells along with their disadvantages and limitations that still need to be overcome.

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-f]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.

PEP-FOLD design, synthesis, and characteristics of finger-like polypeptides

Polypeptides with finger-like structures can often intercalate into the grooves of DNA, thereby affecting DNA repair or activating gene transcription, both of which are crucial for the regulation of physiological processes. Their conserved amino acid sequence and simple structure have provided useful elements for the design and assembly of functional molecules. In this paper, using the C₂H₂ zinc finger domain and the PEP-FOLD3 online simulation platform 11 polypeptides containing 22 amino acid residues were designed. In addition, the CD spectroscopy was combined with the fluorescence spectroscopy to study the polypeptide structures and their interaction with DNA. Results showed that although addition of zinc ions affected the polypeptide structure, particularly of the polypeptides A4, B1, and B3, zinc ion was not an essential factor for increasing polypeptide-DNA interactions. Our study revealed an increase in the interaction strength between mutated polypeptides and DNA, suggesting that mutations disrupt polypeptide structure, and polypeptides interact with DNA by groove and electrostatic binding. Mutations at the 12th and 15th amino acid residues had the greatest effect. The stronger binding between A2 or B2 and DNA indicates that the polypeptide has a spatial structure that can stably interact with DNA. The structure and characteristics of these polypeptide domains can provide information for the design and development of new polypeptide functional molecules, which could have potential significance and applications. However, this information also suggests that there are many challenges facing polypeptide design due to the synergistic effects between the side chains of amino acid residues.

Self-assembly of naturally occurring stigmasterol in liquids yielding a fibrillar network and gel

Stigmasterol extracted from the leaves of Roscoea purpurea spontaneously self-assembled in liquids yielding a fibrillar network and gel.

Self-Assembly Toolbox of Tailored Supramolecular Architectures Based on an Amphiphilic Protein Library

The molecular structuring of complex architectures and the enclosure of space are essential requirements for technical and living systems. Self-assembly of supramolecular structures with desired shape, size, and stability remains challenging since it requires precise regulation of physicochemical and conformational properties of the components. Here a general platform for controlled self-assembly of tailored amphiphilic elastin-like proteins into desired supramolecular protein assemblies ranging from spherical coacervates over molecularly defined twisted fibers to stable unilamellar vesicles is introduced. The described assembly protocols efficiently yield protein membrane-based compartments (PMBC) with adjustable size, stability, and net surface charge. PMBCs demonstrate membrane fusion and phase separation behavior and are able to encapsulate structurally and chemically diverse cargo molecules ranging from small molecules to naturally folded proteins. The ability to engineer tailored supramolecular architectures with defined fusion behavior, tunable properties, and encapsulated cargo paves the road for novel drug delivery systems, the design of artificial cells, and confined catalytic nanofactories.

Biologically Inspired and Chemically Derived Methods for Glucose-Responsive Insulin Therapy

The controlled delivery of therapeutics in a manner responsive to physiological indicators has promise in realizing new therapeutic approaches to combat disease. This approach is especially relevant in the context of diabetes. Natural fluctuations in blood glucose seen in the healthy state, complete with peaks and troughs, are poorly regulated as a result of detrimental production or ineffective signaling of the insulin hormone. While several manifestations of diabetes are treated with regularly administered exogenous insulin, the present standard of care results in suboptimal glycemic management that poorly recreates natural hormone control, leading to long-term instability and a significantly increased risk for secondary health complications. New synthetic technologies that make insulin available only when needed, and at the exact dose required, have been explored under the broad vision of realizing a "fully synthetic pancreas." Yet, many challenges remain to realizing a technology that is appropriately responsive, safe, and well integrated into a manageable routine. Herein, many of the approaches explored thus far to sense physiological blood glucose and elicit response through the release of therapeutic insulin are summarized. The approaches point to a new, autonomous approach to managing diabetes with biomimetic therapy.

Protein-Engineered Functional Materials

Proteins are versatile macromolecules that can perform a variety of functions. In the past three decades, they have been commonly used as building blocks to generate a range of biomaterials. Owing to their flexibility, proteins can either be used alone or in combination with other functional molecules. Advances in synthetic and chemical biology have enabled new protein fusions as well as the integration of new functional groups leading to biomaterials with emergent properties. This review discusses protein-engineered materials from the perspectives of domain-based designs as well as physical and chemical approaches for crosslinked materials, with special emphasis on the creation of hydrogels. Engineered proteins that organize or template metal ions, bear noncanonical amino acids (NCAAs), and their potential applications, are also reviewed.

