The cDNA-deduced primary structure of human sex hormone-binding globulin and location of its steroid-binding domain |
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Authors: | G L Hammond D A Underhill C L Smith I S Goping M J Harley N A Musto C Y Cheng C W Bardin |
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Institution: | 1. Department of Obstetrics and Gynecology, University of Western Ontario, 375 South Street, London, Ontario N6A 4G5, Canada;2. The Population Council, 1230 York Avenue, New York, NY 10021, USA |
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Abstract: | We have sequenced a cDNA for sex hormone-binding globulin (SHBG) isolated from a phage lambda gt11 human liver cDNA library. The library was screened with a radiolabeled rat androgen-binding protein (ABP) cDNA, and the abundance of SHBG cDNAs was 1 in 750,000 plaques examined. The largest human SHBG cDNA (1194 base-pairs) contained a reading frame for 381 amino acids. This comprised 8 amino acids of a signal peptide followed by 373 residues starting with the known NH2-terminal sequence of human SHBG, and ending with a termination codon. The predicted polypeptide Mr of SHBG is 40,509, and sites of attachment of one O-linked (residue 7) and two N-linked oligosaccharide (residues 351 and 367) chains were identified. Purified SHBG was photoaffinity-labeled with delta 6-3H]testosterone and cleaved with trypsin. The labeled tryptic fragment was isolated by reverse-phase HPLC, and its NH2-terminal sequence was determined. The results suggest that a portion of the steroid-binding domain of SHBG is located between residue 296 and the 35 predominantly hydrophilic residues at the C-terminus of the protein. |
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