Impact of glycan nature on structure and viscoelastic properties of glycopeptide hydrogels

Mucus is a complex biological hydrogel that acts as a barrier for almost everything entering or exiting the body. It is therefore of emerging interest for biomedical and pharmaceutical applications. Besides water, the most abundant components are the large and densely glycosylated mucins, glycoproteins of up to 20 MDa and carbohydrate content of up to 80 wt%. Here, we designed and explored a library of glycosylated peptides to deconstruct the complexity of mucus. Using the well-characterized hFF03 coiled-coil system as a hydrogel-forming peptide scaffold, we systematically probed the contribution of single glycans to the secondary structure as well as the formation and viscoelastic properties of the resulting hydrogels. We show that glycan-decoration does not affect α-helix and coiled-coil formation while it alters gel stiffness. By using oscillatory macrorheology, dynamic light scattering microrheology, and fluorescence lifetime-based nanorheology, we characterized the glycopeptide materials over several length scales. Molecular simulations revealed that the glycosylated linker may extend into the solvent, but more frequently interacts with the peptide, thereby likely modifying the stability of the self-assembled fibers. This systematic study highlights the interplay between glycan structure and hydrogel properties and may guide the development of synthetic mucus mimetics.

Design and synthesis of a nucleobase functionalized peptide hydrogel: in vitro assessment of anti-inflammatory and wound healing effects

Over the past several years, a significant increase in the expanding field of biomaterial sciences has been observed due to the development of biocompatible materials based on peptide derivatives that have intrinsic therapeutic potential. In this report, we synthesized nucleobase functionalized peptide derivatives (NPs). Hydrogelation in the synthesized NPs was induced by increasing their hydrophobicity with an aromatic moiety. The aggregation behavior of the NPs was analyzed by performing molecular dynamics simulations and DOSY NMR experiments. We performed circular dichroism (CD), thioflavin-T binding and PXRD to characterize the supramolecular aggregation in the NP1 hydrogel. The mechanical strength of the NP1 hydrogel was tested by performing rheological experiments. TEM and SEM experiments were performed to investigate the morphology of the NP1 hydrogel. The biocompatibility of the newly synthesized NP1 hydrogel was investigated using McCoy and A549 cell lines. The hemolytic activity of the NP1 hydrogel was examined in human blood cells. The stability of the newly formed NP1 hydrogel was examined using proteinase K and α-chymotrypsin. The NP1 hydrogel was used for in vitro wound healing. Western blotting, qRT-PCR and DCFDA assay were performed to determine the anti-inflammatory activity of the NP1 hydrogel. The synthesized NP1 hydrogel also exhibits antibacterial efficacy.

Viscoelastic Supramolecular Hyaluronan-Peptide Cross-Linked Hydrogels

Viscoelasticity plays a key role in hydrogel design. We designed a physically cross-linked hydrogel with tunable viscoelasticity, comprising supramolecular-assembled peptides coupled to hyaluronan (HA), a native extracellular matrix component. We then explored the structural and molecular mechanisms underlying the mechanical properties of a series of these HA-peptide hydrogels. By modifying the peptide sequence, we modulated both long- and short-time stress relaxation rates as a way to target viscoelasticity with limited impact on stiffness, leading to gels that relax up to 60% of stress in 10 min. Gels with the highest viscoelasticity exhibited large mesh sizes and β-sheet secondary structures. The stiffness of the gel correlated with hydrogen bonding between the peptide chains. These gels are cytocompatible: highly viscoelastic gels that mimic the native skin microenvironment promote dermal fibroblast cell spreading. Moreover, HA-peptide gels enabled cell encapsulation, as shown with primary human T cells. Overall, these physically-cross-linked hydrogels enable tunable viscoelasticity that can be used to modulate cell morphology.

