Bullfrog Ghrelin Is Modified by n-Octanoic Acid at Its Third Threonine Residue

We have identified the amphibian ghrelin from the stomach of the bullfrog. We also examined growth hormone (GH)-releasing activity of this novel peptide in both the rat and bullfrog. The three forms of ghrelin identified, each comprised of 27 or 28 amino acids, possessed 29% sequence identity to the...

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Bibliographic Details
Published in:The Journal of biological chemistry 2001-11, Vol.276 (44), p.40441-40448
Main Authors: Kaiya, Hiroyuki, Kojima, Masayasu, Hosoda, Hiroshi, Koda, Aya, Yamamoto, Kazutoshi, Kitajima, Yasuo, Matsumoto, Masaru, Minamitake, Yoshiharu, Kikuyama, Sakae, Kangawa, Kenji
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Base Sequence
Caprylates - chemistry
Chromatography, High Pressure Liquid
DNA, Complementary
Freshwater
Ghrelin
Molecular Sequence Data
Peptide Hormones
Peptides - chemistry
Peptides - isolation & purification
Rana catesbeiana
Sequence Homology, Amino Acid
Stomach - chemistry
Threonine - chemistry
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Summary:We have identified the amphibian ghrelin from the stomach of the bullfrog. We also examined growth hormone (GH)-releasing activity of this novel peptide in both the rat and bullfrog. The three forms of ghrelin identified, each comprised of 27 or 28 amino acids, possessed 29% sequence identity to the mammalian ghrelins. A unique threonine at amino acid position 3 (Thr3) in bullfrog ghrelin differs from the serine present in the mammalian ghrelins; this Thr3 is acylated by either n-octanoic or n-decanoic acid. The frog ghrelin-28 has a complete structure of GLT (O-n-octanoyl)FLSPADMQKIAERQSQNKLRHGNM; the structure of frog ghrelin-27 was determined to be GLT(O-n-octanoyl)FLSPADMQKIAERQSQNKLRHGN; frog ghelin-27-C10 possessed a structure of GLT(O-n-decanoyl)FLSPADMQKIAERQSQNKLRHGN. Northern blot analysis demonstrated that ghrelin mRNA is predominantly expressed in the stomach. Low levels of gene expression were observed in the heart, lung, small intestine, gall bladder, pancreas, and testes, as revealed by reverse transcription polymerase chain reaction analysis. Bullfrog ghrelin stimulated the secretion of both GH and prolactin in dispersed bullfrog pituitary cells with potency 2–3 orders of magnitude greater than that of rat ghrelin. Bullfrog ghrelin, however, was only minimally effective in elevating plasma GH levels following intravenous injection into rats. These results indicate that although the regulatory mechanism of ghrelin to induce GH secretion is evolutionary conserved, the structural changes in the different ghrelins result in species-specific receptor binding.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M105212200