Construction of alpha-helix peptides with beta-cyclodextrin and dansyl units and their conformational and molecular sensing properties.

In order to apply de novo peptide design to molecular sensing, we designed and synthesized a-helical peptides with beta-cyclodextrin (beta-CDx) as a binding site and a dansyl unit (Dns) as a fluorescence sensing site. The conformational and molecular sensing properties of the peptides with beta-CDx and Dns in various positions were investigated. Circular dichroism and fluorescence measurements revealed that beta-CDx and Dns form intramolecular complexes which depend on their positions in the peptides. In the 17 residual peptides named EK3 and EK3R, in which beta-CDx and Dns were introduced at the fourth and the eighth positions (EK3) or at the eighth and the fourth positions (EK3R), Dns was deeply included in the CDx cavity and formed a more stable self-inclusion complex with CDx than in the peptides EK6 and EK6R, in which these moieties were at the eighth and the fifteenth positions or at the fifteenth and the eighth positions, respectively. The stability of the self-inclusion complex between beta-CDx and Dns controlled the a-helix structure as well as the binding and sensing abilities for the exogenous guests. These results demonstrate the usefulness of peptide tertiary structure for arranging CDx and other functional units, and suggest that this approach is important in the development of a new type of CDx-based sensory system.