Stabilization of the peptide conformation on the micellar surface

Abstract

The conformational mobility of peptide molecules plays a significant role in peptide–receptor interactions and quantitative structure–activity relationships. As a receptor mimetic system, bis(2-ethylhexyl) sodium succinate (AOT) reversed micelles containing an aqueous solution of one of the melanotrophine inhibiting factor analogues prolyl–tyrosyl–glycinamide hydrochloride in the inner cavity have been used. Two-dimensional nuclear magnetic resonance spectroscopy (NOESY) and ¹³C spin-lattice relaxation time measurements have been used to establish that the peptide molecule assumes the biologically active β_II turn conformation when it is adsorbed at the surfactant–water border. This conformation is stabilized by intramolecular H-bonding between the proline carbonyl oxygen atom and amide protons. Moreover, it has been shown that the phenyl ring of tyrosine was inserted into the AOT intermolecular cavity, which is located between the polar AOT groups and the branches of iso-octane fragments. By and large, the phenyl ring acts as a hydrophobic anchor. Reversed micelles can be regarded as providing a realistic model of the receptor.