Self-assembly in elastin-like recombinamers: a mechanism to mimic natural complexity

The topic of self-assembled structures based on elastin-like recombinamers (ELRs, i.e., elastin-like polymers recombinantly bio-produced) has released a noticeable amount of references in the last few years. Most of them are intended for biomedical applications. In this review, a complete revision of the bibliography is carried out. Initially, the self-assembly (SA) concept is considered from a general point of view, and then ELRs are described and characterized based on their intrinsic disorder. A classification of the different self-assembled ELR-based structures is proposed based on their morphologies, paying special attention to their tentative modeling. The impact of the mechanism of SA on these biomaterials is analyzed. Finally, the implications of ELR SA in biological systems are considered.

The role of the side chain in the conformational and self-assembly patterns of C2-symmetric Val and Phe pseudopeptidic derivatives

Side chain as the main conformational and self-assembly structural factor for C₂-pseudopeptides.

Biomolecular Assemblies: Moving from Observation to Predictive Design

Biomolecular assembly is a key driving force in nearly all life processes, providing structure, information storage, and communication within cells and at the whole organism level. These assembly processes rely on precise interactions between functional groups on nucleic acids, proteins, carbohydrates, and small molecules, and can be fine-tuned to span a range of time, length, and complexity scales. Recognizing the power of these motifs, researchers have sought to emulate and engineer biomolecular assemblies in the laboratory, with goals ranging from modulating cellular function to the creation of new polymeric materials. In most cases, engineering efforts are inspired or informed by understanding the structure and properties of naturally occurring assemblies, which has in turn fueled the development of predictive models that enable computational design of novel assemblies. This Review will focus on selected examples of protein assemblies, highlighting the story arc from initial discovery of an assembly, through initial engineering attempts, toward the ultimate goal of predictive design. The aim of this Review is to highlight areas where significant progress has been made, as well as to outline remaining challenges, as solving these challenges will be the key that unlocks the full power of biomolecules for advances in technology and medicine.

Programed Assembly of Nucleoprotein Nanoparticles Using DNA and Zinc Fingers for Targeted Protein Delivery

With a growing number of intracellular drug targets and the high efficacy of protein therapeutics, the targeted delivery of active proteins with negligible toxicity is a challenging issue in the field of precision medicine. Herein, a programed assembly of nucleoprotein nanoparticles (NNPs) using DNA and zinc fingers (ZnFs) for targeted protein delivery is presented. Two types of ZnFs with different sequence specificities are genetically fused to a targeting moiety and a protein cargo, respectively. Double-stranded DNA with multiple ZnF-binding sequences is grafted onto inorganic nanoparticles, followed by conjugation with the ZnF-fused proteins, generating the assembly of NNPs with a uniform size distribution and high stability. The approach enables controlled loading of a protein cargo on the NNPs, offering a high cytosolic delivery efficiency and target specificity. The utility and potential of the assembly as a versatile protein delivery vehicle is demonstrated based on their remarkable antitumor activity and target specificity with negligible toxicity in a xenograft mice model.

How Do Amides Affect the Electronic Properties of Pyrene?

The electronic properties of amide linkers, which are intricate components of biomolecules, offer a wealth of unexplored possibilities. Herein, we demonstrate how the different modes of attaching an amide to a pyrene chromophore affect the electrochemical and optical properties of the chromophore. Thus, although they cause minimal spectral shifts, amide substituents can improve either the electron-accepting or electron-donating capabilities of pyrene. Specifically, inversion of the amide orientation shifts the reduction potentials by 200 mV. These trends indicate that, although amides affect to a similar extent the energies of the ground and singlet excited states of pyrene, the effects on the doublet states of its radical ions are distinctly different. This behavior reflects the unusually strong orientation dependence of the resonance effects of amide substituents, which should extend to amide substituents on other types of chromophores in general. These results represent an example where the Hammett sigma constants fail to predict substituent effects on electrochemical properties. On the other hand, Swain-Lupton parameters are found to be in good agreement with the observed trends. Examination of the frontier orbitals of the pyrene derivatives and their components reveals the underlying reason for the observed amide effects on the electronic properties of this polycyclic aromatic hydrocarbon and points to key molecular-design strategies for electronic and energy-conversion systems.

