Conformational diversity of [D-Pen2,D-Pen5]enkephalin as studied by magic-angle spinning liquid-crystal NMR spectroscopy and multiconformational analysis

The conformation of biologically active [D-Pen(2),D-Pen(5)]enkephalin (DPDPE) has been studied by liquid-crystal NMR spectroscopy employing magic-angle spinning (MAS) two-dimensional methodology and by computer-assisted multiconformational analysis. The NMR structural parameters of DPDPE were obtained in a CsPFO (cesium perfluorooctanoate) liquid-crystal. The NMR structural information was acquired in the anisotropic environment based upon the vicinal coupling constant of (3)J(HNCalphaH) and the H-1-H-1 ROE factors obtained under the MAS condition. These data were submitted to multiconformational analysis based on the ECEPP/2 potential energy function and the Metropolis Monte Carlo simulation. As a result of the energy calculation, four conformers an obtained for DPDPE which are considered to exist in the anisotropic environment. The major contribution is determined among these probable conformers in the liquid-crystal medium. Moreover, it is suggested from the NMR multiconformational analysis that the D-Pen(5) residue, the C-terminal "address" segment, is responsible for the conformation of the "message" segment (N-terminal tetrapeptide sequence). The conformational flexibility is discussed for the spatial arrangement of the Tyr(1) and Phe(4) aromatic rings in the message segment of the bioactive conformation in relation to the activity of DPDPE.