The self-assembly in aqueous solution of the alanine-rich peptide A12R2 containing twelve alanine residues and two arginine residues has been investigated. This oligomeric peptide was synthesized via NCA-polymerization methods. The surfactant-like peptide is found via FTIR to form antiparallel dimers which aggregate into twisted fibrils, as revealed by cryogenic-transmission electron microscopy. The fibril substructure is probed via detailed X-ray scattering experiments, and are uniquely comprised of twisted tapes only 5 nm wide, set by the width of the antiparallel A12R2 dimers. The packing of the alanine residues leads to distinct “β-sheet” spacings compared to those for amyloid-forming peptides. For this peptide, β-sheet structure coexists with some α-helical content. These ultrafine amyloid fibrils present arginine at high density on their surfaces, and this may lead to applications in nanobiotechnology.
