"Belt and braces": a peptide-based linker system of de novo design.

A new self-assembling peptide-based linker is described. The system comprises three leucine-zipper sequences of de novo design: one peptide, "the belt", templates the co-assembly of the other two-half-sized peptides, "the braces". These basic features were confirmed by circular dichroism spectroscopy and analytical ultracentrifugation: when mixed, the three peptides reversibly formed a predominantly helical and stable 1:1:1 ternary complex. Surface plasmon resonance experiments demonstrated assembly of the complex on gold surfaces, while the ability of the system to bring together peptide-bound cargo was demonstrated using colloidal gold nanoparticles. In the latter experiments, the nanoparticles were derivatized with the brace peptides prior to the addition of the belt. Transmission electron microscopy images of the resulting networks revealed regular approximately 7 nm separations between adjacent particles, consistent with the 42-amino acid helical design of the belt and braces. To our knowledge, belt and braces is a novel concept in leucine-zipper assembly and the first example of employing peptides to guide nanoparticle assembly.