Role of First Amino Acid on the Self-Assembly and Gelation Pathways of Beta-Sheet Forming Octa Peptides

Abstract

Self-assembling peptide hydrogels have attracted significant interest in the past decade due to their potential use in a range of applications from cell culture to tissue engineering and drug delivery. One of the key challenges when designing hydrogels for biomedical applications is the variety and types of demands placed on the materials depending on the application targeted. As a result, understanding the relationships between peptide design, self-assembly pathway and the final properties of bulk hydrogels is key to fulfil the potential of these materials. In this PhD project, a family of beta-sheet-forming self-assembling peptides was examined, with a particular focus on the role of the first amino acid in the sequence. Altering peptide sequences was found to be a useful method for adjusting the mechanical strength of hydrogels. Various techniques were employed to investigate the self-assembly, gelation propensity, and morphology of peptide hydrogels. The initial phase of the study involved designing two peptides, namely FEFKFEFK (F-pep) and LEFKFEFK (L-pep), where the first amino acid's end group was changed to F (aromatic) and L (aliphatic) to observe their impact on fibre-fibre network junctions and the resulting hydrogel properties. Subsequently, the influence of the first amino acid's side chain volume on peptide hydrogels was explored using three peptides: IEFKFEFK (I pep), VEFKFEFK (V-pep), and AEFKFEFK (A-pep), each with varying side-chain volumes. In Chapter VI of the investigation, the contributions of π-π interactions versus general hydrophobic interactions were meticulously analysed for these peptides. Two peptides, WEFKFEFK (W-pep) and YEFKFEFK (Y-pep), were designed for this purpose. The study revealed that the first amino acid in these systems can influence self-assembly across different length scales through physical interactions. Aromatic end groups showed a tendency to engage in π-π stacking interactions, resulting in stronger and more specific self-assembly. This interaction pattern produced thin, linear fibres within the hydrogel structure. Conversely, aliphatic end groups led to twisted and ribbon-like fibres, facilitating the formation of laterally stacked beta-sheets. This distinct structure resulted in a more rigid and organized hydrogel network. This finding underscores the ability of the first amino acid to govern not only the morphology of self-assembled structures but also the overall mechanical properties of the hydrogel. Additionally, peptides relying on π-π interactions tended to form dense networks due to the directional nature of these interactions, promoting high order and connectivity within the hydrogel structure. Larger side groups were found to hinder self-assembly, favouring anti-parallel structures that affected network topologies and mechanical properties. The thesis highlights the correlation between rheological characteristics and 9 peptide fibril morphology, emphasizing that manipulation of amino acid hydrophobicity and aromaticity can control self-assembly and supramolecular properties. This research contributes valuable insights for the rational design of self assembling peptide hydrogels with biomedical applications in mind.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Aline Saiani (Supervisor) & Alberto Saiani (Supervisor)