Amphiphilic Peptides with Flexible Chains for Tuning Supramolecular Morphologies, Macroscopic Properties and Biological Functions

Fibrous aggregates of polypeptides linked by β-sheet assemblies are important supramolecular morphologies in biology, chemistry and materials science. β-Sheet-forming synthetic amphiphilic peptides afford hydrogels that have been used as biomaterials for cell culturing and differentiation media. For their bio-related applications, tuning the mechanical and biological properties of the amphiphilic peptides is critically important, and this has mainly been done by modulating the side chain structures. In this review, the effects of flexible alkylene chains inserted in the interior sequence of amphiphilic peptides on supramolecular morphologies and biological properties are described. Exchange of glycine for alanine residues influences the self-assembling structures and mechanical properties depending on the sites substituted. Despite increased conformational flexibility due to the alanine-to-glycine substitution, insertion of glycine at the center of the peptide molecule forms a hydrogel with enhanced mechanical stiffness. Extending the length of the central alkylene chains further enhanced the stiffness of hydrogel. Furthermore, insertion of an alkylene chain in the peptide backbone allows the endowment of dynamic properties such as thermal gel-to-sol transition, while the cell adhesive properties are reduced on insertion of relatively long alkylene chains. The versatility of alkylene-chain insertion into a polypeptide main chain for tuning, chemical, physical and biological properties is reported.