Zinc(II)–Histidine Induced Collagen Peptide Assemblies: Morphology Modulation and Hydrolytic Catalysis Evaluation

Carbohydrate Co-Solutes Stabilize Collagen Triple Helices

Carbohydrates are common co-solutes for the stabilization of proteins. The effect of carbohydrate solutions on the stability of collagen, the most abundant protein in mammals, is, however, underexplored. In this work, we studied the thermal stability of collagen triple helices derived from a molecularly defined collagen model peptide (CMP), Ac-(Pro-Hyp-Gly)7 -NH2 , in solutions of six common mono- and disaccharides. We show that the carbohydrates stabilize the collagen triple helix in a concentration-dependent manner, with an increase of the melting temperature of up to 17 °C. In addition, we show that the stabilizing effect is similar for all studied sugars, including trehalose, which is otherwise considered a privileged bioprotectant. The results provided insight into the effects of sugar co-solutes on collagen triple helices and can aid the selection of storage environments for collagen-based materials and probes.

Genetically encoded zinc-binding collagen-like protein hybrid hydrogels for wound repair

Incorporating zinc oxide nanoparticles (ZnOnps) into collagen is a promising strategy for fabricating biomaterials with excellent antibacterial activity, but modifications are necessary due to the low zinc binding affinity of native collagen, which can cause disturbances to the functions of both ZnOnps and collagen and result in heterogeneous effects. To address this issue, we have developed a genetically encoded zinc-binding collagen-like protein, Zn-eCLP3, which was genetically modified by Scl2 collagen-like protein. Our study found that Zn-eCLP3 has a binding affinity for zinc that is 3-fold higher than that of commercialized type I collagen, as determined by isothermal titration calorimetry (ITC). Using ZnOnps-coordinated Zn-eCLP3 protein and xanthan gum, we prepared a hydrogel that showed significantly stronger antibacterial activity compared to a collagen hydrogel prepared in the same manner. In vitro cytocompatibility tests were conducted to assess the potential of the Zn-eCLP3 hydrogel for wound repair applications. In vivo experiments, which involved an S. aureus-infected mouse trauma model, showed that the application of the Zn-eCLP3 hydrogel resulted in rapid wound regeneration and increased expression of collagen-1α and cytokeratin-14. Our study highlights the potential of Zn-eCLP3 and the hybrid hydrogel for further studies and applications in wound repair.

Tannin-Assisted Synthesis of Nanocomposites Loaded with Silver Nanoparticles and Their Multifunctional Applications

Nanocomposites have been widely used in many important areas due to their particular physical/chemical properties; however, just though a simple technology, endowing multiple functions into a single nanomaterial for realizing their multifunctional applications is still a challenge. Here, we report a robust method for the facile synthesis of Ag-based multifunctional nanocomposites via using tannin-coated phenol-formaldehyde resin nanospheres (TA-PFRN) as silver nanoparticle (Ag NP) carriers. The thickness of the tannin coating is readily tuned from 50 to 320 nm by regulating the concentration of tannin added. Under the optimal conditions, the TA-PFRN has a 23.8 wt % of Ag NPs loading capacity with only 17.2 nm Ag NP layers. Consequently, the novel TA-PFRN@Ag nanocomposites possess multiple functions and integrated characteristics. As catalysts, the catalytic efficiency of TA-PFRN@Ag is nearly 6 times higher than that of the PFRN@Ag. As highly effective free radical initiators, TA-PFRN@Ag nanocomposites can trigger ultrafast acrylic acid (AA)/acrylamide (AM) polymerization at room temperature (in only a few minutes). As nano-reinforced fillers, the addition of 0.04 wt % nanocomposites can improve the tensile strength of PVA film from 60 to 153.2 MPa. In addition, the nanocomposites can also serve as antibacterial agents, efficiently inhibiting the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus); as antiultraviolet agents, the presence of TA-PFRN@Ag nanocomposites endows the film/hydrogel materials excellent ultraviolet (UV) shielding. This work provides a novel strategy for the green synthesis of Ag-based multifunctional nanocomposites that show promising applications in catalysis, nanomaterials, and biomedicine.

