Determination of alpha-subunit contact regions of human follicle-stimulating hormone beta-subunit using synthetic peptides.

Follicle-stimulating hormone (FSH) is a glycoprotein hormone composed of two different subunits designated FSH-alpha and FSH-beta. Using synthetic peptides corresponding to the primary structure of human (h) FSH-beta subunit, we previously identified two regions of the beta-subunit, hFSH-(33-53) and hFSH-(81-95), as receptor binding regions. In this report, we tested the ability of synthetic peptides to interact with hFSH-alpha-subunit. Synthetic peptides corresponding to hFSH-beta-(11-25), (41-55), (51-65), and (101-111) were able to bind specifically radioiodinated hFSH-alpha-subunit, suggesting that they represent regions of interaction with the alpha-subunit. These experimental results were in agreement with the location of alpha-subunit contact regions predicted by sequence analysis. Peptides of hFSH-beta-subunit showing maximum specific binding to the alpha-subunit were those possessing minimum interaction with receptor whereas those not binding to alpha-subunit corresponded to regions shown to interact with receptor (hFSH-beta-(33-53) and hFSH-beta-(81-95]. The hFSH-beta-subunit, therefore, seems to have two discontinuous receptor binding regions flanked by three alpha-subunit contact regions.