CONFORMATIONAL PREFERENCES OF LEU-ENKEPHALIN IN REVERSE MICELLES AS MEMBRANE-MIMICKING ENVIRONMENT

Enkephalin represents one of the bioactive peptide molecules most exte nsively investigated both in solution and in the crystal stare. Depend ing upon the environment chosen. for such studies, three main conforma tional states were identified for this flexible, linear pentapeptide-i .e., an extended conformation, a single-bend, and a double-bend struct ure. Since CD and Fourier transform ir (FTIR) spectra of Leu-enkephali n solubilized in negatively charged reverse micelles of bis(2-ethylhex yl) sulfosuccinate sodium salt/isooctane/water were supportive of a re stricted conformational space of the aromatic side chains and of a ben ded type fold, we have analyzed by nmr the conformational preferences of Leu-enkephalin in reverse micelles using a synthetic [C-13, N-15]-b ackbone-labeled sample. The overall conformation derived front nuclear Overhauser effect spectroscopy (NOESY) and N-15-filtered relating fra me NOESY (ROESY) spectra and by distance geometry calculations is a do uble-bend fold of the backbone that is comparable to one of the known x-ray structures. Thereby the tyrosine side chain is inserted into the hydrophobic core of the reverse micelles in a restrained conformation al space as well evidenced by NOEs between the aromatic ring protons a nd the surfactant. The proximity of the aromatic rings of tyrosine and phenylalanine indicate a preferred structure consistent with the post ulated conformation of the opioid peptide in the S-receptor-bound star e. These results confirm the interesting and promising properties of r everse micelles as membrane mimetica. (C) 1997 John Wiley & Sons, Inc.