Enzymatically triggered self-assembly of poly(ethylene glycol)-attached oligopeptides into well-organized nanofibers

Self-assembly of tamarind seed polysaccharide via enzymatic depolymerization and degalactosylation enhanced ice recrystallization inhibition activity

Polysaccharides are becoming potential candidates for developing food-grade cryoprotectants due to their extensive accessibility and health-promoting effects. However, unremarkable ice recrystallization inhibition (IRI) activity and high viscosity limit their practical applications in some systems. Our previous study found a galactoxyloglucan polysaccharide from tamarind seed (TSP) showing moderate IRI activity. Herein, the enhancement of the IRI performance of TSP via enzymatic depolymerization and degalactosylation-induced self-assembly was reported. TSP was depolymerized and subsequently removed ∼40 % Gal, which induced the formation of supramolecular rod-like fiber self-assembles and exhibited a severalfold enhancement of IRI. Ice shaping assay did not show obvious faceting of ice crystals, indicating that both depolymerized and self-assembled TSP showed very weak binding to ice. Molecular dynamics simulation confirmed the absence of molecular complementarity with ice. Further, it highlighted that degalactosylation did not cause significant changes in local hydration properties of TSP from the view of a single oligomer. The inconsistency between molecular simulation and macroscopic IRI effect proposed that the formation of unique supramolecular self-assemblies may be a key requirement for enhancing IRI activity. The findings of this study provided a new opportunity to enhance the applied potential of natural polysaccharides in food cryoprotection.

Enzyme-Triggered Antifouling Coatings: Switching Bioconjugate Adsorption via Proteolytically Cleavable Interfering Domains

Protease activable antifouling coatings based on peptide-poly(ethylene glycol) conjugates are shown. The material-specific adsorption of a bioconjugate is temporarily suppressed by extending a titanium binding sequence with a proteolytically cleavable epitope and a suitable interfering domain. The adsorption of the PEG-peptide conjugates onto titanium substrates can be regained by cleaving the interfering domain with Tobacco Etch Virus protease. This activates peptide-mediated PEGylation of titanium surfaces and results in coatings that are stable against dilution and suppress nonreversible adsorption of blood protein models. Effects of branched and linear peptidic binding domains on coating stability and antifouling properties are elucidated.

PEG-peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG-peptides is reviewed, including self-assemblies formed by PEG-peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized.

Enzyme responsive materials: design strategies and future developments

Enzyme responsive materials (ERMs) are a class of stimuli responsive materials with broad application potential in biological settings. This review highlights current and potential future design strategies for ERMs and provides an overview of the present state of the art in the area.

Switching of Self-Assembly in a Peptide Nanostructure with a Specific Enzyme

Peptide self-assembly has been shown to be a useful tool for the preparation of bioactive nanostructures, and recent work has demonstrated their potential as therapies for regenerative medicine. In principle, one route to make these nanostructures more biomimetic would be to incorporate in their molecular design the capacity for biological sensing. We report here on the use of a reversible enzymatic trigger to control the assembly and disassembly of peptide amphiphile (PA) nanostructures. The PA used in these studies contained a consensus substrate sequence specific to protein kinase A (PKA), a biological enzyme important for intracellular signaling that has also been shown to be an extracellular cancer biomarker. Upon treatment with PKA, this PA molecule becomes phosphorylated causing the high aspect-ratio filamentous PA nanostructures to disassemble. Treatment with an enzyme to cleave the phosphate group results in reformation of the filamentous nanostructures. We also show that disassembly in the presence of PKA allows the enzyme-triggered release of an encapsulated cancer drug. In addition, these drug-loaded nanostructures were found to induce preferential cytotoxicity in a cancer cell line that is known to secrete high levels of PKA. This ability to control nanostructure through an enzymatic switch could allow for the preparation of highly sophisticated and biomimetic materials that incorporate a biological sensing capability to enable therapeutic specificity.

Peptide synthesis and self-assembly

Peptides and proteins are the most diverse building blocks in biomolecular self-assembly in terms of chemistry, nanostructure formation and functionality. Self-assembly is an intrinsic property of peptides. In this chapter, we attempt to address the following issues: How can we synthesize a self-assembling peptide? What are the fundamental physical and chemical principles that underpin peptide self-assembly? How can we learn to finely control peptide self-assembly? The merits of answering these questions are inspiring both for biology and medicine in terms of new opportunities for understanding, preventing and curing of diseases, and for nanotechnology in terms of new prescribed routes to achieving peptide-based nanostructures with a range of properties appropriate for specific applications.

