PT  - JOURNAL ARTICLE
AU  - Birgitte Holst
AU  - Manja Lang
AU  - Erik Brandt
AU  - Anders Bach
AU  - Andrew Howard
AU  - Thomas M. Frimurer
AU  - Annette Beck-Sickinger
AU  - Thue W. Schwartz
TI  - Ghrelin Receptor Inverse Agonists: Identification of an Active Peptide Core and Its Interaction Epitopes on the Receptor
AID  - 10.1124/mol.106.024422
DP  - 2006 Sep 01
TA  - Molecular Pharmacology
PG  - 936--946
VI  - 70
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/70/3/936.short
4100  - http://molpharm.aspetjournals.org/content/70/3/936.full
SO  - Mol Pharmacol2006 Sep 01; 70
AB  - [d-Arg1,d-Phe5,d-Trp7,9,Leu11]Substance P functions as a low-potency antagonist but a high-potency full inverse agonist on the ghrelin receptor. Through a systematic deletion and substitution analysis of this peptide, the C-terminal carboxyamidated pentapeptide wFwLX was identified as the core structure, which itself displayed relatively low inverse agonist potency. Mutational analysis at 17 selected positions in the main ligand-binding crevice of the ghrelin receptor demonstrated that ghrelin apparently interacts only with residues in the middle part of the pocket [i.e., between transmembrane (TM)-III, TM-VI and TM-VII]. In contrast, the inverse agonist peptides bind in a pocket that extends all the way from the extracellular end of TM-II (AspII:20) across between TM-III and TM-VI/VII to TM-V and TM-IV. The potency of the main inverse agonist could be improved up to 20-fold by a number of space-generating mutants located relatively deep in the binding pocket at key positions in TM-III, TM-IV and TM-V. It is proposed that the inverse agonists prevent the spontaneous receptor activation by inserting relatively deeply across the main ligand-binding pocket and sterically blocking the movement of TM-VI and TM-VII into their inward-bend, active conformation. The combined structure-functional analysis of both the ligand and the receptor allowed for the design of a novel, N-terminally Lys-extended analog of wFwLL, which rescued the high-potency, selective inverse agonism that was dependent upon both AspII:20 and GluIII:09. The identified pharmacophore can possibly serve as the basis for targeted discovery of also nonpeptide inverse agonists for the ghrelin receptor. The American Society for Pharmacology and Experimental Therapeutics