The influence of digestive tract protein on cytotoxicity of polyvinyl chloride microplastics

Microplastics in food and drinking water can enter the human body through oral exposure, posing potential health risks to the human health. Most studies on the toxic effects of microplastics have focused on aquatic organisms, but the effects of the human digestive environment on the physicochemical properties of microplastics and their potential toxicity during gastrointestinal digestion are often limited. In this study, we first studied the influence of interactions between digestive tract protein (α-amylase, pepsin, and trypsin) and microplastics on the activity and conformation of digestive enzymes, and the physicochemical properties of polyvinyl chloride microplastics (PVC-MPs). Subsequently, a simulated digestion assay was performed to determine the biotransformation of PVC-MPs in the digestive tract and the intestinal toxicity of PVC-MPs. The in vitro experiments showed that the protein structure and activity of digestive enzymes were changed after adsorption by microplastics. After digestion, the static contact angle of PVC-MPs was decreased, indicating that the hydrophilicity of the PVC-MPs increased, which will increase its mobility in organisms. Cell experiment showed that the altered physicochemical property of PVC-MPs after digestion process also affect its cytotoxicity, including cellular uptake, cell viability, cell membrane integrity, reactive oxygen species levels, and mitochondrial membrane potential. Transcriptome analyses further confirmed the enhanced biotoxic effect of PVC-MPs after digestion treatment. Therefore, the ecological risk of microplastics may be underestimated owing to the interactions of microplastics and digestive tract protein during biological ingestion.

Hybrid Micro-/Nanoprotein Platform Provides Endocrine-like and Extracellular Matrix-like Cell Delivery of Growth Factors

Protein materials are versatile tools in diverse biomedical fields. Among them, artificial secretory granules (SGs), mimicking those from the endocrine system, act as mechanically stable reservoirs for the sustained release of proteins as oligomeric functional nanoparticles. Only validated in oncology, the physicochemical properties of SGs, along with their combined drug-releasing and scaffolding abilities, make them suitable as smart topographies in regenerative medicine for the prolonged delivery of growth factors (GFs). Thus, considering the need for novel, safe, and cost-effective materials to present GFs, in this study, we aimed to biofabricate a protein platform combining both endocrine-like and extracellular matrix fibronectin-derived (ECM-FN) systems. This approach is based on the sustained delivery of a nanostructured histidine-tagged version of human fibroblast growth factor 2. The GF is presented onto polymeric surfaces, interacting with FN to spontaneously generate nanonetworks that absorb and present the GF in the solid state, to modulate mesenchymal stromal cell (MSC) behavior. The results show that SGs-based topographies trigger high rates of MSCs proliferation while preventing differentiation. While this could be useful in cell therapy manufacture demanding large numbers of unspecialized MSCs, it fully validates the hybrid platform as a convenient setup for the design of biologically active hybrid surfaces and in tissue engineering for the controlled manipulation of mammalian cell growth.

Regulation of Peptide Liquid-Liquid Phase Separation by Aromatic Amino Acid Composition

Membraneless organelles are cellular biomolecular condensates that are formed by liquid-liquid phase separation (LLPS) of proteins and nucleic acids. LLPS is driven by multiple weak attractive forces, including intermolecular interactions mediated by aromatic amino acids. Considering the contribution of π-electron bearing side chains to protein-RNA LLPS, systematically study sought to how the composition of aromatic amino acids affects the formation of heterotypic condensates and their physical properties. For this, a library of minimalistic peptide building blocks is designed containing varying number and compositions of aromatic amino acids. It is shown that the number of aromatics in the peptide sequence affect LLPS propensity, material properties and (bio)chemical stability of peptide/RNA heterotypic condensates. The findings shed light on the contribution of aromatics' composition to the formation of heterotypic condensates. These insights can be applied for regulation of condensate material properties and improvement of their (bio)chemical stability, for various biomedical and biotechnological applications.

