Purification and characterization of rat des-Gln14-Ghrelin, a second endogenous ligand for the growth hormone secretagogue receptor

Ghrelin, a peptide purified from the stomach, is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) and potently stimulates growth hormone release from the pituitary. Ghrelin is modified with an n-octanoyl group at Ser(3). This modification is essential for the activity of ghrelin. Previously, it was not known whether other ligands for GHS-R existed. Here, we report the purification of the second endogenous ligand for GHS-R from rat stomach. This ligand, named des-Gln(14)-ghrelin, is a 27-amino acid peptide, whose sequence is identical to ghrelin except for one glutamine. Southern blotting analysis under low hybridization conditions indicates that no homologue for ghrelin exists in rat genomic DNA. Furthermore, genomic sequencing and cDNA analysis indicate that des-Gln(14)-ghrelin is not encoded by a gene distinct from ghrelin but is encoded by an mRNA created by alternative splicing of the ghrelin gene. This is the first example of a novel mechanism that produces peptide multiplicity. Des-Gln(14)-ghrelin has an n-octanoyl modification at Ser(3) like ghrelin, which is also essential for its activity. Des-Gln(14)-ghrelin-stimulated growth hormone releases when injected into rats. Thus, growth hormone release is regulated by two gastric Peptides, ghrelin and des-Gln(14)-ghrelin.