Design of Thermoresponsive Elastin-Like Glycopolypeptides for Selective Lectin Binding and Sorting

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.

Nanostructured multifunctional stimuli-responsive glycopolypeptide-based copolymers for biomedical applications

Inspired by natural resources, such as peptides and carbohydrates, glycopolypeptide biopolymer has recently emerged as a new form of biopolymer being recruited in various biomedical applications. Glycopolypeptides with well-defined secondary structures and pendant glycosides on the polypeptide backbone have sparked lots of research interest and they have an innate ability to self-assemble in diverse structures. The nanostructures of glycopolypeptides have also opened up new perspectives in biomedical applications due to their stable three-dimensional structures, high drug loading efficiency, excellent biocompatibility, and biodegradability. Although the development of glycopolypeptide-based nanocarriers is well-studied, their clinical translation is still limited. The present review highlights the preparation and characterization strategies related to glycopolypeptides-based copolymers, followed by a comprehensive discussion on their biomedical applications with a specific focus on drug delivery by various stimuli-responsive (e.g., pH, redox, conduction, and sugar) nanostructures, as well as their beneficial usage in diagnosis and regenerative medicine.

Mannose-based surfactant as biofunctional nanoemulsion stabilizer

The development and implementation of new amphiphiles based on natural resources rather than petrochemical precursors is an essential requirement due to their feedstock depletion and adverse environmental impacts. In addition, the use of bio-based surfactants can provide unique characteristics and improve the properties and versatility of the colloidal systems in which they are applied, such as emulsions. Here, the emulsification properties of a synthesized biocompatible mannose-based surfactant were investigated. Its behavior was evaluated in the presence of four different natural oils (castor, sunflower, olive and soybean) as well as two different aqueous phases (pure water and phosphate-buffered saline). The results highlighted its interest as surfactant in O/W nanoemulsions for all tested oil and aqueous phases, using a low-energy preparation protocol and relatively low surfactant concentrations. Furthermore, the mannose groups present on the polar head of the surfactant and adsorbed on the surface of the emulsion droplets were shown to retain their native biological properties. The specific mannose-concanavalin A binding was observed in vitro by the designed nanoemulsions, revealing the biorecognition properties of the surfactant and its potential applicability as a nanocarrier.

Specific Binding of Ligand-Functionalized Thermoresponsive Microgels: Effect of Architecture, Ligand Density, and Hydrophobicity

The biomolecular interaction of ligand-presenting switchable microgels is studied with respect to the polymer type, composition, and structure of the microgels. Monodisperse microgels are prepared through precipitation polymerization of N-isopropylacrylamide (PNIPAM microgels) or oligo(ethylene glycol methacrylamide)s (POEGMA microgels) in the presence of crosslinkers or in their absence (self-crosslinked). Functionalization with mannose or biotin as model ligands and affinity measurements upon heating/cooling are conducted to obtain mechanistic insights into how the microgel phase transition affects the specific interactions. In particular, we are interested in adjusting the crosslinking, swelling degree, and ligand density of mannose-functionalized microgels to reversibly catch and release mannose binding Escherichia coli by setting the temperature below or above the microgels' volume phase transition temperature (VPTT). The increased mannose density for collapsed microgels above the VPTT results in stronger E. coli binding. Detachment of E. coli by reswelling the microgels below the VPTT is achieved only for self-crosslinked microgels showing a stronger decrease in ligand density compared to microgels with dedicated crosslinkers. Owing to a reduced mannose density in the shell of POEGMA microgels, their E. coli binding was lower compared to PNIPAM microgels, as supported by ultraresolution microscopy. Importantly, an inverse temperature-controlled binding of microgels decorated with hydrophilic mannose and hydrophobic biotin ligands is observed. This indicates that hydrophobic ligands are inaccessible in the collapsed hydrophobic network above the VPTT, whereas hydrophilic mannose units are then enriched at the microgel-water interface and thus are more accessible.

Dendronized Gelatins Showing Both LCST and UCST-type Thermoresponsive Behavior

Modification of natural polymers with stimuli-responsive synthetic moieties witnesses convergences of superior properties from natural polymers and stimuli-responsiveness to generate new intelligent materials. This was usally performed through synthetic polymers...

