IDENTIFICATION OF AMINO-ACID-RESIDUES 300-315 OF THE RAT FSH RECEPTORAS A HORMONE-BINDING DOMAIN - EVIDENCE FOR ITS INTERACTION WITH SPECIFIC REGIONS OF FSH-BETA-SUBUNIT

We previously reported that residues 9-30 of the extracellular N-termi nus domain of the rat FSH receptor, which has no homologous sequence i n receptors for related pituitary glycoprotein hormones, represented a specific FSH binding domain. Further examination of its deduced prima ry structure identified another region, residues 300-315, which was al so unique to the FSH receptor. To determine whether this region of the FSH receptor was involved in hormone binding, a synthetic peptide cor responding to residues 300-315 was studied with respect to its ability to bind FSH, as well as a series of nine overlapping synthetic peptid es corresponding to the entire primary structure of the hormone specif ic FSH beta-subunit. I-125-FSH rec-(300-315) peptide bound to immobili zed human, ovine and bovine FSH, but not to prolactin or ovalbumin. Of the nine synthetic peptides studied, binding was restricted to FSH be ta residues 21-35, and to a much lesser extent (20%) to residues 11-25 . All binding was abolished in the presence of excess solubilized FSH receptor. Earlier studies indicated that although FSH binds to FSH rec (9-30) peptide, residues 11-25 or 21-35 of the FSH beta-subunit were n ot involved. Our results suggest the FSH receptor N-terminus, extracel lular residues 300-315, may define a FSH binding site, and that bindin g of FSH beta-subunit may occur via interactions with FSH beta 21-35 a nd 11-25. (C) 1995 Academic Press, Inc.