pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

Abstract

Peptide-based biopolymers represent highly promising biocompatible materials with multiple applications, such as tailored drug delivery, tissue engineering and regeneration, and as stimuli-responsive materials. Herein, we report the pH- and concentration-dependent self-assembly and conformational transformation of the newly synthesized octapeptide PEP-1. At pH 7.4, PEP-1 forms β-sheet-rich secondary structures into fractal-like morphologies, as verified by circular dichroism (CD), Fourier-transform infrared (FTIR) spectroscopy, thioflavin T (ThT) fluorescence spectroscopy assay, and atomic force microscopy (AFM). Upon changing the pH value (using pH 5.5 and 13.0), PEP-1 forms different types of secondary structures and resulting morphologies due to electrostatic repulsion between charged amino acids. PEP-1 can also form helical or random-coil secondary structures at a relatively low concentration. The obtained pH-sensitive self-assembly behavior of the target octapeptide is expected to contribute to the development of novel drug nanocarrier assemblies.

Control over Multiple Nano‐ and Secondary Structures in Peptide Self‐Assembly

“…AFM reveals small elliptical or nanorod‐like structures (Figure 1 f) that are in good agreement with the destabilization of the PEP‐1 assembly at pH 5.5 (Figure 1 a). These results can be explained by the decreased solubility of PEP‐1 at pH 5.5 due to electrostatic repulsions among positively charged ammonium ions (from Lys + ), which hamper not only the molecular orientations during self‐assembly, but also long‐range supramolecular polymerization [6c,d, 14] …”

“…At high concentrations, the possibility of peptide molecules to come into closer contact and engage in strong intermolecular H‐bonding is more likely, thus facilitating the β‐sheet rich secondary structures. Dilution decreases the population of molecules and, consequently, their ability to form organized H‐bonds ultimately leading to irregular spherical nanoparticles of different sizes [6d] . We attempted to unravel whether interconversion between both states (twisted β‐sheet and random coil) is possible at room temperature and at a given concentration over time.…”

“…[13] This secondary structure is further supported by FT‐IR studies: two intense peaks at 1632 and 1674 cm −1 are observed in the amide‐I region, indicating intermolecular antiparallel β‐sheet arrangement (Figure 1 b ). [ 6c , 6d ] Additional proof of the existence of β‐sheet structures is provided by Thioflavin T (ThT) fluorescence assay, where the emission intensity of the mixture PEP‐1 /ThT is considerably higher than that of the free ThT (Figure S7). [ 6c , 6d ] To gain insights into the aggregate morphology formed by PEP‐1 at neutral pH, atomic force microscopy (AFM) studies on mica were conducted.…”

“…[ 6c , 6d ] Additional proof of the existence of β‐sheet structures is provided by Thioflavin T (ThT) fluorescence assay, where the emission intensity of the mixture PEP‐1 /ThT is considerably higher than that of the free ThT (Figure S7). [ 6c , 6d ] To gain insights into the aggregate morphology formed by PEP‐1 at neutral pH, atomic force microscopy (AFM) studies on mica were conducted. As shown in Figure 1 c , entangled nanofibrillar structures with a regular height of 3.2±0.2 nm and lengths of several micrometers are observed.…”

Research progress on self-assembled nanodrug delivery systems

“…In summary, peptide self-assembled nanosystems are widely used in drug delivery due to their multiple functions, such as high drug loading, high bioavailability, long-term efficacy, targeting, stimulation response, and cell transmembrane. 74,75…”