Self-assembled peptide hydrogels for the treatment of diabetes and associated complications

Diabetes is a widespread epidemic that includes a number of comorbid conditions that greatly increase the chance of acquiring other chronic illnesses. Every year, there are significantly more people with diabetes because of the rise in type-2 diabetes prevalence. The primary causes of illness and mortality worldwide are, among these, hyperglycemia and its comorbidities. There has been a lot of interest in the creation of peptide-based hydrogels as a potentially effective platform for the treatment of diabetes and its consequences. Here, we emphasize the use of self-assembled hydrogel formulations and their unique potential for the treatment/management of type-2 diabetes and its consequences. (i.e., wounds). Key aspects covered include the characteristics of self-assembled peptide hydrogels, methods for their preparation, and their pre-clinical and clinical applications in addressing metabolic disorders such as type-2 diabetes.

How Chromophore Labels Shape the Structure and Dynamics of a Peptide Hydrogel

Biocompatible and functionalizable hydrogels have a wide range of (potential) medicinal applications. The hydrogelation process, particularly for systems with very low polymer weight percentages (<1 wt %), remains poorly understood, making it challenging to predict the self-assembly of a given molecular building block into a hydrogel. This severely hinders the rational design of self-assembled hydrogels. In this study, we demonstrate the impact of an N-terminal group on the self-assembly and rheology of the peptide hydrogel hFF03 (hydrogelating, fibril forming peptide 03) using molecular dynamics simulations, oscillatory shear rheology, and circular dichroism spectroscopy. We find that the chromophore and even its specific regioisomers have a significant influence on the microscopic structure and dynamics of the self-assembled fibril, and on the macroscopic mechanical properties. This is because the chromophore influences the possible salt bridges, which form and stabilize the fibril formation. Furthermore, we find that the solvation shell fibrils by itself cannot explain the viscoelasticity of hFF03 hydrogels. Our atomistic model of the hFF03 fibril formation enables a more rational design of these hydrogels. In particular, altering the N-terminal chromophore emerges as a design strategy to tune the mechanic properties of these self-assembled peptide hydrogels.

Mechanisms and influencing factors of peptide hydrogel formation and biomedicine applications of hydrogels

Self-assembled peptide-based hydrogels have shown great potential in bio-related applications due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization. Herein, the structure and characteristics of hydrogels and the mechanism of action of several regular secondary structures during gelation are investigated. The factors influencing the formation of peptide hydrogels, especially the pH responsiveness and salt ion induction are analyzed and summarized. Finally, the biomedical applications of peptide hydrogels, such as bone tissue engineering, cell culture, antigen presentation, antibacterial materials, and drug delivery are reviewed.

Osmolytes Modulate Photoactivation of Phytochrome: Probing Protein Hydration

Phytochromes are bistable red/far-red light-responsive photoreceptor proteins found in plants, fungi, and bacteria. Light-activation of the prototypical phytochrome Cph1 from the cyanobacterium Synechocystis sp. PCC 6803 allows photoisomerization of the bilin chromophore in the photosensory module and a subsequent series of intermediate states leading from the red absorbing Pr to the far-red-absorbing Pfr state. We show here via osmotic and hydrostatic pressure-based measurements that hydration of the photoreceptor modulates the photoconversion kinetics in a controlled manner. While small osmolytes like sucrose accelerate Pfr formation, large polymer osmolytes like PEG 4000 delay the formation of Pfr. Thus, we hypothesize that an influx of mobile water into the photosensory domain is necessary for proceeding to the Pfr state. We suggest that protein hydration changes are a molecular event that occurs during photoconversion to Pfr, in addition to light activation, ultrafast electric field changes, photoisomerization, proton release and uptake, and the major conformational change leading to signal transmission, or simultaneously with one of these events. Moreover, we discuss this finding in light of the use of Cph1-PGP as a hydration sensor, e.g., for the characterization of novel hydrogel biomaterials.

