Differential supramolecular organisation of Fmoc-dipeptides with hydrophilic terminal amino acid residues by biocatalytic self-assembly

The study of enzymatically triggered self-assembly of aromatic peptide amphiphiles has become increasingly popular in recent years and has lead to a variety of nanoscale architectures. As hydrophobic interactions have been recognised as a major driving force in their self-assembly, typically, the peptide components are found to be hydrophobic in nature, containing aromatic or aliphatic amino acid residues. In this article, we use subtilisin triggered self-assembly of four closely related Fmoc-dipeptide amphiphiles with terminal hydrophilic amino acid residues, YT, YS, YN and YQ, in order to introduce a new functionality to the self-assembled systems, and determine the influence of each amino acid side chain. We use microscopy techniques, rheology, fluorescence, FTIR and CD to demonstrate differences in molecular assembly, mechanical properties and nanoscale architecture as a direct result of the subtle molecular variance of each system. We demonstrate that the amino acid side chain in position two directly affects the molecular packing abilities in the supramolecular structure, with YT, YS and YN forming nanoscale fibres with mechanical properties being linked to the functionality of the amino acid side chain, and YQ forming spherical structures due to steric effects associated with the glutamine side chain prohibiting the adoption of the typical pi-beta assembly.