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The NMR‐derived conformation of neuropeptide AF, an orphan G‐protein coupled receptor peptide

The tertiary structure of the pain modulating and anti‐opiate neuropeptide, human neuropeptide AF (NPAF) (the sequence is AGEGLNSQFWSLAAPQRF–NH2), was determined by 1H‐NMR. The structure of NPAF was determined in two solvent systems, namely 50%/50% trifluoroethanol‐d3/H2O (TFE/H2O) and in the cell membrane mimetic micelle, sodium dodecylsulfate‐d25 (SDS). The receptor for NPAF is an orphan G‐protein coupled receptor, and the micellar SDS solvent system was used to emulate the cell membrane surface in line with the Cell Membrane Compartments Theory proposed by R. Schwyzer (Biopolymers, 1995, Vol. 37, pp. 5–16). In both solvent systems, NPAF was found to be primarily α‐helical within the central portion of the molecule, from Asn6 to Ala14. The N‐terminus was random in both solvent systems. In the SDS solution, the C‐terminal tetrapeptide was structured and formed a type I β‐turn, whereas in TFE/H2O it was unstructured, showing the importance of the C‐terminal tetrapeptide in receptor recognition. NPAF was found to associate with SDS, and was shown to be near the surface of the micelle by spin label studies with 5‐doxyl‐stearic acid. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 201–215, 2003