Aminergic Ligands Research Articles

A Novel and Functionally Diverse Class of Acetylcholine-Gated Ion Channels.

Fast cholinergic neurotransmission is mediated by acetylcholine-gated ion channels; in particular, excitatory nicotinic acetylcholine receptors play well established roles in virtually all nervous systems. Acetylcholine-gated inhibitory channels have also been identified in some invertebrate phyla, yet their roles in the nervous system are less well understood. We report the existence of multiple new inhibitory ion channels with diverse ligand activation properties in Caenorhabditis elegans We identify three channels, LGC-40, LGC-57, and LGC-58, whose primary ligand is choline rather than acetylcholine, as well as the first evidence of a truly polymodal channel, LGC-39, which is activated by both cholinergic and aminergic ligands. Using our new ligand-receptor pairs we uncover the surprising extent to which single neurons in the hermaphrodite nervous system express both excitatory and inhibitory channels, not only for acetylcholine but also for the other major neurotransmitters. The results presented in this study offer new insight into the potential evolutionary benefit of a vast and diverse repertoire of ligand-gated ion channels to generate complexity in an anatomically compact nervous system.SIGNIFICANCE STATEMENT Here we describe the diversity of cholinergic signaling in the nematode Caenorhabditis elegans We identify and characterize a novel family of ligand-gated ion channels and show that they are preferentially gated by choline rather than acetylcholine and expressed broadly in the nervous system. Interestingly, we also identify one channel gated by chemically diverse ligands including acetylcholine and aminergic ligands. By using our new knowledge of these ligand-gated ion channels, we built a model to predict the synaptic polarity in the C. elegans connectome. This model can be used for generating hypotheses on neural circuit function.

Structure-Based Consensus Scoring Scheme for Selecting Class A Aminergic GPCR Fragments.

Aminergic G-protein coupled receptors (GPRCs) represent well-known targets of central nervous-system related diseases. In this study a structure-based consensus virtual screening scheme was developed for designing targeted fragment libraries against class A aminergic GPCRs. Nine representative aminergic GPCR structures were selected by first clustering available X-ray structures and then choosing the one in each cluster that performs best in self-docking calculations. A consensus scoring protocol was developed using known promiscuous aminergic ligands and decoys as a training set. The consensus score (FrACS-fragment aminergic consensus score) calculated for the optimized protein ensemble showed improved enrichments in most cases as compared to stand-alone structures. Retrospective validation was carried out on public screening data for aminergic targets (5-HT1 serotonin receptor, TA1 trace-amine receptor) showing 8-17-fold enrichments using an ensemble of aminergic receptor structures. The performance of the structure based FrACS in combination with our ligand-based prefilter (FrAGS) was investigated both in a retrospective validation on the ChEMBL database and in a prospective validation on an in-house fragment library. In prospective validation virtual fragment hits were tested on 5-HT6 serotonin receptors not involved in the development of FrACS. Six out of the 36 experimentally tested fragments exhibited remarkable antagonist efficacies, and 4 showed IC50 values in the low micromolar or submicromolar range in a cell-based assay. Both retrospective and prospective validations revealed that the methodology is suitable for designing focused class A GPCR fragment libraries from large screening decks, commercial compound collections, or virtual databases.

Tartaric Acid Enhances Adrenergic Receptor Activity: Test of a General Theory of Extracellular Aminergic GPCR Enhancer Discovery.

Several different classes of compounds enhance the potency of aminergic receptor ligands three-fold or more and increase their duration of activity up to ten-fold. These enhancers include the vitamins ascorbic acid and folic acid, chelators such as ethylenediaminetetraacetic acid, corticosteroids, and opioids, opiates and opiate antagonists. We have previously demonstrated that all of these classes of enhancers share a common molecular motif consisting of a linear array of two hydroxyls and a carbonyl. We demonstrate here that because of this common molecular motif, all compounds known to enhance aminergic receptor ligands bind to highly conserved regions of the first or second extracellular loops of aminergic receptors at physiologically or pharmacologically relevant concentrations. These compounds also bind directly to aminergic ligands with significant specificity and affinity. These results suggest three very simple, complementary methods for screening for novel extracellular aminergic receptor enhancers: 1) in silico screening for the presence of the common aminergic receptor enhancer motif; 2) screening for binding to the aminergic ligand of choice; and 3) screening for binding to receptor peptides representing the enhancer binding site on the receptor. Using these three complementary methods, we predict a new class of enhancers (tartaric acids) and demonstrate the predicted enhancement in an in vitro smooth muscle assay.

Oral delivery of G protein-coupled receptor modulators: An explanation for the observed class difference

G protein-coupled receptors (GPCRs) represent important targets for drug intervention. However, analysis of GPCR modulator drugs exhibits an important class difference, with many drugs available against aminergic GPCR targets, but relatively few against non-aminergic targets. The reason for this is that commonly drugs mimic the physicochemistry of the receptor ligand. Aminergic ligands generally exhibit physicochemical properties (molecular weight, lipophilicity and hydrogen bonding potential) that are consistent with extensive oral absorption. In contrast, non-aminergic ligands generally exhibit physicochemical properties that are at odds with oral delivery. Thus, combining required potency versus the receptor, with oral delivery potential is a significant challenge, and drug discovery becomes a question of finding the exceptional compound that lies at the edge of ADME space.

The binding site of aminergic G protein-coupled receptors: the transmembrane segments and second extracellular loop.

In the current chapter, we review approaches to the identification of the residues forming the binding sites for agonists, antagonists, and allosteric modulators in the family of aminergic G protein-coupled receptors (GPCRs). We then review the structural bases for ligand binding and pharmacological specificity based on the application of these methods to muscarinic cholinergic, adrenergic, dopaminergic, serotonergic, and histaminergic receptors, using the high resolution rhodopsin structure as a template. Furthermore, we propose a critical role of the second extracellular loop in forming the binding site for small molecular weight aminergic ligands, much as this loop dives down into the binding-site crevice and contacts retinal in rhodopsin.

Behavioural pharmacology of dopamine, serotonin and putative aminergic ligands in the mushroom bodies of the honeybee ( Apis mellifera)

The proboscis extension response (PER) which can be elicited in bees by stimulating one antenna with water vapour, was used to quantify the effects of dopamine, serotonin (5-HT) and putative receptor ligands in the mushroom body of the bee. The drugs were microinjected into the α-lobe of the mushroom body in one brain hemisphere. Injection of dopamine reduces the water vapour-elicited PER significantly. The effects of dopamine are limited to the treated side. Injection of 5-HT has similar effects to dopamine. The effects of 5-HT are apparent on the treated and partly also on the contralateral side. Significant effects for dopamine on the treated side were found when the concentration in the injected drop was 10 −7 M. For 5-HT significant effects on the treated side were apparent for concentrations of 10 −8 M. Putative dopamine and 5-HT receptor ligands were injected alone and coinjected with the amines. Two ligands with dopamine-antagonistic effects were found: buspirone>spiperone, while lisuride, sulpiride, chlorpromazine, SCH 23390, butaclamol and haloperidol had no dopamine-antagonistic effects. All tested putative 5-HT receptor ligands had significant 5-HT-antagonistic effects: butaclamol>methysergide>lisuride>cyproheptadine>SCH 23390. Good correlations between the behavioural data and in vitro radioligand binding studies were found for 5-HT receptor ligands, while there exist only partial correlations for dopamine receptor ligands.