Identification of a follicle-stimulating hormone receptor-binding region in hFSH-beta-(81-95) using synthetic peptides.

Pituitary and placental glycoprotein hormones are heterodimers with alpha-subunits of identical primary structure, but dissimilar beta-subunits. Regions of structural similarity between the beta-subunits might be involved in interaction with the homologous alpha-subunits, and regions of structural dissimilarity could, therefore, be candidates for receptor interactions. A restrained matrix dot-plot analysis identified hFSH-beta-(8-32) and hFSH-beta-(55-65) as candidates for interaction with alpha-subunit. Therefore, by subtraction, hFSH-beta-(33-54) and hFSH-beta-(66-111) seemed candidates for regions of interaction with receptor. In a previous report we demonstrated that hFSH-beta-(33-53) represented a receptor-binding region of hFSH-beta. Analysis of structural parameters (flexibility, surface probability, secondary structure prediction, etc.) indicates similarities between hFSH-beta-(33-53) and hFSH-beta-(85-95), suggesting the latter might be the component of hFSH-beta-(61-111) interacting with the receptor. Testing of 11 synthetic peptides, corresponding to the primary structure of hFSH-beta, demonstrated that hFSH-beta-(31-45)-peptide amide, were unique in ability to inhibit 125I-follicle-stimulating hormone binding to receptor. hFSH-beta-(81-95)-peptide amide also stimulated estradiol biosynthesis in Sertoli cell cultures. The correlation between binding inhibition and surface probability, flexibility, and predicted secondary structure (alpha, extended, and turn) was highly significant (R2 = 0.87, p less than 0.0001). Regression significance for these parameters, taken individually, were very poor. Receptor-binding regions, therefore, appear to be characterized by a particular and complex arrangement of secondary structure motifs, surface probability, and flexibility.