title: Characterization and measurement of the plasma alpha- and beta-sex hormone-binding globulin paralogs in salmon.
abstract: When the biochemical characteristics of coho salmon SHBG (csSHBG) plasma were examined, two different steroid-binding profiles were obtained corresponding to recombinant csSHBG-alpha and csSHBG-beta. These SHBG paralogs share only 24% sequence identity, and this explains their unique steroid-binding properties. Both proteins bind testosterone, but csSHBG-alpha also binds androstenedione (Kd = 2.8 nm) and ethinylestradiol with high affinity, whereas csSHBG-beta binds estradiol (Kd = 0.8 nm) preferentially. When analyzed by gel filtration, csSHBG-alpha displays the properties of a 153-kDa homodimer, whereas csSHBG-beta elutes as a 68-kDa monomer. The unique steroid-binding properties of csSHBG-alpha and csSHBG-beta allowed us to develop an assay for their measurements in immature (pre-smolt) and mature coho salmon blood. Plasma csSHBG-alpha levels were 3- to 4-fold higher than those of csSHBG-beta irrespective of developmental stage or sex and correlate with each other. The major site of csSHBG-alpha expression in pre-smolts and mature fish is the liver, but low levels of csSHBG-alpha mRNA are present in stomach/intestine of mature fish. In pre-smolts, high levels of csSHBG-beta mRNA are present in gills and ovary, whereas csSHBG-beta mRNA is most abundant in muscle and stomach/intestine of mature fish. Based on the differences in csSHBG-alpha and csSHBG-beta plasma levels and their tissue expression profiles, we conclude that gills and/or muscle contribute mainly to plasma SHBG-beta in coho salmon. The assays we have developed will enable studies of how SHBG-alpha/SHBG-beta biosynthesis is regulated throughout the salmonid life cycle and how they influence steroid hormone action in these fish.
authors.affiliation: Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, British Columbia, Canada V5Z 4H4.
authors.forename: Solange
authors.initials: S
authors.lastname: Miguel-Queralt
authors.forename: Caroline
authors.initials: C
authors.lastname: Underhill
authors.forename: Robert H
authors.initials: RH
authors.lastname: Devlin
authors.forename: Geoffrey L
authors.initials: GL
authors.lastname: Hammond
mesh_terms: D000595:Amino Acid Sequence; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D003001:Cloning, Molecular; D004958:Estradiol / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008099:Liver / Q000502:physiology; D008297:Male; D008969:Molecular Sequence Data; D017684:Oncorhynchus kisutch / Q000097:blood* / Q000235:genetics; D017686:Oncorhynchus mykiss / Q000235:genetics; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012727:Sex Characteristics; D012738:Sex Hormone-Binding Globulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D012738:Sex Hormone-Binding Globulin; D000735:Androstenedione; D004958:Estradiol; D012313:RNA