Organization of designed nanofibrils assembled from α-helical peptides as determined by electron microscopy

Abstract

Self-assembling peptides present attractive platforms for engineering materials with controlled nanostructures. Recently, an α-helical fibril forming peptide (αFFP) was designed that self-assembles into nanofibrils at acid pH. Circular dichroism spectroscopy, electron-microscopy and x-ray fibre diffraction data showed that the most likely structure of αFFP fibrils is a five-stranded coiled coil rope. In the present study, scanning transmission electron microscopy (STEM) was used to improve our understanding of the αFFP fibril structure. The measurements of fibril mass per length suggest that there are ten α-helices in transverse sections of the fibrils. Based on the known data, it is proposed that a predominant fibrillar structure of αFFP is a dimer of α-helical five-stranded protofilaments wrapped around a common axis. It is shown that these structures have an axial dimension of 58 ± 16 nm and a width of 4 ± 1 nm. A small number of thin fibrils is also observed in the negative stained preparation and STEM images. The thin fibrils may correspond to the single protofilament. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.