Preferred conformational state of the N-terminus section of a bovine growth hormone fragment (residues 96-133) in water is an omega loop

Conformational analysis of cyclo(2,9)-Ac-QCRSVEGSCG-OH from the C-terminal loop of human growth hormone

A 10 amino acid residue cyclic peptide, cyclo(2,9)-Ac-Gln1-Cys2-Arg3-Ser4-Val5-Glu6-Gly7 -Ser8-Cys9-Gly10, from the C-terminal region of human growth hormone (hGH) was synthesized and studied by 2D proton NMR and molecular dynamics (MD) simulations. The solubility of the peptide was low in water; hence, NMR studies were done in two solvent mixtures, water and deuterated dimethyl sulfoxide. NOE-constrained molecular dynamics and MD simulations resulted in major and minor conformers in solution. The major conformer has a type I beta-turn at Gln1-Cys2-Arg3-Ser4 and a loop structure around Glu6-Gly7-Ser8. Comparison of the conformation of this peptide with the peptide fragment 181-190 in the intact hGH protein X-ray crystal structure indicated that the synthetic peptide retains some structural similarity to the intact protein. Since the C-terminal region is important in binding the hGH protein to its receptor, the conformation of the synthetic peptide could be useful in understanding the binding mechanism.

Antigenic structure of bovine growth hormone: location of a growth enhancing region

Site-directed antisera generated by peptide immunization have been used to study the antigenicity of bovine growth hormone (bGH). Prediction of sequential antigenic sites has been performed using secondary structure information derived from the 'Protean' prediction routine. The structures predicted by this programme agree closely with the corresponding structure of GH recently derived from crystallographic studies. We have previously shown that the binding of monoclonal antibodies of particular epitope specificity to human or bovine GH results in significant enhancement of hormonal activity in vivo; however, the sites recognized by these antibodies were not known. Here we identify a sequence region, corresponding to a loop structure joining helices 3 and 4, which, is associated with the growth enhancement phenomenon. Antisera raised to either of two overlapping peptides (residues 120-140 and 134-154) significantly increase the biological activity of GH in vivo. Antisera directed to other regions on the GH molecule failed to demonstrate this property. Coincidentally, the sites recognized by the growth-enhancing anti-peptide antisera overlap with the site on GH which is highly susceptible to proteolytic cleavage; such cleavage has been shown in some cases to result in hormone enhancement.

Receptor and antibody epitopes in human growth hormone identified by homolog-scanning mutagenesis

A strategy, termed homolog-scanning mutagenesis, was used to identify the epitopes on human growth hormone (hGH) for binding to its cloned liver receptor and eight different monoclonal antibodies (Mab's). Segments of sequences (7 to 30 residues long) that were derived from homologous hormones known not to bind to the hGH receptor or Mab's, were systematically substituted throughout the hGH gene to produce a set of 17 chimeric hormones. Each Mab or receptor was categorized by a particular subset of mutant hormones was categorized by a particular subset of mutant hormones that disrupted binding. Each subset of the disruptive mutations mapped within close proximity on a three-dimensional model of hGH, even though the residues changed within each subset were usually distant in the primary sequence. The mapping analysis correctly predicted those Mab's which could or could not block binding of the receptor to hGH and further suggested (along with other data) that the folding of these chimeric hormones is like that of HGH. By this analysis, three discontinuous polypeptide determinants in hGH--the loop between residues 54 and 74, the central portion of helix 4 to the carboxyl terminus, and to a lesser extent the amino-terminal region of helix 1--modulate binding to the liver receptor. Homolog-scanning mutagenesis should be of general use in identifying sequences that cause functional variation among homologous proteins.