Identification of a ghrelin-like peptide in two species of shark, Sphyrna lewini and Carcharhinus melanopterus.
In this study, we identified a ghrelin-like peptide (ghrelin-LP) in two elasmobranchs. The peptide, isoforms and cDNA encoding its precursor were isolated from the stomach of two sharks, the hammerhead (HH) shark (Sphyrna lewini) and the black-tip reef (BTR) shark (Carcharhinus melanopterus). The ghrelin-LP isolated from each shark was found to be 25 amino acids in length and exhibit high sequence homology with each other; only three amino acids were different. As has been shown in tetrapod and teleost fish ghrelins, shark ghrelin-LPs possess two forms that are distinguished by having the third serine residue (Ser) acylated by either octanoic or decanoic acid. The N-terminal four residues (GVSF), known as the active core of ghrelin, are not identical to those of other species (GSSF). Nevertheless, shark ghrelin-LP elevated Ca(2+) levels in CHO cell line expressing the growth hormone secretagogue receptor (GHS-R). Unlike teleosts ghrelin's, shark ghrelin-LPs are not amidated at the C-terminus. Messenger RNA of ghrelin-LP in the HH shark was predominantly expressed in the stomach as seen in other species, followed by the brain, intestine, gill, heart and liver. The nucleotide sequence of the ghrelin-LP gene in the HH shark was characterized to compare organization of the ghrelin gene with those in other species. The size of the HH ghrelin-LP gene was 8541 bp, two to ten times larger than that of other species studied to date. The HH ghrelin-LP gene is composed of five exons and four introns, which is the same as ghrelin genes in mammals, chicken and rainbow trout. In conclusion, the shark ghrelin-LPs identified in this study exhibit many characteristics for ghrelin in terms of peptide modifications, GHS-R activation, tissue distribution, and gene organization; however, it is necessary to further clarify their biological properties such as growth hormone-releasing or orexigenic activity before designating these peptides as ghrelin.
Kawakoshi
Akatsuki
A
Department of Biochemistry, National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka 565-8565, Japan. kawakosi@ri.ncvc.go.jp <kawakosi@ri.ncvc.go.jp>
Kaiya
Hiroyuki
H
Riley
Larry G
LG
Hirano
Tetsuya
T
Grau
E Gordon
EG
Miyazato
Mikiya
M
Hosoda
Hiroshi
H
Kangawa
Kenji
K
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002874:Chromosome Mapping; D006224:Cricetinae; D003412:Cricetulus; D054439:Ghrelin; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D036361:Peptide Hormones / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D017386:Sequence Homology, Amino Acid; D012754:Sharks / Q000378:metabolism*; D013270:Stomach / Q000737:chemistry; D014018:Tissue Distribution
D054439:Ghrelin; D010446:Peptide Fragments; D036361:Peptide Hormones; D020033:Protein Isoforms