AN IMMOBILIZED PEPTIDE ARRAY IDENTIFIES ANTIBODIES TO A DISCONTINUOUSEPITOPE IN THE EXTRACELLULAR DOMAIN OF THE BOVINE GROWTH-HORMONE RECEPTOR

Using an array of overlapping decapeptides representing the extracellu lar domain of the bovine (b) growth-hormone receptor (GHR) we have map ped the continuous, dominant epitopes defined by five rabbit and one g uinea pig polyclonal antisera to recombinant bovine growth-hormone-bin ding protein (rbGHBP). We report that six major epitopes are identifie d by these antisera and that these largely occur in areas of non-order ed secondary structure, although there is some contribution from the e xtensive beta-sheet structure of GHBP. Similar to our previously descr ibed studies for growth hormone (GH), we have again found slight diffe rences between animals in the tract location of these epitopes. Using peptide-affinity chromatography we have isolated a population of antib odies reactive with epitope 1 (the N-terminal epitope:GHBP residues 21 -38). Analysis of these antibodies by further peptide affinity chromat ography and competitive radioimmunoassay experiments indicated cross-r eactivity of epitope-1-specific antibodies with epitope 4 (in the inte rdomain hinge region of the GHBP:residues 111-126). We suggest that, a lthough separate in the primary structure of the molecule, the tertiar y fold exhibited by GHBP may bring into close proximity areas of seque nce representing epitope 1 and epitope 4 such that they represent a co nformational epitope. Under these conditions our experiments indicate that peptides 1 and 4 may represent partial functional epitopes for th is antibody population and consequently demonstrate that this approach may be useful in describing discontinuous epitopes.