Direct observation of morphological transformation from twisted ribbons into helical ribbons

Abstract

We report on the direct observation of a nanostructural transformation from a twisted ribbon to a helical ribbon in supramolecular assemblies of peptide amphiphiles. Using cryogenic electron microscopy, a peptide amphiphile molecule containing aromatic residues was found to first assemble into short twisted ribbons in the time range of seconds, which then elongate in the time scale of minutes, and finally transform into helical ribbons over the course of weeks. By synthesizing an analogous molecule without the aromatic side groups, it was found that a cylindrical nanostructure is formed that does not undergo any transitions during the same time period. The study of metastable states in peptide aggregation can contribute to our understanding of amyloid-related diseases, such as Alzheimer's disease.

Figure 1

CryoTEM of PA 1 a) forming short twists 30 seconds after the water was added to PA 1 after being molecularly dissolved b) long twisted ribbons when completely dissolved in water c) a twisted ribbon (white arrow) transforming into a helix (black arrow) and d) helical ribbons after being aged at 25°C for one month. Schematic illustrations are shown in part e).