Fibril Structure Demonstrates the Role of Iodine Labelling on a Pentapeptide Self‐Assembly

Structure-based improvement of the binding affinity and recognition specificity of peptide competitors to target pediatric IL-5R/IL-5 interaction by gluing halogen bonds at their complex interface

Human interleukin-5 (IL-5) cytokine mediates the development of eosinophils and is involved in a variety of immune inflammatory responses that play a major role in the pathogenesis of childhood asthma, leukemia, and other pediatric allergic diseases. The immunomodulatory cytokine functions by binding to its cognate cell surface receptor IL-5R in a sheet-by-sheet manner, which can be conformationally mimicked and competitively disrupted by a double-stranded cyclic AF18748 peptide. In this study, we systematically examined the co-crystallized complex structure of human IL-5R with AF18748 peptide and rationally designed a halogen bond to glue at the protein-peptide complex interface by substituting the indole moiety of AF18748 Trp13 residue with a halogen atom (X = F, Cl, Br, or I). High-level theoretical calculations imparted presence of the halogen bond between the oxygen atom (O) of IL-5R Glu58 backbone and the halogen atom (X) of AF18748 Trp13 side chain. Experimental assays confirmed that the halogen bond can promote peptide binding moderately or considerably. More importantly, the halogen bond not only enhances peptide affinity to IL-5R, but also improves peptide selectivity for its cognate IL-5R over other noncognate IL-R proteins. As might be expected, the affinity and selectivity conferred by halogen bond increase consistently in the order: H < F < Cl < Br < I. Structural modeling revealed that the halogen bond plus its vicinal π-cation-π stacking co-define a ringed noncovalent system at the complex interface, which involves a synergistic effect to effectively improve the peptide binding potency and recognition specificity.

Creating an Amyloid 'Kaleidoscope' Using Short Iodinated Peptides

Amyloid fibrils formed by peptides with different sequences exhibit diversified morphologies, material properties and activities, making them valuable for developing functional bionanomaterials. However, the molecular understanding underlying the structural diversity of peptide fibrillar assembly at atomic level is still lacking. In this study, by using cryogenic electron microscopy, we first revealed the structural basis underlying the highly reversible assembly of 1 GFGGNDNFG9 (referred to as hnRAC1) peptide fibril. Furthermore, by installing iodine at different sites of hnRAC1, we generated a collection of peptide fibrils with distinct thermostability. By determining the atomic structures of the iodinated fibrils, we discovered that iodination at different sites of the peptide facilitates the formation of diverse halogen bonds and triggers the assembly of entirely different structures of iodinated fibrils. Finally, based on this structural knowledge, we designed an iodinated peptide that assembles into new atomic structures of fibrils, exhibiting superior thermostability, that aligned with our design. Our work provides an in-depth understanding of the atomic-level processes underlying the formation of diverse peptide fibril structures, and paves the way for creating an amyloid "kaleidoscope" by employing various modifications and peptide sequences to fine-tune the atomic structure and properties of fibrillar nanostructures.

Acid⋅⋅⋅Amide Supramolecular Synthon for Tuning Amino Acid-Based Hydrogels' Properties

Supramolecular hydrogels formed by the self-assembly of N-Fmoc-l-phenylalanine derivatives are gaining relevance for several applications in the materials and biomedical fields. In the challenging attempt to predict or tune their properties, we selected Fmoc-pentafluorophenylalanine (1) as a model efficient gelator, and studied its self-assembly in the presence of benzamide (2), a non-gelator able to form strong hydrogen bonds with the amino acid carboxylic group. Equimolar mixtures of 1 and 2 in organic solvents afforded a 1 : 1 co-crystal thanks to the formation of an acid⋅⋅⋅amide heterodimeric supramolecular synthon. The same synthon occurred in the transparent gels formed by mixing the two components in 1 : 1 ratio in aqueous media, as revealed by structural, spectroscopic, and thermal characterizations performed on both the co-crystal powder and the lyophilized hydrogel. These findings revealed the possibility of modulating the properties of amino acid-based hydrogels by involving the gelator in the formation of a co-crystal. Such a crystal engineering-based approach is shown also to be useful for the time-delayed release of suitable bioactive molecules, when involved as hydrogel coformers.