Dynamic Glycopeptide Dendrimers: Synthesis and Their Controllable Self-Assembly into Varied Glyco-Nanostructures for the Biomimicry of Glycans

A library of 14 dynamic glycopeptide amphiphilic dendrimers composed of 14 hydrophilic and bioactive saccharides (seven kinds) as dendrons and 7 hydrophobic peptides (di- and tetrapeptides) as arms with β-cyclodextrin (CD) as a core were facially designed and synthesized in several steps. Fourteen saccharides were first conjugated to the C-2 and C-3 positions of CD, forming glycodendrons. Subsequently, seven oligopeptide arms were introduced at the C-6 positions of a CD moiety by an acylhydrazone dynamic covalent bond, resulting in unique Janus amphiphilic glycopeptide dendrimers with precise and varied molecular structures. The kinds of hydrophilic parts of saccharides and hydrophobic parts of peptides were easily varied to prepare a series of amphiphilic Janus glycopeptide dendrimers. Intriguingly, these obtained amphiphilic glycopeptide dendrimers showcased very different self-assembly behaviors from the traditional amphiphilic linear block-copolymers and self-assembled into different glyco-nanostructures with controllable morphologies including glycospheres, worm-like micelles, and fibers depending upon the repeat unit ratio of saccharides and phenylalanine. Both glycodendrons and glycopeptide assemblies displayed strong and specific recognitions with C-type mannose-specific lectin. Moreover, these glycopeptide nanomaterials can encapsulate exemplary hydrophobic molecules such as Nile red (NR). The dye-loaded glycopeptide nanostructures showed a pH-controllable release behavior around the physiological and acidic tumor environment. Furthermore, cell experiments demonstrated that such glyco-nanostructures can further facilitate the functions of a model drug of the pyridone agent to reduce the expression of monocyte chemotactic protein-1 (MCP-1) and interleukin -1beta (IL-1β) in the primary peritoneal macrophages via encapsulating drugs. Considering all the abovementioned advantages including unique and precise structures, bioactivity, targeting, and controllable cargo release, we believe that these findings can not only enrich the library of glycopeptides but also provide a new avenue to the fabrication of smart and structure-controllable glyco-nanomaterials which hold great potential biological applications such as targeted delivery and release of therapeutic and bioactive molecules.

Elastin-like Polypeptide-Based Bioink: A Promising Alternative for 3D Bioprinting

Three-dimensional (3D) bioprinting offers a great alternative to traditional techniques in tissue reconstruction, based on seeding cells manually into a scaffold, to better reproduce organs' complexity. When a suitable bioink is engineered with appropriate physicochemical properties, such a process can advantageously provide a spatial control of the patterning that improves tissue reconstruction. The design of an adequate bioink must fulfill a long list of criteria including biocompatibility, printability, and stability. In this context, we have developed a bioink containing a precisely controlled recombinant biopolymer, namely, elastin-like polypeptide (ELP). This material was further chemoselectively modified with cross-linkable moieties to provide a 3D network through photopolymerization. ELP chains were additionally either functionalized with a peptide sequence Gly-Arg-Gly-Asp-Ser (GRGDS) or combined with collagen I to enable cell adhesion. Our ELP-based bioinks were found to be printable, while providing excellent mechanical properties such as stiffness and elasticity in their cross-linked form. Besides, they were demonstrated to be biocompatible, showing viability and adhesion of dermal normal human fibroblasts (NHF). Expressions of specific extracellular matrix (ECM) protein markers as pro-collagen I, elastin, fibrillin, and fibronectin were revealed within the 3D network containing cells after only 18 days of culture, showing the great potential of ELP-based bioinks for tissue engineering.

Demethylative Alkylation of Methionine Residue by Employing the Sulfonium as the Key Intermediate

Methionine (Met) offers a valuable handle to achieve peptide chemical modification owing to its unique thioether functional group. In contrast with cysteine, the site-selective functionalization of the hydrophobic and redox-sensitive thioether motif on peptides is still challenging, and strategies for diversification on the Met residue are rarely disclosed. Herein we report a transition-metal-free and redox-neutral approach for Met diversification with substrate diversity, which could be applied to synthesize cyclic peptides.

Photooxidation Responsive Elastin-Like Polypeptide Conjugates for Photodynamic Therapy Application

Stimuli-responsive recombinant elastin-like polypeptides (ELPs) are artificial protein polymers derived from the hydrophobic domain of tropoelastin that have attracted significant interest for drug delivery and tissue engineering applications. In the present study, we have conjugated a photosensitizer (PS) to a hydrophobic methionine-containing ELP scaffold, which upon reaction with singlet oxygen (¹O₂) is transformed into a hydrophilic sulfoxide derivative facilitating the disassembly of photosensitizer-delivery particles during the photodynamic therapy (PDT) process. A peripherally substituted carboxy-Zn(II)-phthalocyanine derivative (TT1) bearing a carboxyl group directly linked to the Pc-ring, and presenting an absorption maximum around 680 nm, was selected as PS which simultaneously acted as a photooxidation catalyst. A TT1-ELP[M₁V₃-40] conjugate was prepared from ELP[M₁V₃-40] modified with an alkyne group at the N-terminal chain end, and from TT1-amide-C3-azide by copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. This innovative model photooxidation sensitive PS delivery technology offers promising attributes in terms of temperature-controlled particle formation and oxidation-triggered release, narrow molar mass distribution, reproducibility, scalability, non-immunogenicity, biocompatibility, and biodegradability for pharmaceutical applications in an effort to improve the clinical effectiveness of PDT treatments.

