Manifold of self-assembly of a de novo designed peptide: amyloid fibrils, peptide bundles, and fractals.

We report that a peptide with the sequence of EGAGAAAAGAGE can have different aggregation states, viz. , amyloid fibrils, peptide bundles, and fractal assembly under different incubation conditions. The chemical state of the Glu residue played a pivotal regulating role in the aggregation behavior of the peptide. The mechanism of the fractal assembly of this peptide has been unraveled as follows. The peptide fragments adopting the beta-sheet conformation are well dispersed in alkaline solution. In the buffer of sodium bicarbonate, peptide rods are formed with considerable structural rigidity at the C- and N-termini. The peptide rods undergo random trajectory in the solution and form a fractal pattern on a two-dimensional surface via the diffusion-limited aggregation process.