Conformation−Activity Relationship of Neuropeptide S and Some Structural Mutants:  Helicity Affects Their Interaction with the Receptor

Abstract

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.

Neurobiology, pharmacology, and medicinal chemistry of neuropeptide S and its receptor

“…NPS conformational investigations performed by NMR experiments indicated that NPS presents a completely disordered conformation in water. 64 However, several NH-NH cross peaks were observed by Bernier et al 57 in the NPS region 5-13; this lead these authors to hypothesize the presence of a nascent helix in this region, which, during the NPSR binding process, may favor the formation of a stable a helix structure.…”

“…In fact, both substitutions generated peptide derivatives that showed only slightly reduced potency compared to NPS. 64 This suggests that an a helix conformation (favored by L-Ala but not by D-Ala) is, at least in this portion of the NPS sequence, not important for NPSR binding. Interestingly, [D-Ala 5 ]NPS behaves as a partial agonist at NPSR with efficacy corresponding to half of that of NPS.…”

“…64 This NPS behavior has been ascribed, at least in part, to the presence in position 5, 7, and 9 of the flexible amino acid residue Gly. In order to force NPS to adopt a stable a helix structure, residues 7, 9, and 13 were replaced with Ala. NMR analyses confirmed that [Ala 7,9,13 ]NPS adopts a very stable helix spanning all the peptide sequence but this peptide was completely inactive at NPSR.…”

“…In order to force NPS to adopt a stable a helix structure, residues 7, 9, and 13 were replaced with Ala. NMR analyses confirmed that [Ala 7,9,13 ]NPS adopts a very stable helix spanning all the peptide sequence but this peptide was completely inactive at NPSR. 64 Single amino acid substitutions indicated that only the replacement of Gly 7 with Ala or Aib (2-amino-2-methylpropionic acid) is able to induce a significant helical structure, whereas [ Different results were obtained with substitution of Gly 5 with L-and D-Ala. In fact, both substitutions generated peptide derivatives that showed only slightly reduced potency compared to NPS.…”

Molecular Modeling Studies on the Human Neuropeptide S Receptor and Its Antagonists

“…On the other hand, a series of structure-activity relationship studies have been carried out for the neuropeptide, and some examples of NPS analogues with partial agonist or even antagonist profiles have been reported recently. [18][19][20][21][22][23] More limited information is available about nonpeptide NPSR antagonists, as only one series of bicyclic piperazine derivatives has been published in this regard. [24][25][26] These molecules (Table 1) present NPSR antagonist potencies with K e values from the low nanomolar range to the micromolar level, with non-identical profiles when tested at NPSR-A and NPSR Ile 107.…”