Abstract:

Synthetic matrices provide powerful tools for dissecting molecular interactions involved in the organization of the extracellular matrix (ECM), establishment of cell axis polarity, and suppression of neoplasticity in pre-cancerous endothelial cells. Collagen is the most abundant protein in extracellular matrix. A de novo approach is essential for the synthesis of collagen matrices which can have a broad impact on the understanding of matrix biology and our capacity to construct safe and medically useful biomaterials. Conventionally, the ECM has been studied by an analytical "top-down" approach, where the individual components of the matrix are first isolated and then characterized to explore their biochemical and functional properties. Since native collagen is difficult to modify and can engender pathogenic and immunological side effects, its application on tissue regeneration is limited. Therefore, we attempted to synthesize artificial collagen directly through small organic molecule recognition. The collagen-like peptides possess various benefits such as being clean, programmable, and easy to modify; therefore, in recent years, they have been used as ideal substrates for the synthesis of collagen nanomaterials. The self-assembly of collagen-like peptides is mainly driven by various non-covalent interactions such as electrostatic attraction, π-π stacking, and metal coordination. This renders a difficulty in the rational design of uniform nanostructures from short synthesized peptides and demands a novel strategy. To date, small organic molecules have been rarely used for the self-assembly of collagen-like peptides. In the present study, we attempted to use the small organic molecules for the combined supramolecular self-assembly of collagen-like peptides. Initially, the collagen-like peptides, (POG)₆ and (POG)₈, synthesized by the solid-phase synthesis technique, were both modified chemically using 4, 4'-methylene bis(phenyl isocyanate) to obtain the collagen-like hybrid peptides, AP₆ and AP₈, respectively. Phenyl isocyanate contributes to the formation of potential weak forces, such as hydrogen bonds and π-π stacking at the N-terminal regions of the collagen-like hybrid peptides. The purity and molecular weight of the collagen-like hybrid peptides were analyzed using analytical high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF), respectively. The stability of AP₆ and AP₈ triple helices was analyzed by circular dichroism (CD) spectroscopy. The small organic molecule 4, 4'-methylene bis(phenyl isocyanate) promoted the unfolding of (POG)₆ and increased the melting temperature (T_m) of (POG)₈ from 37.7 to 58.8 ℃to form a triple helix. The hydrodynamic radii of collagen-like hybrid peptides were measured by dynamic light scattering (DLS). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to analyze the morphology of the aggregation states. AFM results showed that the collagen-like hybrid peptides, AP₆ and AP₈, formed nanofibers spontaneously. Consistent with the AFM results, TEM showed that the AP₆ and AP₈ collagen-like hybrid peptides also formed nanofiber structures. The formation of stable complexes was attributed to the presence of multiple weak interactions such as hydrogen bonding, π-π stacking, and hydrophobic interactions. In the present study, we demonstrated that the chemical modification of collagen-like polypeptides at the N-terminus via the small organic molecule, 4, 4'-methylene bis(phenyl isocyanate), promoted the intramolecular and intermolecular assembly of collagen-like peptides. A simple and effective strategy has been developed in this study to promote the self-assembly of collagen-like peptides.

Key words: Collagen-like peptide, Triple helix, Phenyl isocyanate, Weak interaction, Self-assembly, Nanofibers, Nano materials