Identification of Amino Acid Residues 300-315 of the Rat FSH Receptor as a Hormone Binding Domain: Evidence for Its Interaction with Specific Regions of FSHβ-Subunit

Abstract We previously reported that residues 9-30 of the extracellular N-terminus domain of the rat FSH receptor, which has no homologous sequence in receptors for related pituitary glycoprotein hormones, represented a specific FSH binding domain. Further examination of its deduced primary structure identified another region, residues 300-315, which was also unique to the FSH receptor. To determine whether this region of the FSH receptor was involved in hormone binding, a synthetic peptide corresponding to residues 300-315 was studied with respect to its ability to bind FSH, as well as a series of nine overlapping synthetic peptides corresponding to the entire primary structure of the hormone specific FSHβ-subunit. 125 I-FSH rec-(300-315) peptide bound to immobilized human, ovine and bovine FSH, but not to prolactin or ovalbumin. Of the nine synthetic peptides studied, binding was restricted to FSHβ 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 FSHβ-subunit were not involved. Our results suggest the FSH receptor N-terminus, extracellular residues 300-315, may define a FSH binding site, and that binding of FSHβ-subunit may occur via interactions with FSHβ 21-35 and 11-25.