D-AMINO-ACID SUBSTITUTION OF RESIDUE-32 TO RESIDUE-46 OF THE GLYCOPROTEIN HORMONE COMMON ALPHA-SUBUNIT - DEVELOPMENT OF A SYNTHETIC GLYCOPROTEIN HORMONE ANTAGONIST

We have used single- or double-point D-amino acid substitutions to stu dy the structure-function relationships involving residues 32 to 46 of the glycoprotein hormone common alpha-subunit (GPHa) and the testicul ar follicle-stimulating hormone (FSH) and luteinizing hormone (LH/hCG) receptors. D-Amino acid substitution analogs of GPHa(32-46) were synt hesized and tested in both FSH and hCG radioligand receptor assays usi ng bovine calf testis membranes as receptor source. Correct orientatio n of the amino acid side chains was generally of paramount importance for peptide interaction with receptor and bioactivity. Most substituti ons with corresponding D-amino acids did not enhance the potency of na tive GPHa(32-46). A significant increment in peptide potency, however, was observed by inversion of configuration at positions Ser-34 and Th r-39 with D-amino acid isoforms. Based on the relative potency of each peptide analog, [D-Ser-34, D-Thr-39]GPHa(32-46) was approximately two fold more potent than native peptide GPHa(32-46) in both FSH and hCG r adioligand receptor assays. [D-Ser-34, D-Thr-39]GPHa(32-46) also marke dly inhibited FSH-stimulated estradiol biosynthesis in cultured rat Se rtoli cells. The present study is unique in that it represents the fir st report of utilizing D-amino acid substitution to develop more poten t peptide analogs related to the glycoprotein hormone common alpha-sub unit region 32-46. Our results offer hope for the development of more potent and stabile peptide antagonists of possible usefulness in ferti lity regulation and control.