Genetically Fusing Order-Promoting and Thermoresponsive Building Blocks to Design Hybrid Biomaterials

The unique biophysical and biochemical properties of intrinsically disordered proteins (IDPs) and their recombinant derivatives, intrinsically disordered protein polymers (IDPPs) offer opportunities for producing multistimuli-responsive materials; their sequence-encoded disorder and tendency for phase separation facilitate the development of multifunctional materials. This review highlights the strategies for enhancing the structural diversity of elastin-like polypeptides (ELPs) and resilin-like polypeptides (RLPs), and their self-assembled structures via genetic fusion to ordered motifs such as helical or beta sheet domains. In particular, this review describes approaches that harness the synergistic interplay between order-promoting and thermoresponsive building blocks to design hybrid biomaterials, resulting in well-structured, stimuli-responsive supramolecular materials ordered on the nanoscale.

Tuning Supramolecular Chirality in Iodinated Amphiphilic Peptides Through Tripeptide Linker Editing

Protease-cleavable supramolecular oligopeptide nanofilaments are promising materials for targeted therapeutics and diagnostics. In these systems, single amino acid substitutions can have profound effects on the supramolecular structure and consequent proteolytic degradation, which are critical parameters for their intended applications. Herein, we describe changes to the self-assembly and proteolytic cleavage of iodine containing sequences for future translation into matrix metalloprotease (MMP-9)-activated supramolecular radio-imaging probes. We use a systematic single amino acid exchange in the tripeptide linker region of these peptide amphiphiles to provide insights into the role of each residue in the supramolecular assemblies. These modifications resulted in dramatic changes in the nature of the assembled structures formed, including an unexpected chiral inversion. By using circular dichroism, atomic force microscopy, Fourier transform infrared spectroscopy, and molecular dynamics simulations, we found that the GD loop, a common motif in β-turn elements, induced a reversal of the chiral orientation of the assembled nanofibers. In addition to the impact on peptide packing and chirality, MMP-9-catalyzed hydrolysis was evaluated for the four peptides, with the β-sheet content found to be a stronger determinant of enzymatic hydrolysis than supramolecular chirality. These observations provide fundamental insights into the sequence design in protease cleavable amphiphilic peptides with the potential for radio-labeling and selective biomedical applications.

Genetically Fused Resilin-like Polypeptide-Coiled Coil Bundlemer Conjugates Exhibit Tunable Multistimuli-Responsiveness and Undergo Nanofibrillar Assembly

Peptide-based materials are diverse candidates for self-assembly into modularly designed and stimuli-responsive nanostructures with precisely tunable compositions. Here, we genetically fused computationally designed coiled coil-forming peptides to the N- and C-termini of compositionally distinct multistimuli-responsive resilin-like polypeptides (RLPs) of various lengths. The successful expression of these hybrid polypeptides in bacterial hosts was confirmed through techniques such as gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism spectroscopy and ultraviolet-visible turbidimetry demonstrated that despite the fusion of disparate structural and responsive units, the coiled coils remained stable in the hybrid polypeptides, and the sequence-encoded differences in thermoresponsive phase separation of the RLPs were preserved. Cryogenic transmission electron microscopy and coarse-grained modeling showed that after thermal annealing in solution, the hybrid polypeptides adopted a closed loop conformation and assembled into nanofibrils capable of further hierarchically organizing into cluster structures and ribbon-like structures mediated by the self-association tendency of the RLPs.

Contribution of the ELRs to the development of advanced in vitro models

Developing in vitro models that accurately mimic the microenvironment of biological structures or processes holds substantial promise for gaining insights into specific biological functions. In the field of tissue engineering and regenerative medicine, in vitro models able to capture the precise structural, topographical, and functional complexity of living tissues, prove to be valuable tools for comprehending disease mechanisms, assessing drug responses, and serving as alternatives or complements to animal testing. The choice of the right biomaterial and fabrication technique for the development of these in vitro models plays an important role in their functionality. In this sense, elastin-like recombinamers (ELRs) have emerged as an important tool for the fabrication of in vitro models overcoming the challenges encountered in natural and synthetic materials due to their intrinsic properties, such as phase transition behavior, tunable biological properties, viscoelasticity, and easy processability. In this review article, we will delve into the use of ELRs for molecular models of intrinsically disordered proteins (IDPs), as well as for the development of in vitro 3D models for regenerative medicine. The easy processability of the ELRs and their rational design has allowed their use for the development of spheroids and organoids, or bioinks for 3D bioprinting. Thus, incorporating ELRs into the toolkit of biomaterials used for the fabrication of in vitro models, represents a transformative step forward in improving the accuracy, efficiency, and functionality of these models, and opening up a wide range of possibilities in combination with advanced biofabrication techniques that remains to be explored.

