Nanostructural Transformation of Photo-Crosslinking Peptides Visualized by In Situ Liquid-Phase Transmission Electron Microscopy

Peptide self-assembling nanostructures based on diphenylalanine (FF) can have organized beta-sheet secondary structures that can result in the formation of spheres, cylinders, and tubes depending on the strong interaction of phenyl groups between adjacent derivatives. Due to the structural stability and biocompatibility of FF, it has been widely used in biological applications such as drug delivery and tissue regeneration, and its biological significance has motivated numerous research fields including self-assembly and functional biomaterials with mechanical, piezoelectric, and semiconductor properties. Up to now, the conventional bulk solution characterization approaches have been used for the majority of studies on the kinetics, dynamics, and phase transitions of FF assemblies, however, these technologies lack a direct understanding of the dynamics and morphology. In this study, short peptides were modified using a tyrosine-mediated crosslink to adopt the characteristic of the resilin of the dragonfly, vinegar fly, and beetle that photooxidation-reduction can occur and alter the antiparallel structure to generate 1D nanostructure. In this context, protein-mimetic structural evolution was investigated. Through the use of liquid-phase transmission electron microscope (LP-TEM) imaging, the structural conversion of 1D to 3D structures by peptide cross-linking was demonstrated. This result suggests that because of their packing sensitivity and geometrical limitations, the nature-protein motion should be studied to acquire insights for developing peptide-based materials. Furthermore, the observation of the assembly and dynamics of FFs in real-time with LP-TEM would enable us to understand the paths for assembly and phase transformations.