Peptide drug candidates for pathogenic amyloids

Abstract

Amyloid fibrils are very stable, ordered cross-β structured, resistant to protease degradation, proteinaceous composits. All amyloids have different peptide/protein sequences although they express similar structural properties. Some of amyloids possess advantageous functionalities such as protection, cell-cell communication, protein storage. However, most of amyloids are associated with various severe diseases such as neurodegenerative diseases. Although amyloids follow similar formation pathway, pathogenic amyloids are challenging since their formations are supported with secondary pathways. Up to now, there were several therapeutic approaches that are only effective in symptoms of disease conditions by masking or slowing down the symptom developments. Nonetheless, different approaches are developed for inhibiting amyloid aggregation. Today, most of the strategies are aiming to inhibit secondary nucleation, which is not fully understood yet. So, such approaches can be faced with lots of challenge in terms of secondary nucleation kinetics and formation mechanism. Thus, inhibition of monomeric amyloid units, which are developed into amyloid aggregates, can be another novel approach for halting disease-condition developments. In this thesis, candidate ligand peptides that cease aggregation of huntingtin, α-synuclein and amyloid-β were selected by using different types of display systems, which are bacterial surface display, yeast surface display and phage display. The monomeric amyloid units of these proteins were expressed on surfaces of bacterial cells and yeast cells in order to expressing monomeric units with a proper folding and avoiding aggregation after expression without interacting with each other. Candidate ligand peptides were selected against neurodegenerative amyloids by M13 phage display library. First, M13 phage display library was tried to be produced from using wild type M13 bacteriophage by basic cloning methods as well as commercially available M13 phage display library kit was used for peptide selection since the minor coat protein pIII of M13 is widely used for peptide display and ligand peptide selection studies. Thus, 12 amino acid-long peptides displayed on the minor coat protein pIII were selected against neurodegenerative amyloids for inhibiting protein aggregation purpose in the very first step of aggregation pathway.