Injectable Sealants Based on Silk Fibroin for Fast Hemostasis and Wound Repairing

Uncontrollable blood loss poses fatality risks and most recently developed sealants still share common limitations on controversial components, degradability, mechanical strength or gelation time. Herein, series of injectable sealants based on silk fibroin (SF) is developed. Random coil/β-sheet conformation transition in SF is achieved by forming dendritic intermediates under induction of the structurally compatible and chemically complementary assembly peptide (Ac-KAEA-KAEA-KAEA-KAEA-NH2 , KA16 ). A ratio of 1:5 (KA-SF-15) shown an accelerating gelation process (≈12 s) and enhanced mechanical strength at physiological conditions. The interweaved nanofibers effectively impeded the bleeding within 30 s and no obvious adverse effects are observed. The supramolecular interactions and in vivo degradation benefit the inflammatory host cells infiltration and cytokines diffusion. Without any exogenous factors, the increased expression of VEGF and PDGF led to a positive feedback regulation on fibroblasts and vascular endothelial cell growth/proliferation and promoted the wound healing. These findings indicated the few assembly-peptide can accelerate fibroin gelation transition at a limited physiological condition, and the injectable amino acid-based sealants show obvious advantages on biocompatibility, degradability, rapid gelation and matched strength, with strong potential to act as next generation of biomedical materials.

Predicting Collagen Triple Helix Stability through Additive Effects of Terminal Residues and Caps

Collagen model peptides (CMPs) consisting of proline-(2S,4R)-hydroxyproline-glycine (POG) repeats have provided a breadth of knowledge of the triple helical structure of collagen, the most abundant protein in mammals. Predictive tools for triple helix stability have, however, lagged behind since the effect of CMPs with different frames ([POG]_n , [OGP]_n , or [GPO]_n ) and capped or uncapped termini have so far been underestimated. Here, we elucidated the impact of the frame, terminal functional group and its charge on the stability of collagen triple helices. Combined experimental and theoretical studies with frame-shifted, capped and uncapped CMPs revealed that electrostatic interactions, strand preorganization, interstrand H-bonding, and steric repulsion at the termini contribute to triple helix stability. We show that these individual contributions are additive and allow for the prediction of the melting temperatures of CMP trimers.

Frame Shifts Affect the Stability of Collagen Triple Helices

Collagen model peptides (CMPs), composed of proline-(2S,4R)-hydroxyproline-glycine (POG) repeat units, have been extensively used to study the structure and stability of triple-helical collagen─the dominant structural protein in mammals─at the molecular level. Despite the more than 50-year history of CMPs and numerous studies on the relationship between the composition of single-stranded CMPs and the thermal stability of the assembled triple helices, little attention has been paid to the effects arising from their terminal residues. Here, we show that frame-shifted CMPs, which share POG repeat units but terminate with P, O, or G, form triple helices with vastly different thermal stabilities. A melting temperature difference as high as 16 °C was found for triple helices from 20-mers Ac-OG[POG]₆-NH₂ and Ac-[POG]₆PO-NH₂, and triple helices of the constitutional isomers Ac-[POG]₇-NH₂ and Ac-[GPO]₇-NH₂ melt 10 °C apart. A combination of thermal denaturation, circular dichroism and NMR spectroscopic studies, and molecular dynamics simulations revealed that the stability differences originate from the propensity of the peptide termini to preorganize into a polyproline-II helical structure. Our results advise that care must be taken when designing peptide mimics of structural proteins, as subtle changes in the terminal residues can significantly affect their properties. Our findings also provide a general and straightforward tool for tuning the stability of CMPs for applications as synthetic materials and biological probes.

