Structural Divergence of Human Ghrelin

Hiroshi Hosoda, Masayasu Kojima, Tsunekazu Mizushima, Shigeomi Shimizu, Kenji Kangawa
2002 Journal of Biological Chemistry  
Ghrelin, a novel 28-amino acid peptide with an n-octanoyl modification at Ser 3 , was isolated from rat stomach and found to be an endogenous ligand for the growthhormone secretagogue receptor (GHS-R). This octanoyl modification is essential for ghrelin-induced GH release. We report here the purification and identification of human ghrelin from the stomach, as well as structural analysis of the human ghrelin gene and quantitation of changes in plasma ghrelin concentration before and after
more » ... ctomy. Human ghrelin was purified from the stomach by gel filtration and high performance liquid chromatography, using a ghrelin-specific radioimmunoassay and an intracellular calcium influx assay on a stable cell line expressing GHS-R to test the fractions. In the course of purification, we isolated human ghrelin of the expected size, as well as several other ghrelin-derived molecules. Classified into four groups by the type of acylation observed at Ser 3 ; these peptides were found to be non-acylated, octanoylated (C8:0), decanoylated (C10:0), and possibly decenoylated (C10:1). All peptides found were either 27 or 28 amino acids in length, the former lacking the C-terminal Arg 28 , and are derived from the same ghrelin precursor through two alternative pathways. The major active form of human ghrelin is a 28-amino acid peptide octanoylated at Ser 3 , as was found for rat ghrelin. Synthetic octanoylated and decanoylated ghrelins produce intracellular calcium increases in GHS-R-expressing cells and stimulate GH release in rats to a similar degree. Both ghrelin and the ghrelin-derived molecules were found to be present in plasma as well as stomach tissue. Plasma levels of immunoreactive ghrelin after total gastrectomy in three patients were reduced to approximately half of their pre-gastrectomy values, after which they gradually increased. This suggests that the stomach is the major source of circulating ghrelin and that other tissues compensate for the loss of ghrelin production after gastrectomy.
doi:10.1074/jbc.m205366200 pmid:12414809 fatcat:yxmvbepnzbgixh43j2kxavsepi