Design, Synthesis, and Evaluation of N- and C-Terminal Protein Bioconjugates as G Protein-Coupled Receptor Agonists

A G protein-coupled receptor (GPCR) agonist protein, thaumatin, was site-specifically conjugated at the N- or C-terminus with a fluorophore for visualization of GPCR:agonist interactions. The N-terminus was specifically conjugated using a synthetic 2-pyridinecarboxyaldehyde reagent. The interaction profiles observed for N- and C-terminal conjugates were varied; N-terminal conjugates interacted very weakly with the GPCR of interest, whereas C-terminal conjugates bound to the receptor. These chemical biology tools allow interactions of therapeutic proteins:GPCR to be monitored and visualized. The methodology used for site-specific bioconjugation represents an advance in application of 2-pyridinecarboxyaldehydes for N-terminal specific bioconjugations.

The death of the Job plot, transparency, open science and online tools, uncertainty estimation methods and other developments in supramolecular chemistry data analysis

Data analysis is central to understanding phenomena in host-guest chemistry. We describe here recent developments in this field starting with the revelation that the popular Job plot method is inappropriate for most problems in host-guest chemistry and that the focus should instead be on systematically fitting data and testing all reasonable binding models. We then discuss approaches for estimating uncertainties in binding studies using case studies and simulations to highlight key issues. Related to this is the need for ready access to data and transparency in the methodology or software used, and we demonstrate an example a webportal () that aims to address this issue. We conclude with a list of best-practice protocols for data analysis in supramolecular chemistry that could easily be translated to other related problems in chemistry including measuring rate constants or drug IC₅₀ values.

Glyoxylamide-based self-assembly hydrogels for sustained ciprofloxacin delivery

Glyoxylamide-based hydrogels have high ciprofloxacin (CIP) loading capacity and demonstrate a sustained release profile of over 15 days.

Formation of non-spherical polymersomes driven by hydrophobic directional aromatic perylene interactions

Polymersomes, made up of amphiphilic block copolymers, are emerging as a powerful tool in drug delivery and synthetic biology due to their high stability, chemical versatility, and surface modifiability. The full potential of polymersomes, however, has been hindered by a lack of versatile methods for shape control. Here we show that a range of non-spherical polymersome morphologies with anisotropic membranes can be obtained by exploiting hydrophobic directional aromatic interactions between perylene polymer units within the membrane structure. By controlling the extent of solvation/desolvation of the aromatic side chains through changes in solvent quality, we demonstrate facile access to polymersomes that are either ellipsoidal or tubular-shaped. Our results indicate that perylene aromatic interactions have a great potential in the design of non-spherical polymersomes and other structurally complex self-assembled polymer structures.

Protease sensing using nontoxic silicon quantum dots

Herein is presented a proof-of-concept study of protease sensing that combines nontoxic silicon quantum dots (SiQDs) with Förster resonance energy transfer (FRET). The SiQDs serve as the donor and an organic dye as the acceptor. The dye is covalently attached to the SiQDs using a peptide linker. Enzymatic cleavage of the peptide leads to changes in FRET efficiency. The combination of interfacial design and optical imaging presented in this work opens opportunities for use of nontoxic SiQDs relevant to intracellular sensing and imaging.

Controlling self-assembly of diphenylalanine peptides at high pH using heterocyclic capping groups

Using small angle neutron scattering (SANS), it is shown that the existence of pre-assembled structures at high pH for a capped diphenylalanine hydrogel is controlled by the selection of N-terminal heterocyclic capping group, namely indole or carbazole. At high pH, changing from a somewhat hydrophilic indole capping group to a more hydrophobic carbazole capping group results in a shift from a high proportion of monomers to self-assembled fibers or wormlike micelles. The presence of these different self-assembled structures at high pH is confirmed through NMR and circular dichroism spectroscopy, scanning probe microscopy and cryogenic transmission electron microscopy.

A Peptide Amphiphile Organogelator of Polar Organic Solvents

A peptide amphiphile is reported, that gelates a range of polar organic solvents including acetonitrile/water, N,N-dimethylformamide and acetone, in a process dictated by β-sheet interactions and facilitated by the presence of an alkyl chain. Similarities with previously reported peptide amphiphile hydrogelators indicate analogous underlying mechanisms of gelation and structure-property relationships, suggesting that peptide amphiphile organogel design may be predictably based on hydrogel precedents.

