Structure/function analyses of human sex hormone-binding globulin by site-directed mutagenesis.
Human sex hormone-binding globulin (hSHBG) and rat androgen-binding protein (rABP) exhibit distinct affinities for sex-steroids. We therefore constructed and expressed a hSHBG/rABP hybrid cDNA encoding the N-terminal portion of hSHBG (205 residues) and the C-terminal portion of rABP (168 residues). The resulting chimera displayed similar steroid-binding characteristics as hSHBG and was recognised by a monoclonal antibody (S1B5) for hSHBG. We then created substitutions at Ser-133, His-136 and Met-139. The Asp-133 and Gln-136 mutants bound steroids in the same way as normal hSHBG while the steroid-binding affinity of Trp-139 was reduced. All three mutants cross-reacted similarly in a hSHBG radioimmunoassay, but Gln-136 was recognised poorly by the S1B5 antibody. These data imply that residues involved in steroid-binding are located within the N-terminal half of hSHBG and include Met-139, and that the S1B5 epitope is located in this region.
Bocchinfuso
W P
WP
Department of Obstetrics and Gynecology, University of Western Ontario, London, Canada.
Warmels-Rodenhiser
S
S
Hammond
G L
GL
D000595:Amino Acid Sequence; D000727:Androgen-Binding Protein / Q000235:genetics; D000818:Animals; D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D013196:Dihydrotestosterone / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012738:Sex Hormone-Binding Globulin / Q000235:genetics* / Q000378:metabolism; D013329:Structure-Activity Relationship
D000727:Androgen-Binding Protein; D000911:Antibodies, Monoclonal; D011993:Recombinant Fusion Proteins; D012738:Sex Hormone-Binding Globulin; D013196:Dihydrotestosterone