title: Effect of salts on the structure of a potent analog of growth hormone releasing hormone as determined by optical spectroscopy.
abstract: Optical spectroscopic methods (circular dichroism, analytical ultracentrifugation, and static light scattering) were employed to study the solution behavior of an N-terminal-acylated 76-residue analog of growth hormone releasing hormone (GHRH). The GHRH analog had a 30% helical configuration in aqueous acidic solution, unlike other GHRH analogs that had a random coil configuration in aqueous solutions, and self-associated. High concentrations (7 M) of urea were required to obtain monomeric peptide, but such urea concentrations unfolded the peptide. Therefore, the folding and self-association were related events. The self-association and helix content were increased by the addition of various cations (e.g., Na+, Ca2+). In 7 M urea, when these cations were added, the peptide started to refold toward its aqueous conformation in a pH dependent manner; at low pH (2.5-3.5) the peptide folded to approximately 50% of the native configuration. At neutral pH (> 6) only small changes were seen when salts were added. When CaCl2 was added to a solution containing 7 M urea at pH 2.5, the self-association of the peptide increased with the concentration of CaCl2. Therefore, the salt dependent self-association observed in aqueous solvents was present in 7 M urea. Residues 45-76 in this GHRH analog, which are not present outside the hypothalamus, are probably needed to interact with a folding chaperone in vivo and provide stability for successful membrane transport and maintenance of biological activity.
authors.affiliation: Eli Lilly and Company, Greenfield, IN 46140, USA.
authors.forename: G F
authors.initials: GF
authors.lastname: Needham
authors.forename: A H
authors.initials: AH
authors.lastname: Pekar
authors.forename: H A
authors.initials: HA
authors.lastname: Havel
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004926:Escherichia coli / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000031:analogs & derivatives* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000096:biosynthesis / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D012492:Salts; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D014461:Ultracentrifugation
chemical_list: D010446:Peptide Fragments; D012492:Salts; D013007:Growth Hormone-Releasing Hormone