Self-assembly of computationally designed peptide coiled-coil bundles

30 amino-acid peptides were computationally designed to assemble into homotetrameric coiled-coil bundles in a parallel arrangement. The N-termini of peptides were modified by cysteine or a non-natural maleimide functional group, respectively.  Parallel coiled-coil bundles were linked together by thiol-Michael ‘click’ conjugation reaction to form bundle chains. Because all four N-termini of the constituent peptides are displayed from the same bundle end, only dimer bundle chains are possible by design making monodisperse chains a possibility when linking them together in an end-to-end fashion. The difference between the designed parallel peptide arrangement and undesired antiparallel bundle structure can be proved by Förster resonance energy transfer (FRET) experiments. The distance between the FRET pair on the two kinds of bundles is different, which leads to different fluorescence intensities. Small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) are used to characterize the size and shape of chains. The liquid crystal behavior of parallel bundles will be studied under polarized optical microscopy.