Needham GF, Pekar AH, Havel HA. Effect of salts on the structure of a potent analog of growth hormone releasing hormone as determined by optical spectroscopy.
J Pharm Sci 1995;
84:437-42. [PMID:
7629733 DOI:
10.1002/jps.2600840410]
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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.
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