Supraparticles: Functionality from Uniform Structural Motifs

Under the right process conditions, nanoparticles can cluster together to form defined, dispersed structures, which can be termed supraparticles. Controlling the size, shape, and morphology of such entities is a central step in various fields of science and technology, ranging from colloid chemistry and soft matter physics to powder technology and pharmaceutical and food sciences. These diverse scientific communities have been investigating formation processes and structure/property relations of such supraparticles under completely different boundary conditions. On the fundamental side, the field is driven by the desire to gain maximum control of the assembly structures using very defined and tailored colloidal building blocks, whereas more applied disciplines focus on optimizing the functional properties from rather ill-defined starting materials. With this review article, we aim to provide a connecting perspective by outlining fundamental principles that govern the formation and functionality of supraparticles. We discuss the formation of supraparticles as a result of colloidal properties interplaying with external process parameters. We then outline how the structure of the supraparticles gives rise to diverse functional properties. They can be a result of the structure itself (emergent properties), of the colocalization of different, functional building blocks, or of coupling between individual particles in close proximity. Taken together, we aim to establish structure-property and process-structure relationships that provide unifying guidelines for the rational design of functional supraparticles with optimized properties. Finally, we aspire to connect the different disciplines by providing a categorized overview of the existing, diverging nomenclature of seemingly similar supraparticle structures.

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Multiple-Responsive Hierarchical Self-Assemblies of a Smart Supramolecular Complex: Regulation of Noncovalent Interactions

We herein report a smart amphiphilic supramolecular complex ([MimA-EDA-MimA]@[DBS]₂) with stimuli-responsive self-assembly, constructed by 3-(3-formyl-4-hydroxybenzyl)-1-methylimidazolium chloride (MimACl), sodium dodecyl benzene sulfonate (SDBS), and ethylenediamine (EDA). The self-assembly of [MimA-EDA-MimA]@[DBS]₂ shows triple-sensitivities in response to pH, concentration, and salt. At a low pH, only micelles are formed, which can transform into vesicles spontaneously when the pH increases to 11.8. Vesicles can gradually fuse into vesicle clusters and elongated assemblies with increasing concentration of [MimA-EDA-MimA]@[DBS]₂. Chainlike aggregates, ringlike aggregates, or giant vesicles can be formed by adding inorganic salts (i.e., NaCl and NaNO₃), which could be derived from the membrane fusion of vesicles. The noncovalent interactions, including π-π stacking, hydrogen bonding, and electrostatic interactions, were found to be responsible for the topology evolution of assemblies. Thus, it provides an opportunity to construct smart materials through the regulation of the role of noncovalent interactions in self-assembly.

Self-assembled nanomaterials for synergistic antitumour therapy

Recent progress on self-assembled nanodrugs for anticancer treatment was discussed.

Supramolecular gelatons: towards the design of molecular gels

The concept of supramolecular gelatons for the design of gels was proposed and described.

First in situ vesicular self-assembly of ‘binols’ generated by a two-component aerobic oxidation reaction

Generation of vesicular self-assemblies from natural and synthetic components has been in the frontiers of research in recent years for an improved understanding of the self-assembly process and also because of its prospective and realized applications in the areas of advanced materials, biotechnology and medicine. In the present work, we report the first example of the in situ generation of vesicular self-assemblies during an aerobic coupling reaction. The two precursor 2-naphthol units, having hydrogen bond donor–acceptor groups with appended alkyl chains, yielded binol (2,2′-dihydroxy-1,1′-binaphthyl) derivatives by aerobic coupling that spontaneously self-assembled in situ, yielding vesicular self-assemblies and gels. The morphology of the self-assemblies has been characterized by various optical, electron and atomic force microscopic techniques. The vesicular self-assemblies obtained in the liquids were capable of entrapping fluorophores such as rhodamine-B and carboxy fluorescein including the anticancer drug doxorubicin. The entrapped fluorophores could also be released by sonication or by rupture of vesicles. The supramolecular gels obtained in binary solvent mixtures showed improved gelation abilities with increase in the alkyl chain lengths as reflected by their minimum gelator concentration (mgcs) values, gel to sol transition temperatures (T_gel) and rheology properties. The results described here are also the first demonstration of gelation during an aerobic coupling reaction.

Binol derivatives, obtained by aerobic coupling of two 2-naphthol derivatives having H-bond donor–acceptor groups and appended alkyl chains, spontaneously self-assembled in situ yielding vesicular self-assemblies and gels.

