Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Increasing Elasticity through Changes in the Secondary Structure of Gelatin by Gelation in a Microsized Lipid Space

Even though microgels are used in a wide variety of applications, determining their mechanical properties has been elusive because of the difficulties in analysis. In this study, we investigated the surface elasticity of a spherical microgel of gelatin prepared inside a lipid droplet by using micropipet aspiration. We found that gelation inside a microdroplet covered with lipid membranes increased Young's modulus E toward a plateau value E* along with a decrease in gel size. In the case of 5.0 wt % gelatin gelled inside a microsized lipid space, the E* for small microgels with R ≤ 50 μm was 10-fold higher (35-39 kPa) than that for the bulk gel (∼3 kPa). Structural analysis using circular dichroism spectroscopy and a fluorescence indicator for ordered beta sheets demonstrated that the smaller microgels contained more beta sheets in the structure than the bulk gel. Our finding indicates that the confinement size of gelling polymers becomes a factor in the variation of elasticity of protein-based microgels via secondary structure changes.

Balancing hydrophobicity and sequence pattern to influence self-assembly of amphipathic peptides

Amphipathic peptides with alternating polar and nonpolar amino acid sequences efficiently self-assemble into functional β-sheet fibrils as long as the nonpolar residues have sufficient hydrophobicity. For example, the Ac-(FKFE)2 -NH2 peptide rapidly self-assembles into β-sheet bilayer nanoribbons, while Ac-(AKAE)2 -NH2 fails to self-assemble under similar conditions due to the significantly reduced hydrophobicity and β-sheet propensity of Ala relative to Phe. Herein, we systematically explore the effect of substituting only two of the four Ala residues at various positions in the Ac-(AKAE)2 -NH2 peptide with amino acids of increasing hydrophobicity, β-sheet potential, and surface area (including Phe, 1-naphthylalanine (1-Nal), 2-naphthylalanine (2-Nal), cyclohexylalanine (Cha), and pentafluorophenylalanine (F5 -Phe)) on the self-assembly propensity of the resulting sequences. It was found that double Phe variants, regardless of the position of substitution, failed to self-assemble under the conditions used in this study. In contrast, all double 1-Nal and 2-Nal variants readily self-assembled, albeit at differing rates depending on the substitution patterns. To determine whether this was due to hydrophobicity or side chain surface area, we also prepared double Cha and F5 -Phe variant peptides (both side chain groups are more hydrophobic than Phe). Each of these variants also underwent effective self-assembly, with the aromatic F5 -Phe peptides doing so with greater efficiency. These findings provide insight into the role of amino acid hydrophobicity and sequence pattern on self-assembly proclivity of amphipathic peptides and on how targeted substitutions of nonpolar residues in these sequences can be exploited to tune the characteristics of the resulting self-assembled materials.

The Physiological and Pathological Implications of the Formation of Hydrogels, with a Specific Focus on Amyloid Polypeptides

Hydrogels are water-swollen and viscoelastic three-dimensional cross-linked polymeric network originating from monomer polymerisation. Hydrogel-forming polypeptides are widely found in nature and, at a cellular and organismal level, they provide a wide range of functions for the organism making them. Amyloid structures, arising from polypeptide aggregation, can be damaging or beneficial to different types of organisms. Although the best-known amyloids are those associated with human pathologies, this underlying structure is commonly used by higher eukaryotes to maintain normal cellular activities, and also by microbial communities to promote their survival and growth. Amyloidogenesis occurs by nucleation-dependent polymerisation, which includes several species (monomers, nuclei, oligomers, and fibrils). Oligomers of pathological amyloids are considered the toxic species through cellular membrane perturbation, with the fibrils thought to represent a protective sink for toxic species. However, both functional and disease-associated amyloids use fibril cross-linking to form hydrogels. The properties of amyloid hydrogels can be exploited by organisms to fulfil specific physiological functions. Non-physiological hydrogelation by pathological amyloids may provide additional toxic mechanism(s), outside of membrane toxicity by oligomers, such as physical changes to the intracellular and extracellular environments, with wide-spread consequences for many structural and dynamic processes, and overall effects on cell survival.

Water-Soluble Sericin Protein Enabling Stable Solid-Electrolyte Interphase for Fast Charging High Voltage Battery Electrode

Spinel LiNi_0.5 Mn_1.5 O₄ (LNMO) is the most promising cathode material for achieving high energy density lithium-ion batteries attributed to its high operating voltage (≈4.75 V). However, at such high voltage, the commonly used battery electrolyte is suffered from severe oxidation, forming unstable solid-electrolyte interphase (SEI) layers. This would induce capacity fading, self-discharge, as well as inferior rate capabilities for the electrode during cycling. This work first time discovers that the electrolyte oxidation is effectively negated by introducing an electrochemically stable silk sericin protein, which is capable to stabilize the SEI layer and suppress the self-discharge behavior for LNMO. In addition, robust mechanical support of sericin coating maintains the structural integrity during the fast charging/discharging process. Benefited from these merits, the sericin-based LNMO electrode possesses a much lower Li-ion diffusion energy barrier (26.1 kJ mol^-1 ) for than that of polyvinylidene fluoride-based LNMO electrode (37.5 kJ mol^-1 ), delivering a remarkable high-rate performance. This work heralds a new paradigm for manipulating interfacial chemistry of electrode to solve the key obstacle for LNMO commercialization, opening a powerful avenue for unlocking the current challenges for a wide family of high operating voltage cathode materials (>4.5 V) toward practical applications.

Application of NMR to studies of intrinsically disordered proteins

The prevalence of intrinsically disordered protein regions, particularly in eukaryotic proteins, and their clear functional advantages for signaling and gene regulation have created an imperative for high-resolution structural and mechanistic studies. NMR spectroscopy has played a central role in enhancing not only our understanding of the intrinsically disordered native state, but also how that state contributes to biological function. While pathological functions associated with protein aggregation are well established, it has recently become clear that disordered regions also mediate functionally advantageous assembly into high-order structures that promote the formation of membrane-less sub-cellular compartments and even hydrogels. Across the range of functional assembly states accessed by disordered regions, post-translational modifications and regulatory macromolecular interactions, which can also be investigated by NMR spectroscopy, feature prominently. Here we will explore the many ways in which NMR has advanced our understanding of the physical-chemical phase space occupied by disordered protein regions and provide prospectus for the future role of NMR in this emerging and exciting field.

Multifunctional thermoresponsive designer peptide hydrogels

We report the synthesis and characterization of multifunctional peptides comprised of a hydrogel forming β-sheet peptide segment and a matrix metalloproteinase 2 substrate containing a propargylglycinyl linker that is further derivatized with an RGD peptide sequence via "click" chemistry. In contrast to currently known systems, these multifunctional peptides formed gels that are stiffer than those formed by their respective precursors. All the peptides showed reversible thermoresponsive properties, which render them as suitable lead systems for a variety of possible biomedical applications.

STATEMENT OF SIGNIFICANCE

In general, it has been frequently observed that chemical biofunctionalization of peptide hydrogels adversely affects peptide assembly, hydrogel formation or mechanical properties, which severely compromises their application. A functionalization protocol that allows to generate peptide hydrogels that display significantly improved mechanical properties over their unfunctionalized counterparts is reported in this work. These peptides also showed thermoresponsive viscoelastic characteristics, including an example of a peptide hydrogel that displays lower critical solution temperature behaviour.

Understanding the metal mediated assembly and hydrogel formation of a β-hairpin peptide

We report the Zn²⁺-mediated hydrogel formation of a β-hairpin peptide that proceeded via an intermolecular metal- coordination mechanism.