COMBINED APPROACH OF NMR AND MOLECULAR-DYNAMICS WITHIN A BIPHASIC MEMBRANE MIMETIC - CONFORMATION AND ORIENTATION OF THE BRADYKININ ANTAGONIST HOE-140

The conformation of the highly potent bradykinin antagonist Hoe 140 (D-Arg(0)-Arg(1)-Pro(2)-Hyp(3)-Gly(4)-Thi(5)-Ser(6)-D-Tic(7)-Oic(8)-Arg(9)) in a membrane-like surrounding was determined via NMR spectroscopy in SDS micelles and restrained molecular dynamics (MD) simulations in the novel biphasic membrane mimetic H2O/CCl4. The conformation is characterized by a beta II'-turn and a beta II-turn comprising residues 6-9 and 2-5, respectively, with the three arginine side chains anchored in the water phase and the rest of the molecule positioned in the hydrophobic phase. Selective solvation of the hydroxylated amino acids Hyp(3) and Ser(6) was examined by radial distribution functions, and both the orientation and the dynamics at the interface were analyzed by calculating the time course and the probability distribution of diagnostic atoms relative to the density profile of H2O/CCl4. Additional simulations were performed with all ionizable groups treated as charged to demonstrate the unfolding in pure H2O and the reorientation of Hoe 140 in the biphasic system after completely embedding the refined conformation in the apolar phase.