H-1 NUCLEAR-MAGNETIC-RESONANCE DETERMINATION OF THE MEMBRANE-BOUND CONFORMATION OF SENKTIDE, A HIGHLY SELECTIVE NEUROKININ-B AGONIST

Senktide is a highly specific and potent analog of neurokinin B, the n atural ligand of the tachykinin receptor NK-3. The membrane-bound conf ormation of senktide, interacting with negatively charged membrane ves icles composed of perdeuterated phosphatidylcholine and phosphatidylgl ycerol (70:30), has been investigated using two-dimensional transferre d nuclear Overhauser effect spectroscopy (TRNOESY). The occurrence of an N-methylated phenylalanine in the peptide's sequence induces a cis- trans-isomerisation of the corresponding peptide bond which is slow on the chemical-shift scale. NMR data indicate a much stronger membrane affinity of the trans isomer, allowing the determination of a highly r esolved membrane-bound conformation using distance geometry and energy minimization. The membrane-bound backbone conformation of several res idues is found to be close to a left-handed helix, certainly due to th e presence of nonnatural residues (succinylated N-terminal, N-methyl-p henylalanine) as well as a glycine. The results are discussed in the c ontext of a possible biological relevance of the membrane-bound confor mation, in terms of the affinity and specificity of this neuropeptide.