Lysine functionalised amyloid fibrils: the design and assembly of a TTR1-based peptide

Non-core residues can affect the formation and protofilament packing of fibrils assembled from short peptide sequences. These residues are of interest in understanding amyloid diseases and in the design of self-assembling peptide materials with a cross-beta core, where the assembly process should be reproducible and functional groups accessible on the fibril surface. In this study, the well characterised TTR1 peptide, also known as TTR105-115, was functionalised with glycine and lysine residues forming the peptide TTR1-GGK, with the aim of producing a self-assembling fibril scaffold that can be functionalised following assembly. A second aim was to develop a sequence capable of fibril assembly under a wide range of solution conditions. The lysine residue was found accessible on the surface of TTR1-GGK fibrils and the C-terminal residues influenced the mature fibril width and rate of fibril assembly, as observed for other TTR1-based fibrils. The assembly of TTR1-GGK fibrils was examined for conditions of varying ionic strength (NaCl, 0-0.5 M), solution pH or in the presence of anions (NaCl, Nal, NaNO3 and NaSO4) or cations (NaCl, CaCl2, MgCl2, LiCl and KCl). The addition of salt increased the rate of TTR1-GGK fibril nucleation but decreased the rate of elongation at high salt concentrations. A combination of electrostatic and hydrophobic interactions was found to promote initial contacts between peptides. Specific ion effects were seen with chaotropic anions, which promoted fibril nucleation. The cross-beta core structure, secondary structure and morphology of TTR1-GGK fibrils were largely unaltered by the presence of salt or a range of solution pH. The length of fibrils was also maintained at the high ionic strengths tested, indicating that these fibrils may make suitable scaffolds for fibril functionalisation under a range of conditions.