Interactions of cyclodextrins with aromatic amino acids: A basis for protein interactions

Cyclodextrins (CyD) have proven effects on the stability of proteins and can be used in the formulation of aggregation prone therapeutic proteins. This effect stems from specific interactions between the CyD (preferably β-CyD) and solvent exposed amino acid residues. Here the interaction with hydrophobic aromatic amino acid residues stands out and the interaction between CyDs and these amino acid residues holds the key to understanding the observed effects, which CyDs exerts on proteins and peptides. Here we present a comparative study of the interactions between free and peptide bound aromatic amino acids and their derivatives with α, β and γ-CyDs using NMR spectroscopy. We propose a novel, quantitative means of assessing the penetration depth of guest molecules in CyD cavities, the penetration gauge Π, and apply it to the observed interaction patterns from ROESY NMR spectra. We demonstrate that the penetration depths of the aromatic rings within the CyDs rely highly on the nature of the remainder of the guest molecule. Thus the presence of charges, neighboring amino acids and the specific positioning on the surface of a protein highly influences the penetration depth and geometry of guest-CyD interactions.