On the Nanoscale Interactions and the Self-Assembly of Recombinant Proteins and Hybrid Nanostructures: an AFM Study

Abstract

The study presented in this Thesis is focussed on the characterization and the design of new polymeric materials, taking inspiration from the Nature. Here, new hybrid architectures in which adhesive and elastic proteins coexist with inorganic or cellulosic surfaces, or where ligand capped metal nanoclusters self-assemble in monolayer films, are investigated.

Genetic engineering is used to produce new synthetic fusion proteins having specific functionalities starting from microbes. The particle self-assembly is indeed inspired on the symmetrical and directional arrangement of natural architectures such as globular proteins and viral capsids.

The study is fundamental and performed at nanoscale level. Single molecular interactions on surfaces are analysed as well as the structure and the conformation of individual fusion proteins. The self-assembly process of protein films is deeply studied as well as the stiffness and elastic modulus of self-assembled silver nanocluster composite films.

The candidate proteins for making biohybrids are hydrophobins, cellulose binding modules and resilins. Hydrophobins (HFB), with their unique assembly mechanism, are well known for their hydrophobic patch, that strongly bind to hydrophobic surfaces. Cellulose binding modules (CBMs), turned out to be highly interesting domains for their binding affinity to their primary substrate, the cellulose. On the other hand, resilin, for its ability to dissipate energy upon tensile stress, could find use as a sacrificial bond in high strength materials.

Atomic force microscope (AFM) is here used for detecting the binding and interaction forces between proteins and surfaces. For the resilin, this such powerful tool is also used to characterize the length of the biopolymer under different environments, upon stretching. AFM was also employed for determining the elastic modulus of the nanocluster monolayers. According to the results achieved, HFBI ranged a quite high adhesion force value near 100 pN on the chosen hydrophobic surfaces, whereas the CBMs reported a binding affinity for different kind of cellulosic surfaces between 40-50 pN. The silver nanoclusters ligand-capped films revealed an elastic modulus value around 20 GPa.

The Thesis sheds light on the importance of replacing plastic materials with new bio hybrids for a more sustainable approach, in an age where the ecosystem risks to be compromised by pollution and not biodegradable waste.