Power struggles between oligopeptides and cyclodextrin vesicles

Abstract

Stimulus responsive supramolecular assemblies were constructed by decorating the surface of β-cyclodextrin vesicles (CDVs) with β-sheet forming oligopeptides. Three octapeptides were used to coat the CDVs: adamantane-(leu-glu)₄ (1), adamantane-PEG₄-(leu-glu)₄ (2) and (adamantane-PEG₄)₂-(leu-glu)₄ (3). The adamantane moiety ensured the binding of the peptides at the surface of the CDVs. At pH 7.2, all the peptides typically adopt a random coil secondary structure. Upon acidification to ∼pH 5, however, a reversible transition to well-defined β-sheet structures was observed. The pH at which this transition occurred was found to be influenced by the PEG₄-spacer and the number of adamantane residues conjugated to the octapeptide hybrids. The structural rearrangement of the peptide backbone was found to induce a morphological transition of the entire assembly. For the peptide (1)–CDV assembly a reversible transition to fiber like structures was observed, whereas bundles of aggregated fibers were present in the peptide (2)–CDV assembly. Upon adding peptide (3) to the CDVs, the structural integrity of the CDVs was lost. The peptide (1)–CDV assembly shows promise as a delivery device due to the pH-induced vesicle-to-fiber transition, resulting in a release of its cargo from the aqueous interior of the CDVs. The amount of released cargo could be controlled as a function of pH and peptide concentration.