Sequence-Dependent Bioactivity and Self-Assembling Properties of RGD-Containing Amphiphilic Peptides as Extracellular Scaffolds

Abstract

Cell adhesion is a fundamental biological process involved in a wide range of cellular and biological activity. Integrin−ligand binding is largely responsible for cell adhesion with an extracellular matrix, and the RGD sequence is an epitope in ligand proteins such as fibronectin. The extracellular matrix consists of fibrous proteins with embedded ligands for integrins. Such a biological architecture has been reconstructed for biochemical, pharmaceutical, and biomaterial studies using artificial supramolecular systems to reproduce cell adhesion functionality, and fiber-forming self-assembling peptides containing RGD are one such promising material for this purpose. In this study, using RADA16 as a model fiber-forming peptide, a series of RGD-containing variants have been synthesized by the replacement of one alanine with glycine at different positions, in which all the variants consist of identical amino acid components. The position of the RGD unit influenced the supramolecular self-assembly of the amphiphilic peptide to inhibit β-sheet formation (A6G) or twist the molecular alignment in β-sheet-type assemblies (A10G and A14G). Furthermore, A10G and A14G formed assembled nanofibers, which afforded hydrogels with higher viscoelasticities than other RGD-containing variants. In contrast to A10G and A14G, which exhibit substantial cell adhesion functionality, the cell adhesion efficiencies of the other RGD-containing variants were significantly reduced. This suggests that the higher order structure could strongly influence the cell adhesion functionality of RGD-containing supramolecular nanofibers.

Self-Assembled Peptide Nanostructures for ECM Biomimicry

“…In this manner, it was possible to tailor the differentiation of human mesenchymal stem cells, with adipogenesis being favored by softer gels with lower concentrations of RGD. In another recent work, RGD-modified hydrogels were obtained by simply changing an alanine with glycine in different positions of the well-known gelator peptide RADA16 [59]. This study showed that the substitution position has a great impact on the gelation ability and properties of the system, as well as on the cell adhesiveness.…”

Current Progress in Cross-Linked Peptide Self-Assemblies

“…In many cases, peptide fibers become cell adhesive if an RGD sequence is introduced to the peptide sequence exposed to aqueous media. For example, the cell adhesive peptide amphiphile [ 21 ], Fmoc–FF-based peptide fibers [ 39 ], peptide fibers with RADA repeat [ 57 ], and peptide fibers with β -heparin structure [ 66 ] have been prepared by the introduction of an RGD sequence. However, the position of introducing the RGD sequence can affect cell adhesivity.…”

“…However, the position of introducing the RGD sequence can affect cell adhesivity. When the RGD sequence is introduced to peptide fibers having a RADARADARADARADA sequence as a self-assembly unit by replacing RAD with RGD, peptide fibers containing the RGDARADARADARADA sequence show weaker cell adhesivity compared to peptide fibers containing the RADARADARADARGDA sequence [ 57 ]. As the rigidity of peptide fibers and rearrangement of monomer peptide units influence the viability and differentiation of cells cultured on the peptide fibers, the dynamic nature of peptide fibers has been investigated in detail.…”

Self-assembly of Amphiphilic Peptide in Phospholipid Membrane

“…Peptide-based self-assemblies in aqueous media are an attractive platform capable of imparting various bioactive functions by controlling the amino acid sequence. Indeed, a lot of biomaterials with superb functions have been realized by using selfassembling peptides [10][11][12][13][14][15][16][17][18][19][20]. In this work, to study self-assembly of peptides at a bilayer membrane, we designed an amphiphilic molecule Lipid-(RADA)2.…”

“…(RADA)2 peptide has alternating hydrophilic (R and D) and hydrophobic (A) amino acid residues [21]. Such an alternating sequence between hydrophilic and hydrophobic amino acid residues is known to be favorable to form a β-sheet self-assembly [18][19][20]. The alkyl chains with a fluorescent group were attached to (RADA)2 peptide as an anchoring unit into the phospholipid membranes and for direct observation under a fluorescence microscopy.…”