RECOGNITION OF FOLLICLE-STIMULATING-HORMONE (ALPHA-SUBUNIT) BY A RECOMBINANT RECEPTOR PROTEIN DOMAIN CODED BY AN ALTERNATELY SPLICED MESSENGER-RNA AND EXPRESSED IN ESCHERICHIA-COLI

To assess the functional significance of putative proteins encoded by alternately spliced mRNA of the sheep testicular FSH receptor, a short form cDNA comprising of the first four exons (117 residues mature pro tein) was engineered for expression in Escherichia coli. The expressed protein of molecular mass 15 kDa was purified to homogeneity and veri fied by reaction with an antibody against a synthetic peptide sequence unique to the amino (N)-terminal region FSH receptor. The purified FS H receptor domain protein bound I-125-labeled hFSH in a ligand blot on polyvinylidene difluoride membranes. Further analyses by slot blot re vealed high affinity of the immobilized protein with significant react ion at 10 pmol. As the immobilized receptor protein also reacted with structurally related hormones (I-125-labeled LH/ I-125-labeled human c horionic gonadotropin), we confirmed that-interaction most probably oc curred via the common alpha-subunit of these glycoprotein hormones. Ou r results reveal that this N-terminal portion of the FSH receptor cont ain(s) major site(s) for hormone recognition that could be mediated vi a the alpha-subunit. A rabbit antibody to the receptor inhibited FSH a ction in receptor bearing cells, revealing the utility of such recombi nant FSH receptor protein(s) for modulation of hormone action.