Coupled Plasmon Waveguide Resonance Studies of Agonist/Antagonist Binding to the Human δ-Opioid Receptor Provide New Structural Insights Into the Three-State Model for Receptor-Ligand Interactions

Abstract

Traditional methods in pharmacology characterize a ligand by its binding to a receptor and/or the subsequent second messenger response. No information on the direct conformational changes of the receptor in response to the ligand is obtained. Using a new method, coupled plasmon-waveguide resonance spectroscopy, structural changes of the human δ-opioid receptor immobilized in a lipid bilayer accompanying the binding of agonists and antagonists have been investigated. This highly sensitive technique directly monitors mass density, conformation, and molecular orientation changes occurring in anisotropic thin films. The extent of conformational change versus the amount of ligand allows determination of binding constants that are in good agreement with published values for the same ligands.