The glycoprotein hormones: Recent studies of structure-function relationships

The structural features of the heterodimeric glycoprotein hormones (LH, FSH, TSH, and hCG) are briefly reviewed. Removal of carbohydrate chains does not reduce binding of the hormones to membrane receptors, but markedly reduces biological responses. The glycopeptides from the hormone do not reduce binding of native hormone to receptors but do reduce biological responses. Newer data concerned with replication of different regions of the peptide chains of these molecules using synthetic peptides are reviewed and presented. These studies indicate that two regions on the common α subunit are involved with receptor binding of the LH, hCG, and TSH molecules. These regions are α26 to 46 and α75-92. Two synthetic disulfide loop peptides from the hCGβ subunit β38-57 and β93-100 also block binding of hCG to its receptor. In addition, the β38-57 peptide stimulates testosterone production by Leydig cells. These data indicate that glycoprotein hormone binding to plasma membrane receptors involves a discontinuous site on the hormone that spans both the α and β subunits, and that the α subunit sites are similar for several hormones.