Temperature-Controlled Adhesion to Carbohydrate Functionalized Microgel Films: An E. coli and Lectin Binding Study

The preparation of thermoresponsive mannose functionalized monolayers of poly(N-isopropylacrylamide) microgels and the analysis of the specific binding of concanavalin A (ConA) and E. coli above and below the lower critical solution temperature (LCST) are shown. Via inhibition and direct binding assays it is found that ConA binding is time-dependent, where at short incubation times binding is stronger above the LCST. Given larger incubation times, the interaction of ConA to the microgel network is increased below the LCST when compared to temperatures above the LCST, possibly due to increased ConA diffusion and multivalent binding in the more open microgel network below the LCST. For E. coli, which presents only monovalent lectins and is too large to diffuse into the network, binding is always enhanced above the LCST. This is due to the larger mannose density of the microgel layer above the LCST increasing the interaction to E. coli. Once bound to the microgel layer above the LCST, E. coli cannot be released by cooling down below the LCST. Overall, this suggests that the carbohydrate presenting microgel layers enable specific binding where the temperature-induced transition between swollen and collapsed microgels may increase or decrease binding depending on the receptor size.

Multivalent Elastin-Like Glycopolypeptides: Subtle Chemical Structure Modifications with High Impact on Lectin Binding Affinity

A library of synthetic elastin-like glycopolypeptides were synthesized and screened by microscale thermophoresis to identify key structural parameters affecting lectin binding efficacy. While polypeptide backbone size and glycovalency were found to have little influence, the presence of a linker at the anomeric position of galactose and the absence of positive charge on the polypeptide residue holding the sugar unit were found to be critical for the binding to RCA120.

Lectin and E. coli Binding to Carbohydrate-Functionalized Oligo(ethylene glycol)-Based Microgels: Effect of Elastic Modulus, Crosslinker and Carbohydrate Density

The synthesis of carbohydrate-functionalized biocompatible poly(oligo(ethylene glycol) methacrylate microgels and the analysis of the specific binding to concanavalin A (ConA) and Escherichia coli (E. coli) is shown. By using different crosslinkers, the microgels' size, density and elastic modulus were varied. Given similar mannose (Man) functionalization degrees, the softer microgels show increased ConA uptake, possibly due to increased ConA diffusion in the less dense microgel network. Furthermore, although the microgels did not form clusters with E. coli in solution, surfaces coated with mannose-functionalized microgels are shown to bind the bacteria whereas galactose (Gal) and unfunctionalized microgels show no binding. While ConA binding depends on the overall microgels' density and Man functionalization degree, E. coli binding to microgels' surfaces appears to be largely unresponsive to changes of these parameters, indicating a rather promiscuous surface recognition and sufficiently strong anchoring to few surface-exposed Man units. Overall, these results indicate that carbohydrate-functionalized biocompatible oligo(ethylene glycol)-based microgels are able to immobilize carbohydrate binding pathogens specifically and that the binding of free lectins can be controlled by the network density.

Coupling of RAFT polymerization and chemoselective post-modifications of elastin-like polypeptides for the synthesis of gene delivery hybrid vectors

Hybrid cationic ELPs for nucleic acids transport and delivery were synthetized through the coupling of RAFT polymerization and biorthogonal chemistry of ELPs, introducing a specific number of positive charges to the ELP backbone.

Switchable Adhesion of E. coli to Thermosensitive Carbohydrate-Presenting Microgel Layers: A Single-Cell Force Spectroscopy Study

Adhesion processes at the cellular scale are dominated by carbohydrate interactions, including the attachment and invasion of pathogens. Carbohydrate-presenting responsive polymers can bind pathogens and inhibit pathogen invasion by remote stimuli for the development of new antibiotic strategies. In this work, the adhesion forces of E. coli to monolayers composed of mannose-functionalized microgels with thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and poly(oligo(ethylene glycol)) (PEG) networks are quantified using single-cell force spectroscopy (SCFS). When exceeding the microgels' lower critical solution temperature (LCST), the adhesion increases up to 2.5-fold depending on the polymer backbone and the mannose density. For similar mannose densities, the softer PNIPAM microgels show a significantly stronger adhesion increase when crossing the LCST as compared to the stiffer PEG microgels. This is explained by a stronger shift in swelling, mannose density, and surface roughness of the softer gels when crossing the LCST. When using nonbinding galactose instead of mannose, or when inhibiting bacterial receptors, a certain level of adhesion remains, indicating that also polymer-fimbria entanglements contribute to adhesion. The presented quantitative analysis provides insights into carbohydrate-mediated bacterial adhesion and the relation to material properties and shows the prospects and limitations of interactive polymer materials to control the attachment of bacteria.