Conformational sampling of bioactive conformers: a low-temperature NMR study of 15N-Leu-enkephalin.
Conformational studies of enkephalins are hampered by their high flexibility which leads to mixtures of quasi-isoenergetic conformers in solution and makes NOEs very difficult to detect in NMR spectra. In order to improve the quality of the NMR data, Leu-enkephalin was synthesized with 15N-labelled uniformly on all amide nitrogens and examined in a viscous solvent medium at low temperature. HMQC NOESY spectra of the labelled Leu-enkephalin in a DMSOd6/H2O) mixture at 275 K do show numerous NOEs, but these are not consistent with a single conformer and are only sufficient to describe the conformational state as a mixture of several conformers. Here a different approach to the structure-activity relationships of enkephalins is presented: it is possible to analyse the NMR data in terms of limiting canonical structures (i.e. beta- and gamma-turns) and finally to select only those consistent with the requirements of delta selective agonists and antagonists. This strategy results in the prediction of a family of conformers that may be useful in the design of new delta selective opioid peptides.
Istituto Chimica Molecole di Interesse Biologico (associated to the Italian National Institute for the Chemistry of Biological Systems), CNR, Arco Felice, Italy.
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D003080:Cold Temperature; D004743:Enkephalin, Leucine / Q000737:chemistry* / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D009587:Nitrogen Isotopes; D011487:Protein Conformation; D012984:Software; D013329:Structure-Activity Relationship; D014102:Torsion Abnormality
D009587:Nitrogen Isotopes; D004743:Enkephalin, Leucine