Self-Assembling Behavior of pH-Responsive Peptide AK without End-Capping.

A short self-assembly peptide AK (HN-AAAAAAK-OH) with unmodified N- and C-terminus was designed, and the charge distribution model of this short peptide at different pH was established by computer simulation. The pH of the solution was adjusted according to the model and the corresponding self-assembled structure was observed using a transmission electron microscope (TEM). As the pH changes, the peptide will assemble into blocks or nanoribbons, which indicates that the AK peptide is a pH-responsive peptide. Circular dichroism (CD) and molecular dynamics (MD) simulation showed that the block structure was formed by random coils, while the increase in β-turn content contributes to the formation of intact nanoribbons. A reasonable explanation of the self-assembling structure was made according to the electrostatic distribution model and the effect of electrostatic interaction on self-assembly was investigated. This study laid the foundation for further design of nanomaterials based on pH-responsive peptides.