A rethinking of collagen as tough biomaterials in meat packaging: assembly from native to synthetic

Due to the high moisture-associated typical rheology and the changeable and harsh processing conditions in the production process, packaging materials for meat products have higher requirements including a sufficient mechanical strength and proper ductility. Collagen, a highly conserved structural protein consisting of a triple helix of Gly-X-Y repeats, has been proved to be suitable packaging material for meat products. The treated animal digestive tract (i.e. the casing) is the perfect natural packaging material for wrapping meat into sausage. Its thin walls, strong toughness and impact resistance make it the oldest and best edible meat packaging. Collagen casing is another wisdom of meat packaging, which is made by collagen fibers from hide skin, presenting a rapid growth in casing market. To strengthen mechanical strength and barrier behaviors of collagen-based packaging materials, different physical, chemical, and biological cross-linking methods are springing up exuberantly, as well as a variety of reinforcement approaches including nanotechnology. In addition, the rapid development of biomimetic technology also provides a good research idea and means for the promotion of collagen's assembly and relevant mechanical properties. This review can offer some reference on fundamental theory and practical application of collagenous materials in meat products.

Biomaterial functionalization with triple-helical peptides for tissue engineering

In the growing field of tissue engineering, providing cells in biomaterials with the adequate biological cues represents an increasingly important challenge. Yet, biomaterials with excellent mechanical properties often are often biologically inert to many cell types. To address this issue, researchers resort to functionalization, i.e. the surface modification of a biomaterial with active molecules or substances. Functionalization notably aims to replicate the native cellular microenvironment provided by the extracellular matrix, and in particular by collagen, its major component. As our understanding of biological processes regulating cell behaviour increases, functionalization with biomolecules binding cell surface receptors constitutes a promising strategy. Amongst these, triple-helical peptides (THPs) that reproduce the architectural and biological properties of collagen are especially attractive. Indeed, THPs containing binding sites from the native collagen sequence have successfully been used to guide cell response by establishing cell-biomaterial interactions. Notably, the GFOGER motif recognising the collagen-binding integrins is extensively employed as a cell adhesive peptide. In biomaterials, THPs efficiently improved cell adhesion, differentiation and function on biomaterials designed for tissue repair (especially for bone, cartilage, tendon and heart), vascular graft fabrication, wound dressing, drug delivery or immunomodulation. This review describes the key characteristics of THPs, their effect on cells when combined to biomaterials and their strong potential as biomimetic tools for regenerative medicine. STATEMENT OF SIGNIFICANCE: This review article describes how triple-helical peptides constitute efficient tools to improve cell-biomaterial interactions in tissue engineering. Triple helical peptides are bioactive molecules that mimic the architectural and biological properties of collagen. They have been successfully used to specifically recognize cell-surface receptors and provide cells seeded on biomaterials with controlled biological cues. Functionalization with triple-helical peptides has enabled researchers to improve cell function for regenerative medicine applications, such as tissue repair. However, despite encouraging results, this approach remains limited and under-exploited, and most functionalization strategies reported in the literature rely on biomolecules that are unable to address collagen-binding receptors. This review will assist researchers in selecting the correct tools to functionalize biomaterials in efforts to guide cellular response.

Supramolecular assembly of protein building blocks: from folding to function

Several phenomena occurring throughout the life of living things start and end with proteins. Various proteins form one complex structure to control detailed reactions. In contrast, one protein forms various structures and implements other biological phenomena depending on the situation. The basic principle that forms these hierarchical structures is protein self-assembly. A single building block is sufficient to create homogeneous structures with complex shapes, such as rings, filaments, or containers. These assemblies are widely used in biology as they enable multivalent binding, ultra-sensitive regulation, and compartmentalization. Moreover, with advances in the computational design of protein folding and protein-protein interfaces, considerable progress has recently been made in the de novo design of protein assemblies. Our review presents a description of the components of supramolecular protein assembly and their application in understanding biological phenomena to therapeutics.

Formation of Microcages from a Collagen Mimetic Peptide via Metal-Ligand Interactions

Here, the hierarchical assembly of a collagen mimetic peptide (CMP) displaying four bipyridine moieties is described. The CMP was capable of forming triple helices followed by self-assembly into disks and domes. Treatment of these disks and domes with metal ions such as Fe(II), Cu(II), Zn(II), Co(II), and Ru(III) triggered the formation of microcages, and micron-sized cup-like structures. Mechanistic studies suggest that the formation of the microcages proceeds from the disks and domes in a metal-dependent fashion. Fluorescently-labeled dextrans were encapsulated within the cages and displayed a time-dependent release using thermal conditions.

