Conformation-activity relationship of neuropeptide S and some structural mutants: helicity affects their interaction with the receptor.

Neuropeptide S (NPS) is the endogenous ligand of the previously orphan G-protein coupled receptor now named NPSR. The NPS-NPSR receptor system regulates important biological functions such as sleep/waking, locomotion, anxiety and food intake. Recently, exhaustive Ala scan and d-amino acid scan studies, together with systematic N- and C-terminal truncation, led to the identification of key residues for biological activity. Because conformational preferences might also play an important role, we undertook a detailed conformational analysis of NPS and several analogues in solution. We show that helicity induced by substitution of three flexible residues in the 5-13 regulatory region abolishes biological activity. A parallel pharmacological and conformational study of single and multiple substitutions of glycines 5, 7, and 9 showed that helicity can be tolerated in the C-terminal part of the peptide but not around Gly7. The identification of hNPSR partial agonists heralds the possibility of designing pure NPS receptor antagonists.