Mismatched covalent and noncovalent templating leads to large coiled coil-templated macrocycles

Herein we describe the use of dynamic combinatorial chemistry to self-assemble complex coiled coil motifs. We amide-coupled a series of peptides designed to form homodimeric coiled coils with 3,5-dithiobenzoic acid (B) at the N-terminus and then allowed each B-peptide to undergo disulfide exchange. In the absence of peptide, monomer B forms cyclic trimers and tetramers, and thus we expected that addition of the peptide to monomer B would shift the equilibrium towards the tetramer to maximize coiled coil formation. Unexpectedly, we found that internal templation of the B-peptide through coiled coil formation shifts the equilibrium towards larger macrocycles up to 13 B-peptide subunits, with a preference for 4, 7, and 10-membered macrocycles. These macrocyclic assemblies display greater helicity and thermal stability relative to intermolecular coiled coil homodimer controls. The preference for large macrocycles is driven by the strength of the coiled coil, as increasing the coiled coil affinity increases the fraction of larger macrocycles. This system represents a new approach towards the development of complex peptide and protein assemblies.

Peptide-Based Supramolecular Hydrogels as Drug Delivery Agents: Recent Advances

Supramolecular peptide hydrogels have many important applications in biomedicine, including drug delivery applications for the sustained release of therapeutic molecules. Targeted and selective drug administration is often preferential to systemic drug delivery, as it can allow reduced doses and can avoid the toxicity and side-effects caused by off-target binding. New discoveries are continually being reported in this rapidly developing field. In this review, we report the latest developments in supramolecular peptide-based hydrogels for drug delivery, focusing primarily on discoveries that have been reported in the last four years (2018-present). We address clinical points, such as peptide self-assembly and drug release, mechanical properties in drug delivery, peptide functionalization, bioadhesive properties and drug delivery enhancement strategies, drug release profiles, and different hydrogel matrices for anticancer drug loading and release.

Rational design of amphiphilic fluorinated peptides: evaluation of self-assembly properties and hydrogel formation

Advanced peptide-based nanomaterials composed of self-assembling peptides (SAPs) are of emerging interest in pharmaceutical and biomedical applications. The introduction of fluorine into peptides, in fact, offers unique opportunities to tune their biophysical properties and intermolecular interactions. In particular, the degree of fluorination plays a crucial role in peptide engineering as it can be used to control the characteristics of fluorine-specific interactions and, thus, peptide conformation and self-assembly. Here, we designed and explored a series of amphipathic peptides by incorporating the fluorinated amino acids (2S)-4-monofluoroethylglycine (MfeGly), (2S)-4,4-difluoroethylglycine (DfeGly) and (2S)-4,4,4-trifluoroethylglycine (TfeGly) as hydrophobic components. This approach enabled studying the impact of fluorination on secondary structure formation and peptide self-assembly on a systematic basis. We show that the interplay between polarity and hydrophobicity, both induced differentially by varying degrees of side chain fluorination, does affect peptide folding significantly. A greater degree of fluorination promotes peptide fibrillation and subsequent formation of physical hydrogels in physiological conditions. Molecular simulations revealed the key role played by electrostatically driven intra-chain and inter-chain contact pairs that are modulated by side chain fluorination and give insights into the different self-organization behaviour of selected peptides. Our study provides a systematic report about the distinct features of fluorinated oligomeric peptides with potential applications as peptide-based biomaterials.

Fabrication of a Tailored, Hybrid Extracellular Matrix Composite

The extracellular matrix (ECM) is a network of connective fibers that supports cells living in their surroundings. Native ECM, generated by the secretory products of each tissue's resident cells, has a unique architecture with different protein composition depending on the tissue. Therefore, it is very difficult to artificially design in vivo architecture in tissue engineering. In this study, we fabricated a hybrid ECM scaffold from the basic structure of fibroblast-derived cellular ECMs by adding major ECM components of fibronectin (FN) and collagen (COL I) externally. It was confirmed that while maintaining the basic structure of the native ECM, major protein components can be regulated. Then, decellularization was performed to prepare hybrid ECM scaffolds with various protein compositions and we demonstrated that a liver-mimicking fibronectin (FN)-rich hybrid ECM promoted successful settling of H4IIE rat hepatoma cells. We believe that our method holds promise for the fabrication of scaffolds that provide a tailored cellular microenvironment for specific organs and serve as novel pathways for the replacement or regeneration of specific organ tissues. This article is protected by copyright. All rights reserved.