Computation meets experiment: identification of highly efficient fibrillating peptides

Self-assembling peptides are of huge interest for biological, medical and nanotechnological applications. The enormous chemical variety that is available from the 20 amino acids offers potentially unlimited peptide sequences, but it is currently an issue to predict their supramolecular behavior in a reliable and cheap way. Herein we report a computational method to screen and forecast the aqueous self-assembly propensity of amyloidogenic pentapeptides. This method was found also as an interesting tool to predict peptide crystallinity, which may be of interest for the development of peptide based drugs.

The Antioxidant Properties of Selected Varieties of Pumpkin Fortified with Iodine in the Form of Potassium Iodide and Potassium Iodate

This study aimed to investigate the use of selected pumpkin varieties as carriers of potassium iodide (KI) and potassium iodate (KIO₃) at different concentrations (2.3, 0.23, and 0.023 mg/100 g). It was hypothesized that the concentrations and form of iodine fortification in pumpkins affect the antioxidant activity of pumpkins. The results showed a high recovery of the introduced iodine in all pumpkin varieties after drying, as well as high iodine stability during storage, especially for KIO₃. However, statistical analysis confirmed a relationship between the forms and concentration of iodine and the ABTS cation radical and the DPPH radical test results. In the systems with iodine concentration at 0.023 and 0.23 mg/100 g, the antioxidant activity did not change. However, for all pumpkin varieties fortified with a KIO₃ concentration at 3.9 mg/100 g (2.3 mg/100 g of iodine), a statistically significant decrease in free-radical scavenging was confirmed. Therefore, for maximum effectiveness in pumpkin's free-radical scavenging indices, it is suggested to introduce iodine in the form of KI and KIO₃, but in controlled concentrations. However, KIO₃ should be added at a maximum amount of 0.39 mg/100 g.

Synthesis of Amino Acids Bearing Halodifluoromethyl Moieties and Their Application to p53-Derived Peptides Binding to Mdm2/Mdm4

Introduction

Therapeutic peptides are a significant class of drugs in the treatment of a wide range of diseases. To enhance their properties, such as stability or binding affinity, they are usually chemically modified. This includes, among other techniques, cyclization of the peptide chain by bridging, modifications to the backbone, and incorporation of unnatural amino acids. One approach previously established, is the use of halogenated aromatic amino acids. In principle, they are thereby enabled to form halogen bonds (XB). In this study, we focus on the -R-CF₂X moiety (R = O, NHCO; X = Cl, Br) as an uncommon halogen bond donor. These groups enable more spatial variability in protein-protein interactions. The chosen approach via Fmoc-protected building blocks allows for the incorporation of these modified amino acids in peptides using solid-phase peptide synthesis.

Results and Discussion

Using a competitive fluorescence polarization assay to monitor binding to Mdm4, we demonstrate that a p53-derived peptide with Lys24Nle(εNHCOCF₂X) exhibits an improved inhibition constant K_i compared to the unmodified peptide. Decreasing K_i values observed with the increasing XB capacity of the halogen atoms (F ≪ Cl < Br) indicates the formation of a halogen bond. By reducing the side chain length of Nle(εNHCOCF₂X) to Abu(γNHCOCF₂X) as control experiments and through quantum mechanical calculations, we suggest that the observed affinity enhancement is related to halogen bond-induced intramolecular stabilization of the α-helical binding mode of the peptide or a direct interaction with His54 in human Mdm4.

Hydrogen- and halogen bond synergy in the self-assembly of 3,5-dihalo-tyrosines: structural and theoretical insights

Halogenation, generally introduced on aromatic aminoacids, is becoming a key supramolecular tool in peptides. Herein, we report the crystal structures and DFT study of two bis-halogenated tyrosines showing the subtle...