The Use of Hydrogels as Biomimetic Materials for 3D Cell Cultures

With the recent developments in cell cultures and biomimetic materials, there is growing evidence indicating that long-established two-dimensional (2D) cell culture techniques are slowly being phased out and replaced with three-dimensional (3D) cell cultures. This is due to the 3D cell cultures better mimicking the natural extracellular matrix (ECM) where cells are found. The emergence of self-assembled hydrogels as an ECM mimic has revolutionised the field owing to their ability to closely simulate the fibrous nature of the ECM. Here, we review recent progress in using hydrogels as biomimetic materials in 3D cell cultures, particularly supramolecular peptide hydrogels. With greater comprehension of the behaviour of cells in these hydrogels, a cell culture system that can be used in a wide array of 3D culture-based applications can be developed.

Tuning hydrogels through metal-based gelation triggers

N-terminal capped tripeptides self-assemble into hydrogels with tuneable properties depending on gelation trigger, giving differences in structure, stiffness and biocompatibility.

Design, synthesis, and characterisation of glyoxylamide-based short peptides as self-assembled gels

First example of glyoxylamide-based short peptides which can encapsulate organic solvents and water at relatively low concentrations.

Cyclic peptide unguisin A is an anion receptor with high affinity for phosphate and pyrophosphate

Unguisin A (1) is a marine-derived, GABA-containing cyclic heptapeptide with a high binding affinity for phosphates.

Assessing cooperativity in supramolecular systems

In this tutorial review, different aspects of cooperativity in supramolecular chemistry and their thermodynamic analysis are discussed.

Polymersomes with Asymmetric Membranes Based on Readily Accessible Di- and Triblock Copolymers Synthesized via SET-LRP

One of the hallmarks of nature is compartmentalization, and natural cell membranes are often asymmetric in terms of the inner and outer side. This communication describes work toward synthesizing such an asymmetric membrane from the bottom-up. A family of amphiphilic di- and triblock copolymers were synthesized via Cu(0)-mediated single electron transfer-living radical polymerization with the aim to generate polymer vesicles, or polymersomes, with an asymmetric membrane. Self-assembly of these polymeric amphiphiles in aqueous media was investigated using asymmetric field-flow fractionation and cryo-electron microscopy. Utilizing mixtures of diblock copolymers with differing hydrophilic moieties resulted in the formation of vesicles with an asymmetric segregation of charge between the inner and outer leaflet, confirmed by zeta potential measurements. These polymers, synthesized in good yields and using a biologically compatible method to induce self-assembly, have a promising range of applications from nanomedicine to synthetic cell research.

Effect of heterocyclic capping groups on the self-assembly of a dipeptide hydrogel

The mechanism and design rules associated with the self-assembly of short peptides into hydrogels is currently not well understood. In this work, four diphenylalanine-based peptides have been synthesised, bearing heterocyclic capping groups which have different degrees of hydrogen bonding potential and nitrogen substitution. For these four peptides, zeta potential and electrical impedance spectroscopy measurements were undertaken to monitor gelation, with the impedance data showing different gelation times for each peptide hydrogel. Through a combination of atomic force microscopy and rheological measurmeents, including dynamic strain and frequency sweeps, and thixotropic tests, the relationship between the mechanism of self-assembly in these hydrogels and their macroscopic behaviour can be established. It is observed that the degree of nitrogen substitution affects the self-assembly mechanisms of the hydrogels and as such, that there is an interplay between branching and bundling self-assembly pathways that are responsible for the final properties of each hydrogel.

A Capped Dipeptide Which Simultaneously Exhibits Gelation and Crystallization Behavior

Short peptides capped at their N-terminus are often highly efficient gelators, yet notoriously difficult to crystallize. This is due to strong unidirectional interactions within fibers, resulting in structure propagation only along one direction. Here, we synthesize the N-capped dipeptide, benzimidazole-diphenylalanine, which forms both hydrogels and single crystals. Even more remarkably, we show using atomic force microscopy the coexistence of these two distinct phases. We then use powder X-ray diffraction to investigate whether the single crystal structure can be extrapolated to the molecular arrangement within the hydrogel. The results suggest parallel β-sheet arrangement as the dominant structural motif, challenging existing models for gelation of short peptides, and providing new directions for the future rational design of short peptide gelators.