Pain peptides. Solution structure of orphanin FQ2

Orphanin FQ2 (OFQ2) is a novel heptadecapeptide generated from prepronociceptin (PPNOC), the same precursor of nociceptin/orphanin FQ and nocistatin. OFQ2 is a potent analgesic when administered both supraspinally and spinally. In order to clarify the structural relationship with all peptides generated from PPNOC, we have undertaken the conformational study of OFQ2 in water and in structure-promoting solvent media. Nuclear magnetic resonance data and theoretical calculations are consistent with a well defined helical structure from Met(5) to Ser(16). The uniform distribution of hydrophobic residues along the helix suggests that OFQ2 may interact with the transmembrane helices of a receptor akin to those of nociceptin and opioids.