Delineation and synthesis of the membrane receptor-binding domain of sex hormone-binding globulin.

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein which binds certain steroids. It, in turn, binds to a specific receptor on cell membranes. This work was undertaken to identify, isolate, sequence, and synthesize the region of SHBG that interacts with its membrane receptor. To accomplish this, highly purified human SHBG was digested with trypsin. The SHBG-derived tryptic peptides were separated by high performance liquid chromatography. They were evaluated for their ability to compete with 125I-SHBG for binding to the SHBG receptor solubilized from human prostatic membranes. Only a single peptide, corresponding to residues 48-57 of the known sequence of human SHBG, inhibited receptor binding. A synthetic decapeptide with this amino acid sequence also competitively inhibited SHBG binding.