Investigation of supramolecular assemblies based on de novo coiled coil peptidic scaffolds

Abstract

The ability of peptides to self-assemble into defined supramolecular structures has been of interest to scientists for decades. The expansion of our understanding of the relationships between amino acid sequence and assembly has been accompanied by a growing number of supramolecular structures. There are still, however, some challenges that must be overcome for these materials to be suitable for real-world applications. In particular, the development of simple scaffolds that can self-assemble into stable and ordered structures in a controllable and predictable manner must continue to be pursued. In this context, the results presented in this thesis reports on the development of new, simple and robust coiled-coil peptidic scaffolds that can assemble into different micro- and nanoscale structures. The highlight of this work is the development of a simple 29-mer coiled-coil Cy5 dye conjugate that undergoes stimuli-triggered aggregation resulting in the formation of microscale membranes and rods under acidic and neutral pH conditions, respectively. Spectroscopic and electron microscopy analyses revealed that the presence of Cy5 at the N-terminus was crucial for the formation of high aspect ratio assemblies, whereas peptide sequence governed responsiveness towards pH and structural morphology. Subsequently, a series of newly designed sequences were synthesized and tested to further understand the underlying driving forces for assembly, and to manipulate peptide stability and self-assembly. The first redesigned series aimed to study the impact of substitution of Cy5 with analogous but simpler aromatic systems. It was found that only a compromise between hydrophobicity, charge, and size of the aromatic moieties leads to high order assemblies. In the second redesigned series, the substitution of residues within the hydrophobic core with a fluorinated amino acid or a natural analogue were performed in an attempt to improve peptide stability. The findings showed that the nature and the packing of the side-chains in the helical core were critical for peptide stability and for pH-sensitive aggregation. The final redesign aimed to study the influence of residues placed in solvent exposed positions of the coiled-coil motif on peptide conformation and stability. The results demonstrated that the nature of substitution does not affect the secondary conformation. However, peptides possessing an overall positive net charge exhibit higher thermal stability. The peptides presented here enable the development of pH-sensitive supramolecular structures, which have potential applications in biomedicine or material sciences.