The Effect of Peptide Length on Liquid Crystal Formation of Single Charged Bundlemers

• Olivia King, Biomedical Engineering, Saint Louis University

• Darrin Pochan, Material Science and Engineering, University of Delaware

Bundlemers are computationally designed, self-assembling, homotetrameric coiled-coil peptide nanoparticles composed of repeating heptads. Bundlemers with positive single-charged sequences, 29 amino acids in length, exhibit well-defined and ordered structure exhibiting liquid crystalline behavior. Bundlemer self-assembly follows Onsager’s theory, which requires long, narrow rods for liquid crystal formation. Although individual bundlemers are short, stacking extends the hydrophobic core, allowing for liquid crystal formation. Experimentation with shortened bundlemers, 29 to 22 amino acids in length through the removal of one heptad, shows that structural order can be preserved. Shortened sequences maintain liquid crystalline properties by end-to-end stacking and have improved synthetic efficiency. Although shorter sequences still form alpha helical coiled coils, trimmed versions, 20 amino acids in length through the removal of the N-terminus, do not, indicating the importance of the N-terminus in retaining structural integrity. Circular dichroism spectroscopy demonstrated that the results were consistent with coiled coil structures, and polarized optical microscopy allowed for visual verification of liquid crystalline nanostructure. Further, self-assembly and liquid crystal formation were studied with small-angle x-ray scattering and polarized optical microscopy. Through continued experimentation, the minimum length allowed for coiled coils can be found to determine the shortest bundlemer that maintains coiled coil integrity. Additionally, future work could include comparisons of liquid crystal behavior with mixed charged bundlemers.