Purification of a 41-kDa insulin-like growth factor binding protein from serum of chinook salmon, Oncorhynchus tshawytscha.
In salmon, at least three insulin-like growth factor binding proteins (IGFBPs) with molecular masses of 41, 28, and 22kDa exist in serum. The 41-kDa IGFBP is up-regulated by growth hormone treatment and down-regulated by fasting, suggesting that it is a homolog of IGFBP-3. We purified the 41-kDa IGFBP from chinook salmon serum by IGF-I affinity chromatography followed by reversed-phase high pressure liquid chromatography. Purified IGFBP appeared as doublet bands on electrophoresis and was N-glycosylated. Analysis of partial N-terminal amino acid sequence revealed that salmon 41-kDa IGFBP has the cysteine rich domain conserved among IGFBP family. In a binding assay using 125I-salmon IGF-I, purified 41-kDa IGFBP specifically bound salmon IGF-I, human IGF-I and human IGF-II, but neither Long R(3)IGF-I nor salmon insulin, showing that binding characteristics of the salmon IGFBP are similar to those of mammalian IGFBPs. Although the partial amino acid sequence of 41-kDa IGFBP showed highest homologies with zebrafish and seabream IGFBP-2, the highly conserved nature of the N-terminus makes it impossible to identify the type of IGFBP from partial sequence data. However, based on physiological responses, molecular weight and type of glycosylation, the 41-kDa IGFBP is most similar to mammalian IGFBP-3.
Shimizu
Munetaka
M
Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Boulevard East, Seattle, WA 98112, USA. munetaka@noaa.gov
Swanson
Penny
P
Hara
Akihiko
A
Dickhoff
Walton W
WW
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood* / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012474:Salmon / Q000097:blood*; D017386:Sequence Homology, Amino Acid
D018969:Insulin-Like Growth Factor Binding Proteins