Self-assembly of amphiphilic truncated cones to form hollow nanovesicles

To mimic the unique properties of capsid (protein shell of a virus), we performed Brownian dynamics simulations of the self-assembly of amphiphilic truncated cone particles with anisotropic interactions. The particle shape of a truncated cone in our simulations depended on the cone angle θ, truncated height h_c and particle type (A_xB_y and B_xA_yB_z). The hydrophobic A moieties and hydrophilic B moieties are responsible for attractive and repulsive interactions, respectively. By varying the particle shape, truncated cones can assemble into hollow and vesicle-like clusters with a specific cluster size N. To assemble into hollow vesicles, the truncated height h_c must be below a critical value. When h_c exceeds this critical value, malformation will occur. The dynamics shows that the vesicle formation occurs in three stages: initially the growth is slow, then rapid, and finally it slows down. The truncated height h_c has a stronger impact on the growth kinetics than the cone angle θ or the particle type. We explored how the cluster packing depended on the cooling rate and particle number as well as discussing the relationship between the cluster geometry and the interparticle interactions. Further, we also discuss possible methods to experimentally prepare the truncated cones. The results of our work deepen our understanding of the self-assembly behavior of truncated cones and our results will aid the effective design of particle building blocks for novel nanostructures.

To mimic the unique properties of capsid (protein shell of a virus), we performed Brownian dynamics simulations of the self-assembly of amphiphilic truncated cone particles with anisotropic interactions.

Complement components as promoters of immunological tolerance in dendritic cells

Complement and dendritic cells (DCs) share many functional features that drive the outcome of immune-inflammatory processes. Both have a sentinel function, acting as danger sensors specialized for a rapid, comprehensive and selective action against potential threats without damaging the healthy host cells. But while complement has been considered as a "master alarm" system poised for direct pathogen killing, DCs are regarded as "master regulators" or orchestrators of a vast range of effector immune cells for an effective immune response against threatening insults. The original definition of the complement system, coined to denote its auxiliary function to enhance or assist in the role of antibodies or phagocytes to clear microbes or damaged cells, envisaged an important crosstalk between the complement and the mononuclear phagocyte systems. More recent studies have shown that, depending on the microenvironmental conditions, several complement effectors are competent to influence the differentiation and/or function of different DC subsets toward immunogenicity or tolerance. In this review we will infer about the capability of complement activators and inhibitors to "condition" a tolerogenic and anti-inflammatory immune response by direct interaction with DC surface receptors, and about the implications of this knowledge to devise new complement-based therapeutic approaches for autoimmune pathologies.

Rational design of new materials using recombinant structural proteins: Current state and future challenges

Sequence-definable polymers are seen as a prerequisite for design of future materials, with many polymer scientists regarding such polymers as the holy grail of polymer science. Recombinant proteins are sequence-defined polymers. Proteins are dictated by DNA templates and therefore the sequence of amino acids in a protein is defined, and molecular biology provides tools that allow redesign of the DNA as required. Despite this advantage, proteins are underrepresented in materials science. In this publication we investigate the advantages and limitations of using proteins as templates for rational design of new materials.

Engineering Globular Protein Vesicles through Tunable Self-Assembly of Recombinant Fusion Proteins

Vesicles assembled from folded, globular proteins have potential for functions different from traditional lipid or polymeric vesicles. However, they also present challenges in understanding the assembly process and controlling vesicle properties. From detailed investigation of the assembly behavior of recombinant fusion proteins, this work reports a simple strategy to engineer protein vesicles containing functional, globular domains. This is achieved through tunable self-assembly of recombinant globular fusion proteins containing leucine zippers and elastin-like polypeptides. The fusion proteins form complexes in solution via high affinity binding of the zippers, and transition through dynamic coacervates to stable hollow vesicles upon warming. The thermal driving force, which can be tuned by protein concentration or temperature, controls both vesicle size and whether vesicles are single or bi-layered. These results provide critical information to engineer globular protein vesicles via self-assembly with desired size and membrane structure.

Homo- and heteropolymer self-assembly of recombinant trichocytic keratins

In the past two decades, keratin biomaterials have shown impressive results as scaffolds for tissue engineering, wound healing, and nerve regeneration. In addition to its intrinsic biocompatibility, keratin interacts with specific cell receptors eliciting beneficial biochemical cues. However, during extraction from natural sources, such as hair and wool fibers, natural keratins are subject to extensive processing conditions that lead to formation of unwanted by-products. Additionally, natural keratins suffer from limited sequence tunability. Recombinant keratin proteins can overcome these drawbacks while maintaining the desired chemical and physical characteristics of natural keratins. Herein, we present the bacterial expression, purification, and solution characterization of human hair keratins K31 and K81. The obligate heterodimerization of the K31/K81 pair that results in formation of intermediate filaments is maintained in the recombinant proteins. Surprisingly, we have for the first time observed new zero- and one-dimensional nanostructures from homooligomerization of K81 and K31, respectively. Further analysis of the self-assembly mechanism highlights the importance of disulfide crosslinking in keratin self-assembly.