The effect of pH and calcium ions on the stability of amphiphilic and anionic β‐sheet peptide hydrogels

Abstract

Amphiphilic peptides can form bottom-up-designed self-assembled hydrogels composed of elongated fibril matrices that could find uses in various biologically-related systems, acting as platforms for drug delivery or scaffolds that mimic extracellular matrices in tissue regeneration systems. We have previously reported that the amphiphilic and anionic β-sheet forming peptide, Pro-Asp-(Phe-Asp)5 -Pro, P(FD)-5, generates hydrogels that template calcium-phosphate mineral and as such, were able to enhance bone formation in vivo. Our earlier results prompted us to further exploit the effects of pH and calcium ion concentration on P(FD)-5 peptide in solution, in hydrogels and in mineral-loaded hydrogel compositions. Circular dichroism-based characterization of solutions of the peptide demonstrated transitions between the unfolded state to a β-sheet structure as function of peptide concentration, pH and calcium ion concentration. FTIR measurements were employed to monitor differences between the structure of the peptide in solution and in hydrogels. Rheology and dissolution studies demonstrated the improved stability of hydrogels prepared by a two-step procedure, where the peptides are dissolved and self-assemble in the first step, while in the second step, calcium ions are allowed to adsorb onto the system. These results, highlighting the effects of a few central factors on the structure, assembly and stability of amphiphilic and anionic β-sheet peptide systems, will contribute to the further development of designed self-assembled peptide systems from solutions to hydrogels and hydrogel-loaded matrices, such as mineral putty compositions.

Stacking interactions by two Phe side chains stabilize and orient assemblies of even the minimal amphiphilic β-sheet motif

“…Phe-Glu-Phe 5 mM solutions were further characterized by CD (circular dichroism) measurements at a range of pH values below and above this apparent pK a . As stacking interactions were not observed in previously reported CD measurements of 13 residue peptides that exhibit this dyad motif, 29 we were interested in determining whether the five residue version of this motif, i.e. 1b) reported previously for Phe amino acid, 25 the dipeptide Phe-Phe 18 and poly-Phe.…”

Changes of Thermostability, Organic Solvent, and pH Stability in Geobacillus zalihae HT1 and Its Mutant by Calcium Ion

“…The conformational changes of secondary structure elements in the presence of calcium ions has been reported in other proteins such as recombinant human bone morphogenetic protein 2 (rhBMP-2) with the increase of β-sheet and turn percentage as compared with proteins in the absence of calcium ion [54]. The formation of β-sheet structure in amphiphilic peptide increased sharply with respect to the unfolded structure with the addition of calcium ion [55].…”

Supramolecular Peptide Nanofiber Hydrogels for Bone Tissue Engineering: From Multihierarchical Fabrications to Comprehensive Applications

“…[ 53 ] When hydrogels are obtained by adjusting pH or the ionic strength, oppositely charged ions are needed to screen the resistance among peptides and exert as cross‐linkers. Compared with positive self‐repulsive peptides, negative modules, such as (LE)8 (CH 3 COLELELELELELELELENH 2 ) [ 53 ] and PFD‐5 (PDFDFDFDFDP), [ 54 ] may be promising for bone tissue engineering because abundant carboxyl group could efficaciously induce biomineralization. Meanwhile, when hydrogels are formed by coassembly of two complementary self‐repulsive peptides, the initial pH and ionic strength may be preserved without microenvironment change; thus, seed cells or bioactive factors could be directly loaded to peptide storage solutions under physiological conditions, making coassembling self‐repulsive SPNHs more biocompatible than stimuli‐triggered SPNHs.…”