PEGylated amyloid peptide nanocontainer delivery and release system

A micellar nanocontainer delivery and release system is designed on the basis of a peptide-polymer conjugate. The hybrid molecules self-assemble into micelles comprising a modified amyloid peptide core surrounded by a PEG corona. The modified amyloid peptide previously studied in our group forms helical ribbons based on a beta-sheet motif and contains beta-amino acids that are excluded from the beta-sheet structure, thus being potentially useful as fibrillization inhibitors. In the model peptide-PEG hybrid system studied, enzymatic degradation using alpha-chymotrypsin leads to selective cleavage close to the PEG-peptide linkage, break up of the micelles, and release of peptides in unassociated form. The release of monomeric peptide is useful because aggregation of the released peptide into beta-sheet amyloid fibrils is not observed. This concept has considerable potential in the targeted delivery of peptides for therapeutic applications.

Exploiting biocatalysis in peptide self-assembly

This review article covers recent developments in the use of enzyme-catalyzed reactions to control molecular self-assembly (SA), an area that merges the advantages of biocatalysis with soft materials self-assembly. This approach is attractive because it combines biological (chemo-, regio-, and enantio-) selectivity with the versatility of bottom up nanofabrication through dynamic SA. We define enzyme-assisted SA (e-SA) as the production of molecular building blocks from nonassembling precursors via enzymatic catalysis, where molecular building blocks form ordered structures via noncovalent interactions. The molecular design of SA precursors is discussed in terms of three key components related to (i) enzyme recognition, (ii) molecular switching mechanisms, and (iii) supramolecular interactions that underpin SA. This is followed by a discussion of a number of unique features of these systems, including spatiotemporal control of nucleation and structure growth, the possibility of controlling mechanical properties and the defect correcting and component selecting capabilities of systems that operate under thermodynamic control. Applications in biomedicine (biosensing, controlled release, matrices for wound healing, controlling cell fate by gelation) and bio(nano)technology (biocatalysts immobilization, nanofabrication, templating, and intracellular imaging) are discussed. Overall, e-SA allows for unprecedented control over SA processes and provides a step forward toward production of nanostructures of higher complexity and with fewer defects as desired for next generation nanomaterials.

Polymer-peptide block copolymers - an overview and assessment of synthesis methods

Incorporating peptide blocks into block copolymers opens up new realms of bioactive or smart materials. Because there are such a variety of peptides, polymers, and hybrid architectures that can be imagined, there are many different routes available for the synthesis of these chimera molecules. This review summarizes the contemporary strategies in combining synthesis techniques to create well-defined peptide-polymer hybrids that retain the vital aspects of each disparate block. Living polymerization can be united with the molecular-level control afforded by peptide blocks to yield block copolymers that not only have precisely defined primary structures, but that also interact with other (bio)molecules in a well defined manner.

Nanofiber applications for burn care

Nanotechnology is a growing field of manufactured materials with sizes less than 1 mum, and it is particularly useful in the field of medicine because these applications replicate components of a cell's in vivo environment. Nanofibers, which mimic collagen fibrils in the extracellular matrix (ECM), can be created from a host of natural and synthetic compounds and have multiple properties that may be beneficial to burn wound care. These properties include a large surface-area-to-volume ratio, high porosity, improved cell adherence, proliferation and migration, and controlled in vivo degradation rates. The large surface area of nanofiber mats allows for increased interaction with compounds and provides a mechanism for sustained release of antibiotics, analgesics, or growth factors into burn wounds; high porosity allows diffusion of nutrients and waste. Improved cell function on these scaffolds will promote healing. Controlled degradation rates of these scaffolds will promote scaffold absorption after its function is no longer required. The objective of this article is to review the current literature describing nanofibers and their potential application to burn care.

Disassembling peptide-based fibres by switching the hydrophobic-hydrophilic balance

Amyloid-like model peptides, modified on the N-terminus with an alkyl tail and on the C-terminus with a PEG chain, yielded fibres that were susceptible to triggered disassembly by removal of the alkyl chain, which affected the hydrophobic-hydrophilic balance.