Endocrine Abstracts

Ghrelin, the endogenous ligand for the GH secretagogue receptor type 1a (GHS-R1a), is a peptide with a post-translational octanoyl modification on Ser-3. Previous studies of ghrelin derivatives showed that the pendant group at Ser-3 plays an essential role in the bioactivity. The acylated peptide specifically releases growth hormone (GH) both in vivo and in vitro, while the desoctanoyl form of the hormone is at least 100-fold less potent than the parent peptide.

Binding events of ligands to receptors are the key for understanding the biological processes. Gaining insight into protein-protein and protein-ligand interactions in solution has recently become possible on an atomic level by new NMR spectroscopic techniques.

In this work, the mapping of the interaction of ghrelin with its receptor by NMR techniques in living cells is presented. The evaluation between spectra with stably transfected and wild type cells of the same cell line, allowed a mapping of the interactions of ghrelin and desacyl-ghrelin with the target GHS-R1a receptor. Ghrelin was found to have a higher number of residues affected by chemical shift perturbation (CSP) or slow conformational exchange (SCE) effects by interaction with the receptor, and the n-octanoic group was seen to be clearly necessary for the interaction with the receptor, supporting the conclusion that the NMR data in living cells report accurately the functional interaction of these peptides. The large number of SCE effects detected for ghrelin: Ser3, Phe4, Leu5, Val12, Gln13/Gln14, Lys16/Lys19, Glu17 and Lys24, suggest that the binding to its receptor is accompanied of a large conformational change respect to the random coil structure described in free solution.