High-precision targeting and destruction of cancer-associated PDGFR-β+ stromal fibroblasts through self-assembling, protein-only nanoparticles

The need for more effective and precision medicines for cancer has pushed the exploration of new materials appropriate for drug delivery and imaging, and alternative receptors for targeting. Among the most promising strategies, finding suitable cell surface receptors and targeting agents for cancer-associated platelet derived growth factor receptor β (PDGFR-β)+ stromal fibroblasts is highly appealing. As a neglected target, this cell type mechanically and biologically supports the growth, progression, and infiltration of solid tumors in non-small cell lung, breast, pancreatic, and colorectal cancers. We have developed a family of PDGFR-β-targeted nanoparticles based on biofabricated, self-assembling proteins, upon hierarchical and iterative selective processes starting from four initial candidates. The modular protein PDGFD-GFP-H6 is well produced in recombinant bacteria, resulting in structurally robust oligomeric particles that selectively penetrates into PDGFR-β+ stromal fibroblasts in a dose-dependent manner, by means of the PDGFR-β ligand PDGFD. Upon in vivo administration, these GFP-carrying protein nanoparticles precisely accumulate in tumor tissues and enlighten them for IVIS observation. When GFP is replaced by a microbial toxin, selective tumor tissue destruction is observed associated with a significant reduction in tumor volume growth. The presented data validate the PDGFR-β/PDGFD pair as a promising toolbox for targeted drug delivery in the tumor microenvironment and oligomeric protein nanoparticles as a powerful instrument to mediate highly selective biosafe targeting in cancer through non-cancer cells. STATEMENT OF SIGNIFICANCE: We have developed a transversal platform for nanoparticle-based drug delivery into cancer-associated fibroblasts. This is based on the engineered modular protein PDGFD-GFP-H6 that spontaneously self-assemble and selectively penetrates into PDGFR-β+ stromal fibroblasts in a dose-dependent manner, by means of the PDGFR-β ligand PDGFD. In vivo, these protein nanoparticles accumulate in tumor and when incorporating a microbial toxin, they destroy tumor tissues with a significant reduction in tumor volume, in absence of side toxicities. The data presented here validate the PDGFR-β/PDGFD pair as a fully versatile toolbox for targeted drug delivery in the tumor microenvironment intended as a synergistic treatment.

Modulating the optical properties of carbon dots by peptide condensates

Here, we utilized designed condensates formed by liquid-liquid phase separation (LLPS) of cationic and aromatic peptide to sequester tyrosine-based carbon dots (C-dots). The C-dots fluorescence is quenched and retrieved upon partitioning and release from condensates, allowing a spatial regulation of C-dots fluorescence which can be utilized for biosensing applications.

Biomimetic Extracellular Scaffolds by Microfluidic Superstructuring of Nanofibers

The extracellular matrix is a dynamic framework bearing chemical and morphological cues that support many cellular functions, and artificial analogs with well-defined chemistry are of great interest for biomedical applications. Herein, we describe hierarchical, extracellular-matrix-mimetic microgels, termed "superbundles" (SBs) composed of peptide amphiphile (PA) supramolecular nanofiber networks created using flow-focusing microfluidic devices. We explore the effects of altered flow rate ratio and PA concentration on the ability to create SBs and develop design rules for producing SBs with both cationic and anionic PA nanofibers and gelators. We demonstrate the morphological similarities of SBs to decellularized extracellular matrices and showcase their ability to encapsulate and retain proteinaceous cargos with a wide variety of isoelectric points. Finally, we demonstrate that the novel SB morphology does not affect the well-established biocompatibility of PA gels.