Tripeptide Self-Assembly into Bioactive Hydrogels: Effects of Terminus Modification on Biocatalysis

Bioactive hydrogels based on the self-assembly of tripeptides have attracted great interest in recent years. In particular, the search is active for sequences that are able to mimic enzymes when they are self-organized in a nanostructured hydrogel, so as to provide a smart catalytic (bio)material whose activity can be switched on/off with assembly/disassembly. Within the diverse enzymes that have been targeted for mimicry, hydrolases find wide application in biomaterials, ranging from their use to convert prodrugs into active compounds to their ability to work in reverse and catalyze a plethora of reactions. We recently reported the minimalistic l-His-d-Phe-d-Phe for its ability to self-organize into thermoreversible and biocatalytic hydrogels for esterase mimicry. In this work, we analyze the effects of terminus modifications that mimic the inclusion of the tripeptide in a longer sequence. Therefore, three analogues, i.e., N-acetylated, C-amidated, or both, were synthesized, purified, characterized by several techniques, and probed for self-assembly, hydrogelation, and esterase-like biocatalysis. This work provides useful insights into how chemical modifications at the termini affect self-assembly into biocatalytic hydrogels, and these data may become useful for the future design of supramolecular catalysts for enhanced performance.

Thermoresponsive Hemostatic Hydrogel with a Biomimetic Nanostructure Constructed from Aggregated Collagen Nanofibers

Uncontrollable bleeding poses considerable fatality risks by large-volume blood losses. Current emergency antibleeding handlings including either compression with gauze or "passive" blood transfusion are thus far from ideal, while most recently developed hemostatic agents still share common limitations without considering the subsequent tissue repairing and antibacterial activity after treatment. Herein, we introduce a novel bioinspired aggregated collagen nanofiber-based biocompatible and efficient hemostatic hydrogel material (TS-Gel-Ag-col) prepared by the integration of multifunctional compounds of muco-mimetic poloxamer, polyvinylpyrrolidone, and dencichine/chitosan dialdehyde synergistic crosslinked aggregated collagen nanofibers decorated with silver nanoparticles. Comprehensive material characterization and in vitro and in vivo studies of TS-Gel-Ag-col demonstrate that these materials possess effective antihemorrhagic and antibacterial wound protection effects. Moreover, TS-Gel-Ag-col can facilitate the tissue repairing of skin wounds by promoting revascularization. TS-Gel-Ag-col holds great promise for next-generation collagen-based absorbable hemostatic materials and for the development of smart artificial skins.

Intrinsic Role of Molecular Architectonics in Enhancing the Catalytic Activity of Lead in Glucose Hydrolysis

Lewis acidity plays a key role in the catalytic activity of lead ion (Pb^II) in the hydrolysis of glucose in solution under harsh synthetic conditions. We report a number of structurally similar d-gluconamide amphiphiles as functional organic ligands with active an -NH center capable of coordinating Pb^II (viz., Pb^II-N-C) in basic condition to enhance the catalytic efficiency through the scheme of molecular architectonics. Amphiphiles with different hydrophobic unit form assembly-architectures with a varying second coordination sphere around the active metal ion center. As a result, the active Pb^II center in each architecture exhibits substantially different efficiency toward catalyzing the glucose hydrolysis under ambient temperature. The catalytic performance of the dynamic and reversible gluconamide-Pb^II assembly-architectures are highly dependent on their chemical environments in solution. Further, the active Pb^II center of gluconamide-Pb^II complex in the assembly architecture and dispersed states exhibits distinct outcomes with the former being a superior catalyst than the latter as well as Pb^II alone. The current study demonstrates the potential of molecular architectonics that relies on the hydrophobic units of designer functional amphiphiles to enrich surface electron density with enhanced σ-donation ability through space which substantially improves the catalytic efficiency of Pb^II toward glucose hydrolysis at ambient temperature.

