There are three distinct forms of bombesin. Identification of [Leu13]bombesin, [Phe13]bombesin, and [Ser3,Arg10,Phe13]bombesin in the frog Bombina orientalis.
Amphibian bombesin is the prototypic peptide that defines the bombesin-like peptide family. In this paper we show that in the frog Bombina orientalis, there are actually 3 distinct forms of bombesin, and each of these peptides is an agonist with differing affinities for the known bombesin receptors. Oligonucleotides complementary to the 5'- and 3'-untranslated regions of the bombesin mRNA were used to amplify bombesin-related cDNAs from the skin, brain, and gut of B. orientalis. Three classes of cDNAs were found. One class encoded the previously characterized form of bombesin which has a Leu at position 13 ([Leu13]bombesin). The other two classes, respectively, encoded new bombesin-like peptides which we have designated as [Phe13]bombesin and [Ser3,Arg10,Phe13]bombesin ([SAP]bombesin). The existence of [SAP]bombesin in skin was confirmed by tandem mass spectrometry. Polymerase chain reaction analysis of genomic DNA showed the mRNAs for [Leu13]bombesin, [Phe13]bombesin, and [SAP]bombesin most likely arise from separate genes. Polymerase chain reaction analysis showed different patterns of tissue-specific expression for each form. [Leu13]Bombesin and [SAP]bombesin were predominantly expressed in skin, brain, and gut; [Phe13]bombesin was expressed only in brain, and [Leu13]bombesin predominated in oocytes. [SAP]Bombesin contained a cleavage site between residues 4 and 5, which if used would yield the peptide [SAP]bombesin(5-14) which has the sequence [Gln3,Arg6]neuromedin B. Thus a frog homolog of NMB could derive from the [SAP]bombesin prohormone. [Phe13]Bombesin, [SAP]bombesin, and [SAP]bombesin(5-14) were synthesized and their affinities for the mammalian bombesin-like peptide (GRP and NMB) receptors determined. These peptides acted as agonists for the GRP and NMB receptors, with relative potencies for the GRP receptor of [Leu13]bombesin > [Phe13]bombesin > [SAP]bombesin(5-14) > [SAP]bombesin and for the NMB receptor of [Phe13]bombesin > [SAP]bombesin(5-14) > [Leu13]bombesin > [SAP]bombesin. None of these peptides demonstrated high affinity binding for the BRS-3 receptor. The different receptor affinities and tissue distribution of these peptides suggests distinct physiologic roles and raises the possibility of as yet uncharacterized mammalian homologs of these new amphibian peptides.
Nagalla
S R
SR
Division of Neuroscience, Oregon Regional Primate Center, Beaverton, 97006, USA.
Barry
B J
BJ
Falick
A M
AM
Gibson
B W
BW
Taylor
J E
JE
Dong
J Z
JZ
Spindel
E R
ER
D000595:Amino Acid Sequence; D000818:Animals; D001001:Anura; D001483:Base Sequence; D001667:Binding, Competitive; D001839:Bombesin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D009865:Oocytes / Q000502:physiology; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D018004:Receptors, Bombesin / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000737:chemistry / Q000378:metabolism*; D014981:Xenopus
D012333:RNA, Messenger; D018004:Receptors, Bombesin; D011994:Recombinant Proteins; D001839:Bombesin