Design and Synthesis of Photoaffinity-Labeling Ligands of thel-Prolyl-l-leucylglycinamide Binding Site Involved in the Allosteric Modulation of the Dopamine Receptor

Abstract

Pro-Leu-Gly-NH 2 (PLG), in addition to its endocrine effects, possesses the ability to modulate dopamine D 2 receptors within the CNS. However, the precise binding site of PLG is unknown. Potential photoaffinity labeling ligands of the PLG binding site were designed as tools to be used in the identification of the macromolecule that possesses this binding site. Six different photoaffinity labeling ligands were designed and synthesized based upon γ-lactam PLG peptidomimetic 1. The 4-azido-benzoyl and 4-azido-2-hydroxy-benzoyl photoaffinity labeling moieties were placed at opposite ends of PLG peptidomimetic 1 to generate a series of ligands that potentially could be used to map the PLG binding site. All of the compounds that were synthesized possessed activity comparable to or better than PLG in enhancing [ 3 H]N-propylnorapomorphine agonist binding to dopamine receptors. Photoaffinity ligands that were cross-linked to the receptor preparation produced a modulatory effect that was either comparable to or greater than the increase in agonist binding produced by the respective ligands that were not cross-linked to the dopamine receptor. The results indicate that these photoaffinity labeling agents are binding at the same site as PLG and PLG peptidomimetic 1.

Structure-Based Ligand Discovery Targeting Orthosteric and Allosteric Pockets of Dopamine Receptors

“…though its allosteric binding mode is not clear. Several analogs of the endogenous neuropeptide Pro-Leu-Gly-NH2 (Fisher et al, 2006;Bhagwanth et al, 2012) were previously reported to have either positive or negative allosteric effects on dopamine signaling. Binding modes of these peptidomimetics are also unknown, though it might be interesting to consider a possibility of their binding in the same region as the allosteric small molecules 23 and 26, amides of which have prominent interactions with the peptide backbone of ECL2 in our models.…”

Synthesis and biological evaluation of indole-2-carboxamides bearing photoactivatable functionalities as novel allosteric modulators for the cannabinoid CB1 receptor

“…In the absence of a crystal structure of the receptor, an alternative approach is to identify the ligand binding domain by using a methodology that involves labeling the receptor with photoaffinity ligands followed by mass spectrometry-based proteomic studies [18]. This methodology has been successfully applied to the identification of the allosteric binding sites of nicotinic acetylcholine receptors (nAChRs) [19, 20], M1 muscarinic acetylcholine receptor [21], dopamine D 2 receptors [22], GABA A receptor [23], and allosteric binding sites of other proteins [24–26]. Notably, the orthosteric binding domains of cannabinoid CB1 and CB2 receptors have been investigated using similar methodology [27, 28].…”

Change in expression of vesicular protein synapsin II by chronic treatment with D2 allosteric modulator PAOPA

“…Our previous studies [3,21,28,30,42] have developed a wide range of ligands to modulate D2R, a target which is strongly implicated in the etiology of schizophrenia. These ligands have been designed based on the functional pharmacophore of the endogenous tripeptide l-prolyl-l-leucyl glycinamide (PLG, also known as melanocyte-inhibiting factor-1 [MIF-1]), and have been shown to modulate dopamine binding via interaction with an allosteric site on the D2R [34].…”