Surface properties of an amphiphilic peptide hormone and of its analog: corticotropin-releasing factor and sauvagine.

Abstract

Synthetic corticotropin (adrenocorticotropic hormone)-releasing factor [CRF; for the sequence, see Vale, W., Spiess, J., Rivier, C. & Rivier, J. (1981) Science 213, 1394Science 213, -1397 in aqueous solution exists predominantly as a random coil. At concentrations greater than 1 ,uM, the peptide shows a tendency to self-aggregate with a concurrent slight increase in the apparent a-helical content as measured by the CD spectrum. The a-helix formed by this molecule is highly amphiphilic-i.e., the hydrophilic and hydrophobic regions are segregated on opposite faces of the helix. As predicted from the potential amphiphilic structure, CRF binds avidly to the surface of single bilayer egg phosphatidylcholine vesicles. This binding appears to obey a simple Langmuir isotherm with the following parameters: Kd = 1.3 + 0.6 x 10-7 M and capacity at saturation (N) = 11.0 -1.0 mmol of peptide per mol of phospholipid. CRF also readily forms an insoluble monolayer at the air-water interface. The monolayer is composed of monomers of the hormone with molecular areas, A' = 22 A2 per amino acid, suggesting a compact secondary structure. judged from the collapse pressure (19.0 ± 0.1 dyne/cm; 1 dyne = 10 ,uN) of the monolayer, the amphiphilicity of CRF approximates that of plasma apolipoproteins, a class of proteins of the most pronounced amphiphilic character. These results suggest that the binding of CRF to the cell membrane is accompanied by the induction of an ahelical secondary structure and it is this predominantly helical form that is the biologically active form of the peptide.Corticotropin (adrenocorticotropic hormone)-releasing factor (CRF) is a hormone produced by the hypothalamus; it increases the rate of secretion of corticotropin by the pituitary gland (1, 2). The primary structure of ovine CRF has been determined by Vale et al. (3) and is shown in Fig. 1. Vale et al. also reported that a considerable portion of CRF is highly homologous to sauvagine, a peptide isolated from the skin of the South American frog Phylomedusa sauvagei and to urotensin I (4).The homology appears to be more conservative toward the amino and carboxyl termini of the molecule, whereas the pentapeptide segment of residues 24-28 in CRF, located toward the center of the chain, seems to be dissimilar. Analysis of the helical potential of CRF by the method of Chou and Fasman (5) indicated that two large sections of the molecule have very pronounced a-helical potential. When the amino acid sequence of the two regions of high helical potential is projected axially using the "Edmundson wheel" (6), the hydrophilic and hydrophobic residues appear to be segregated on opposite sides of the cylindrical helix, as shown in Fig. 1. The hydrophilic and hydrophobic domains on these a-helices are not of equal importance: the hydrophobic domain is almost twice as large as the hydrophilic one. The occurrence of regions of high amphiphilic a-helical potential in CRF is not unique to this hormone: in fact, several peptide hormones of intermediate size (i....

Infrared spectroscopic evidence of conformational transitions of an atrial natriuretic peptide.

“…The observed propensity of atriopeptin III to adopt a highly ordered 1-structure in such an environment is likely to be of direct relevance to the mechanism of the receptor-hormone recognition process. This is in accord with the hypothesis that the lipid phase of the target cell surface may facilitate the correct folding of the peptide hormones prior to their interaction with the receptor (23,(25)(26)(27).…”

“…The ability of atriopeptin III to undergo conformational transitions upon binding to phospholipid membranes may be of particular significance. It has been suggested that lipid affinity plays a role in the receptor binding of many peptide hormones (22)(23)(24)(25)(26)(27). The biological action of atrial natriuretic factors is mediated by a specific hormone-receptor interaction that occurs not in aqueous medium but in the amphiphilic membrane environment (28).…”

A single amino acid serves as an affinity switch between the receptor and the binding protein of corticotropin-releasing factor: Implications for the design of agonists and antagonists

“…By using CD (28) and NMR (29, 30) spectroscopic methods, evidence has been provided that CRF forms an amphiphilic helix whose hydrophobic patch binds to hydrophobic surfaces (31). On the basis of the helical wheel diagrams for the central parts of the peptides Svg (28) and h͞rCRF (Fig.…”

The Prevention of Preterm Labour - Corticotropin Releasing Hormone Type 1 Receptors as a Target for Drug Design and Development

“…20 A further SAR study, utilising an alanine replacement series of ovine CRH, found that the side chains of residues 5-19, in the N-terminal region, are important for receptor binding and activation. 22 C-Terminal amino acid residues are more responsible for structural conservation than for functional expression. The α-helix formed by CRH upon binding is highly amphiphilic in nature with hydrophobic and hydrophilic regions segregated on opposite faces of the helix.…”

“…20,22 The first 8 residues are important for activation, whereas the hydrophobic side chains from amino acids 15-19 are crucial for activation of the receptor as well as its binding, the remainder of 6 the C terminus is involved in binding and is required in its entirety for full potency. 20 The C-terminal region is responsible for the formation of the α-helix.…”