Peptide Self-Assembly from the Molecular to the Macroscopic Scale at Standard Conditions

Abstract

This dissertation attempts to address the problem of how to prepare protein-based materials with the same level of order and precision at the molecular level similar to the structures we find in nature. It is divided into two parts focusing on feedstock and processing. Part one is devoted to discussing the use of agricultural proteins as a feedstock for material production. Particularly, it focuses on the effect of hydrogen bonding, or lack thereof, between proteins as mediated by hydration or plasticization. The effect of varying plasticizer (glycerol) levels on mechanical properties of a series of proteins is discussed in the context of primary and secondary structure of these proteins. We have found that the extent to which a protein can be plasticized is dependent on its molecular and higher order structure and not simply molecular weight, as it was often assumed in previous studies.

The second part of the dissertation focuses on the study of self-assembly as a way to make useful peptide-based materials. There are major efforts underway to study protein self-assembly for various medical and industrial reasons. Despite huge progress, most studies have focused on nanoscale self-assembly but the crossover to the macroscopic scale remains a challenge. We show that peptide self-assembly into macroscopic fibers is possible in vitro under physiological conditions. We characterize the fibers and propose a mechanism by which they form. The macroscopic fibers self-assemble from a combination of β- and α-peptides and are similar to other naturally-occurring systems in which templated self-assembly is used to create functional peptide materials. Finally, the ability to control macroscopic properties of the fiber by varying the ratio of constituent peptides is demonstrated.

Owing to the richness of the amino acid building blocks, peptides are highly versatile structural and functional building blocks. The ability to extend and control peptide self-assembly over multiple length scales is a significant leap toward incorporating peptide materials into dynamic systems of higher complexity and functionality.