MAMMALIAN EXPRESSION OF THE HUMAN SEX STEROID-BINDING PROTEIN OF PLASMA (SBP OR SHBG) AND TESTIS (ABP) - CHARACTERIZATION OF THE RECOMBINANT PROTEIN

A full-length 1,209 bp cDNA encoding the human sex steroid-binding protein of plasma (SBP or SHBG) and testis (ABP) was constructed and expressed in BHK-21 cells. The sequence agrees with the published gene and protein sequences. The cells were found to secrete SBP following transfection and G418r selection. The recombinant protein binds 5-alpha-dihydrotestosterone with a K(d) of 0.28 nM. It also binds testosterone and 17-beta-estradiol but not progesterone, estrone or cortisol revealing a steroid-binding specificity identical to that of human SBP. SDS-PAGE patterns are less complex than human SBP and show a monomeric molecular weight of about 43 kDa.