Structure-activity studies on neuropeptide S -: Identification of the amino acid residues crucial for receptor activation

Neuropeptide S ( NPS) has been recently recognized as the endogenous ligand for the previous orphan G-protein-coupled receptor GPR154, now referred to as the NPS receptor ( NPSR). The NPS-NPSR receptor system regulates important biological functions such as sleeping/wakening, locomotion, anxiety, and food intake. To collect information on the mechanisms of interaction between NPS and its receptor, a classical structure-activity relationship study was performed. Human ( h) NPS derivatives obtained by Ala and D-scan and N- and C-terminal truncation were assessed for their ability to stimulate calcium release in HEK293 cells expressing the human recombinant NPSR. The results of this study indicate that ( i) the effect of hNPS is mimicked by the fragment hNPS( 1 - 10); ( ii) Phe(2), Arg(3), and Asn(4) are crucial for biological activity; ( iii) the sequence Thr(8)-Gly(9)-Met(10) is important for receptor activation, although with non-stringent chemical requirements; and ( iv) the sequence Val(6)-Gly(7) acts as a hinge region between the two above-mentioned domains. However, the stimulatory effect of hNPS given intracerebroventricularly on mouse locomotor activity was not fully mimicked by hNPS-( 1 - 10), suggesting that the C-terminal region of the peptide maintains importance for in vivo activity. In conclusion, this study identified the amino acid residues of this peptide most important for receptor activation.