Nucleobase-directed amyloid nanotube assembly

Cytosine nucleobases were successfully incorporated into the side chain of the self-assembling amyloid peptide fragment HHQALVFFA to give ccAQLVFFA. At a pH range of 3?4, where cytosine is expected to be partially protonated, small-angle X-ray scattering analyses revealed the nucleobase peptide assembles to be well-defined nanotubes with an outer diameter of 24.8 nm and wall thicknesses of 3.3 nm. FT-IR and X-ray diffraction confirmed β-sheet-rich assembly with the characteristic cross-β architecture of amyloid. The β-sheet registry, determined by measuring ¹³CO-¹³CO backbone distances with solid-state NMR and linear dichroism, placed the cytosine bases roughly perpendicular to the nanotube axis, resulting in a model where the complementary interactions between the cytosine bases increases β-sheet stacking to give the nanotube architecture. These scaffolds then extend the templates used to encode biological information beyond the nucleic acid duplexes and into covalent networks whose self-assembly is still defined by a precise complementarity of the side-chain registry.