Sequence Context and Complex Hofmeister Salt Interactions Dictate Phase Separation Propensity of Resilin-like Polypeptides

Resilin is an elastic material found in insects with exceptional durability, resilience, and extensibility, making it a promising biomaterial for tissue engineering. The monomeric precursor, pro-resilin, undergoes thermo-responsive self-assembly through liquid-liquid phase separation (LLPS). Understanding the molecular details of this assembly process is critical to developing complex biomaterials. The present study investigates the interplay between the solvent, sequence syntax, structure, and dynamics in promoting LLPS of resilin-like-polypeptides (RLPs) derived from domains 1 and 3 of Drosophila melanogaster pro-resilin. NMR, UV-vis, and microscopy data demonstrate that while kosmotropic salts and low pH promote LLPS, the effects of chaotropic salts with increasing pH are more complex. Subtle variations between the repeating amino acid motifs of resilin domain 1 and domain 3 lead to significantly different salt and pH dependence of LLPS, with domain 3 sequence motifs more strongly favoring phase separation under most conditions. These findings provide new insight into the molecular drivers of RLP phase separation and the complex roles of both RLP sequence and solution composition in fine-tuning assembly conditions.

Protein scaffolds in human clinics

Fundamental clinical areas such as drug delivery and regenerative medicine require biocompatible materials as mechanically stable scaffolds or as nanoscale drug carriers. Among the wide set of emerging biomaterials, polypeptides offer enticing properties over alternative polymers, including full biocompatibility, biodegradability, precise interactivity, structural stability and conformational and functional versatility, all of them tunable by conventional protein engineering. However, proteins from non-human sources elicit immunotoxicities that might bottleneck further development and narrow their clinical applicability. In this context, selecting human proteins or developing humanized protein versions as building blocks is a strict demand to design non-immunogenic protein materials. We review here the expanding catalogue of human or humanized proteins tailored to execute different levels of scaffolding functions and how they can be engineered as self-assembling materials in form of oligomers, polymers or complex networks. In particular, we emphasize those that are under clinical development, revising their fields of applicability and how they have been adapted to offer, apart from mere mechanical support, highly refined functions and precise molecular interactions.

Peptide Amphiphile Hydrogels Based on Homoternary Cucurbit[8]uril Host-Guest Complexes

Supramolecular hydrogels based on peptide amphiphiles (PAs) are promising materials for tissue engineering and model extracellular matrixes for biological studies. While PA hydrogels are conventionally formed via electrostatic screening, new hydrogelation mechanisms might help to improve the design and functionality of these materials. Here, we present a host-guest-mediated PA hydrogelation method that relies on the formation of a host-guest homoternary complex with cucurbit[8]uril (CB[8]) and aromatic amino-acid-bearing PA nanofibers. As a result of the host-guest cross-linking between PA nanofibers, hierarchical morphologies and increased stiffness were found when host-guest-mediated PA hydrogels were compared to their ion-based equivalents. Additionally, both families of hydrogels exhibited similar biocompatibilities. These results demonstrate that CB[8]-mediated hydrogelation can be used as an alternative cross-linking method to upgrade the design of PA materials and extend their biomedical applications.

Exploiting the fundamentals of biological organization for the advancement of biofabrication

The field of biofabrication continues to progress, offering higher levels of spatial control, reproducibility, and functionality. However, we remain far from recapitulating what nature has achieved. Biological systems such as tissues and organs are assembled from the bottom-up through coordinated supramolecular and cellular processes that result in their remarkable structures and functionalities. In this perspective, we propose that incorporating such biological assembling mechanisms within fabrication techniques, offers an opportunity to push the boundaries of biofabrication. We dissect these mechanisms into distinct biological organization principles (BOPs) including self-assembly, compartmentalization, diffusion-reaction, disorder-to-order transitions, and out-of-equilibrium processes. We highlight recent work demonstrating the viability and potential of these approaches to enhance scalability, reproducibility, vascularization, and biomimicry; as well as current challenges to overcome.

