Orientation and conformation of met-enkephalin in a liquid crystal as studied by magic-angle- and near-magic-angle-spinning two-dimensional NMR spectroscopy

The orientation and conformation of a neuropeptide, Met-enkephalin (Tyr-Gly-Gly-Phe-Met), have been determined in liquid crystal by NMR spectroscopy after exploiting magic-angle- and near-magic-angle-spinning (MAS/NMAS) two-dimensional methodology. A lyotropic nematic phase was used as a solvent, which was formed from cesium perfluorooctanoate and water. The determination of conformation and orientation was based on the measurement of H-1-H-1 dipolar couplings obtained at NMAS condition and H-1-H-1 ROE factors obtained at MAS condition. These data were used in target functions in the minimization process of pseudoenergy analysis, leading to the conformation and preferred orientation in the anisotropic environment The results indicate that the conformation, is in a folded form like a beta turn and that the molecule is preferentially oriented along the direction perpendicular to the line connecting two phenyl rings in Tyr and Phe.