IN-VITRO INHIBITION OF THE BIOACTIVITY OF FOLLICLE-STIMULATING-HORMONE BY ANTISERA AGAINST A PEPTIDE REPRESENTING PART OF THE FSH-RECEPTOR

The aim of the present work was to define an FSH receptor (FSHR) pepti de that can induce antibodies that will inhibit the bioactivity of FSH . Therefore, the hFSHR sequence was aligned with that of all other kno wn G-protein coupled receptors. An area with increased sequence homolo gy was identified between the FSH-, LH-, TSH receptors, the C5a recept or and the IL8 receptor. The similarity consists of a richness in acid ic (D and E) and hydrophobic (Y and F) residues. In hFSHR the sequence is EDNESSYSRGFDMTYTEFDYDLCNEVVD (amino acid 299-326). Research on bot h the C5a- and IL8-receptor has indicated that this part is responsibl e for hormone binding but not for signal transduction. Protamine, an a ntagonist for both the C5a- and IL8 receptor also inhibited the bioact ivities of FSH and LH when tested in a bioassay. This suggests that in the hFSHR this region might also be involved in hormone binding. Spec ificity of this region towards the diverse ligands all binding to the C5a or to the IL8 receptor might be attributed to differences in the p rofile of alternating basic and hydrophobic residues. Therefore, the h ypothesis was tested as to whether antisera raised against peptides of this FSHR-domain would inhibit FSH-bioactivity but not LH-bioactivity . Indeed antisera were found (anti-hFSHR 309-322) that inhibited the b iological activity of FSH in a bioassay. These antisera proved to be s pecific since they did not inhibit the bioactivity of LH. These data s uggest that the core sequence (hFSHR 309-322) of the aligned domain of the hFSHR, in analogy to the IL8- and C5a receptors, is involved in h ormone binding and ligand specificity. This domain therefore forms a v aluable tool in FSH- and FSHR research for scientific and medical purp oses. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.