Peptide-Based Supramolecular Systems Chemistry

Peptide-based supramolecular systems chemistry seeks to mimic the ability of life forms to use conserved sets of building blocks and chemical reactions to achieve a bewildering array of functions. Building on the design principles for short peptide-based nanomaterials with properties, such as self-assembly, recognition, catalysis, and actuation, are increasingly available. Peptide-based supramolecular systems chemistry is starting to address the far greater challenge of systems-level design to access complex functions that emerge when multiple reactions and interactions are coordinated and integrated. We discuss key features relevant to systems-level design, including regulating supramolecular order and disorder, development of active and adaptive systems by considering kinetic and thermodynamic design aspects and combinatorial dynamic covalent and noncovalent interactions. Finally, we discuss how structural and dynamic design concepts, including preorganization and induced fit, are critical to the ability to develop adaptive materials with adaptive and tunable photonic, electronic, and catalytic properties. Finally, we highlight examples where multiple features are combined, resulting in chemical systems and materials that display adaptive properties that cannot be achieved without this level of integration.

Application of Thermoresponsive Intrinsically Disordered Protein Polymers in Nanostructured and Microstructured Materials

Modulation of inter- and intramolecular interactions between bioinspired designer molecules can be harnessed for developing functional structures that mimic the complex hierarchical organization of multicomponent assemblies observed in nature. Furthermore, such multistimuli-responsive molecules offer orthogonal tunability for generating versatile multifunctional platforms via independent biochemical and biophysical cues. In this review, the remarkable physicochemical and mechanical properties of genetically engineered protein polymers derived from intrinsically disordered proteins, specifically elastin and resilin, are discussed. This review highlights emerging technologies which use them as building blocks in the fabrication of highly programmable structured biomaterials for applications in delivery of biotherapeutic cargo and regenerative medicine.

Developing Protein-Antitumoral Drug Nanoconjugates as Bifunctional Antimicrobial Agents

A novel concept about bifunctional antimicrobial drugs, based on self-assembling protein nanoparticles, has been evaluated here over two biofilm-forming pathogens, namely Pseudomonas aeruginosa and Staphylococcus aureus. Two structurally different antimicrobial peptides (GWH1 and PaDBS1R1) were engineered to form regular nanoparticles of around 35 nm, to which the small molecular weight drug Floxuridine was covalently conjugated. Both the assembled peptides and the chemical, a conventional cytotoxic drug used in oncotherapy, showed potent antimicrobial activities that were enhanced by the combination of both molecules in single pharmacological entities. Therefore, the resulting prototypes show promises as innovative nanomedicines, being potential alternatives to conventional antibiotics. The biological performance and easy fabrication of these materials fully support the design of protein-based hybrid constructs for combined molecular therapies, expected to have broad applicability beyond antimicrobial medicines. In addition, the approach taken here validates the functional exploration and repurposing of antitumoral drugs, which at low concentrations perform well as unexpected biofilm-inhibiting agents.

Heterotypic Supramolecular Hydrogels Formed by Noncovalent Interactions in Inflammasomes

The advance of structural biology has revealed numerous noncovalent interactions between peptide sequences in protein structures, but such information is less explored for developing peptide materials. Here we report the formation of heterotypic peptide hydrogels by the two binding motifs revealed by the structures of an inflammasome. Specifically, conjugating a self-assembling motif to the positively or negatively charged peptide sequence from the ASCPYD filaments of inflammasome produces the solutions of the peptides. The addition of the peptides of the oppositely charged and complementary peptides to the corresponding peptide solution produces the heterotypic hydrogels. Rheology measurement shows that ratios of the complementary peptides affect the viscoelasticity of the resulted hydrogel. Circular dichroism indicates that the addition of the complementary peptides results in electrostatic interactions that modulate self-assembly. Transmission electron microscopy reveals that the ratio of the complementary peptides controls the morphology of the heterotypic peptide assemblies. This work illustrates a rational, biomimetic approach that uses the structural information from the protein data base (PDB) for developing heterotypic peptide materials via self-assembly.