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The interactions of bivalent and trivalent ACTH analogs with ACTH receptors: Potency and mechanisms
Abstract
Adrenocorticotropin (ACTH), a polypeptide hormone containing 39 amino acid residues, acts on receptors located on the adrenal cell membrane to stimulate steroidogenesis. An intact sequence of amino acids 6-9 of the normal peptide is essential for activation of ACTH receptors. ACTH peptides lacking this intact sequence act as competitive antagonists. A series of bivalent ACTH peptides was prepared by bis(maleimide) crosslinking of carboxyl terminal cysteine sulfhydryl groups of synthetic ACTH peptides, Cys$\sp{25}$ACTH(7-25) and Cys$\sp{39}$ACTH(7-39). Some bivalent ACTH antagonists displayed much greater antagonist potency than their monovalent analogs. The level of potency enhancement was found to be dependent upon the spacer used to link receptor binding domains and the length of the ACTH peptide used in bivalent antagonist synthesis. Another series of multivalent ACTH antagonists was synthesized by reaction of combinations of C$\sp{25}$ACTH(7-25), C$\sp{25}$ACTH(11-25) and cysteine with a trivalent maleimide. The antagonists contained one, two, or three receptor binding sites. Tris (ACTH(7-25)) $\sb3$ was the most potent antagonist. To directly study the mechanism of the interaction of multivalent ACTH peptides with receptors, a bivalent ACTH agonist was prepared by cross-linking two F$\sp2$Nle$\sp4$C$\sp{39}$ACTH(1-39) peptides with a 20A bis(maleimide). The bivalent peptide was 25 times more potent on a molar basis in stimulation of steroidogenesis than its monovalent homolog. Binding studies showed a single class of receptor with high affinity for both ($\sp{125}$I) -F$\sp2$Nle$\sp4$C$\sp{39}$ACTH(1-39) succinimide and ($\sp{125}$I) -bis (F$\sp2$Nle$\sp4$C$\sp{39}$ACTH(1-39)) $\sb2$. It was concluded: (1) The potency enhancement observed with bivalent ACTH peptides is dependent on the length of the ACTH peptide component and is not due to direct interaction between the spacer and cell surface. (2) Multivalent ACTH antagonists can be prepared that are 50 times more potent on a molar basis then their monovalent homologs. (3) Bivalent agonists can be prepared that display substantially enhanced potency relative to their monovalent homologs. (4) The high affinity and selectivity of multivalent ACTH peptides result from receptor specific interactions and non-specific interactions.
Subject Area
Biochemistry
Recommended Citation
Lin, Chaomei, "The interactions of bivalent and trivalent ACTH analogs with ACTH receptors: Potency and mechanisms" (1991). ETD collection for University of Nebraska-Lincoln. AAI9133298.
https://digitalcommons.unl.edu/dissertations/AAI9133298