Conjugating Catalytic Polyproline Fragments with a Self-Assembling Peptide Produces Efficient Artificial Hydrolases

A polyproline fragment containing a catalytic dyad of His-His or Ser-His was coupled with a self-assembling peptide MAX1 to design new hydrolases (H2H5 and H2S5) for catalyzing ester hydrolysis. Circular dichroism measurements indicated that the peptides change their conformation from random coils to β-sheets when pH increases from 5 to 10. IR spectra also displayed the vibration modes corresponding to their β-structures at pH 9.0. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements showed that in solution, the designed peptides self-assemble into network fibrils having a significantly increased catalytic efficiency on ester hydrolysis. On p-nitrophenyl acetate (p-NPA) substrate, the designed peptides exhibit high catalytic efficiency at pH 9.0 (k_cat/K_M = 12.1 M^-1 s^-1 for H2H5, 13.3 M^-1 s^-1 for H2S5), and their efficiency is even better at pH 10.0 (k_cat/K_M = 24.3 M^-1 s^-1 for H2H5, 99.4 M^-1 s^-1 for H2S5). Additionally, H2H5 and H2S5 also display good activity on catalyzing the hydrolysis of p-nitrophenyl-(2-phenyl)-propanoate (p-NPP) and p-nitrophenyl methoxyacetate (p-NPMA). Combining the polyproline-based catalytic scaffold with a self-assembling peptide generates an efficient hydrolase, providing a new design for effective artificial enzymes.

Development of a novel bio-inspired "cotton-like" collagen aggregate/chitin based biomaterial with a biomimetic 3D microstructure for efficient hemostasis and tissue repair

Hemostatic materials based on collagen and chitin are commonly assessed with regard to their topical absorbability and bioactivity. However, their clinical application faces challenges such as relatively long hemostatic and wound healing times, single function, as well as wound bleeding in patients with blood diseases. Herein, a novel bio-inspired "cotton-like" collagen aggregate/chitin based biomaterial for rapid hemostatic and tissue repair (V-3D-Ag-col) was fabricated by a specific gradient-removal solvent approach. Significantly, for the first time, an advanced collagen aggregate (Ag-col) composed of typical D-periodic cross-striated collagen fibrils and thick collagen fiber bundles was used instead of traditional collagen molecules (Col) to construct a hemostatic material. The target material showed a biomimetic 3D microstructure and "cotton-like" appearance, as expected, which were conducive to platelet adhesion and aggregation. The fabricated V-3D-Ag-col exhibited superior thermo-stability, hemostatic activity and biodegradability. More importantly, V-3D-Ag-col could significantly promote cell growth and proliferation. Further, V-3D-Ag-col could accelerate the wound healing process better than the same material based on conventional collagen (V-3D-Col). In consequence, V-3D-Ag-col has the potential to become a new generation of collagen-absorbable functional hemostatic materials. Furthermore, Ag-col can replace the currently available conventional collagen materials as raw materials for the new generation of collagen-based biomedical materials.

Luminescent Biofunctional Collagen Mimetic Nanofibers

Collagen has long been one of the top targets for biomimetic design due to its superior structural and functional properties. Significant progress has been achieved to construct self-assembling peptides to mimic the fibrous nanostructure of native collagen, while it is still very demanding to fabricate peptide assemblies that can recapitulate both structural and biofunctional features of collagen. Herein, collagen-like peptides have been synthesized to contain negatively charged amino acids as the binding groups of lanthanide ions and the integrin-binding motif GFOGER. The simultaneous inclusion of negatively charged amino acids in the middle as well as at both terminals drives the peptides to self-assemble to form well-ordered nanofibers with distinct periodic banding patterns specifically mediated by lanthanide ions. The aggregation tendency and the morphology of the final assembled materials for the peptides are modulated in a pH-cooperative manner, which well mimics the pH-dependent fibrillogenesis of Type I collagen. The utilization of lanthanide ions in the system not only offers a convenient external stimulus but also functionalizes assembled materials with excellent luminescent features. Most notably, the lanthanide-triggered peptide assembled nanomaterials possess good cell adhesion properties, which resemble the biological function of collagen. This peptide-Ln³⁺ system provides a facile and potent strategy to generate nanofibers that mimic both the structural and functional properties of natural collagen. These novel pH-responsive, luminescent, and biofunctional collagen mimetic nanofibers open fascinating opportunities in the development of improved functional biomaterials in tissue engineering, drug delivery, and medical diagnostics.