Tuning the Solution Self-Assembly of a Peptide-PEG (Polyethylene Glycol) Conjugate with alpha-Cyclodextrin.

Abstract

Cyclodextrins are saccharide ring molecules which act as host cavities that can encapsulate small guest molecules or thread polymer chains. We investigate the influence of alpha-cyclodextrin (αCD) on the aqueous solution self-assembly of a peptide-polymer conjugate YYKLVFF-PEG3K previously studied by our group [Castelletto et al., Polym. Chem., 2010, 1, 453-459]. This conjugate comprises a designed amyloid-forming peptide YYKLVFF that contains the KLVFF sequence from Amyloid β peptide, Aβ16-20, along with two aromatic tyrosine residues to enhance hydrophobicity as well as polyethylene glycol PEG with molar mass 3000 g mol-1. The conjugate self-assembles into β-sheet fibrils in aqueous solution. Here we show that complexation with αCD leads instead can produce free-floating nanosheets in aqueous solution (with a β-sheet structure). The transition from fibrils to nanosheets is driven by an increase in the number of αCD molecules threaded on the PEG chains, as determined by 1H NMR spectroscopy.These findings point to the use of cyclodextrin additives as a powerful means to tune the solution self-assembly in peptide-polymer conjugates and potentially other polymer/biomolecular hybrids.