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      Identification of novel α7 nicotinic receptor ligands by in silico screening against the crystal structure of a chimeric α7 receptor ligand binding domain

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          Abstract

          A hierarchical in silico screening procedure using the crystal structure of an agonist bound chimeric α7/Ls-AChBP protein was successfully applied to both proprietary and commercial databases containing drug-like molecules. An overall hit rate of 26% (p K i ⩾5.0) was obtained, with an even better hit rate of 35% for the commercial compound collection. Structurally novel and diverse ligands were identified. Binding studies with [ 3H]epibatidine on chimeric α7/5-HT 3 receptors yielded submicromolar inhibition constants for identified hits. Compared to a previous screening procedure that utilized the wild type Ls-AChBP crystal structure, the current study shows that the recently obtained α7/Ls-AChBP chimeric protein crystal structure is a better template for the identification of novel α7 receptor ligands.

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          Most cited references 19

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          Nicotine and carbamylcholine binding to nicotinic acetylcholine receptors as studied in AChBP crystal structures.

          Nicotinic acetylcholine receptors are prototypes for the pharmaceutically important family of pentameric ligand-gated ion channels. Here we present atomic resolution structures of nicotine and carbamylcholine binding to AChBP, a water-soluble homolog of the ligand binding domain of nicotinic receptors and their family members, GABAA, GABAC, 5HT3 serotonin, and glycine receptors. Ligand binding is driven by enthalpy and is accompanied by conformational changes in the ligand binding site. Residues in the binding site contract around the ligand, with the largest movement in the C loop. As expected, the binding is characterized by substantial aromatic and hydrophobic contributions, but additionally there are close contacts between protein oxygens and positively charged groups in the ligands. The higher affinity of nicotine is due to a main chain hydrogen bond with the B loop and a closer packing of the aromatic groups. These structures will be useful tools for the development of new drugs involving nicotinic acetylcholine receptor-associated diseases.
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            The alpha7 nicotinic acetylcholine receptor as a pharmacological target for inflammation.

            The physiological regulation of the immune system encompasses comprehensive anti-inflammatory mechanisms that can be harnessed for the treatment of infectious and inflammatory disorders. Recent studies indicate that the vagal nerve, involved in control of heart rate, hormone secretion and gastrointestinal motility, is also an immunomodulator. In experimental models of inflammatory diseases, vagal nerve stimulation attenuates the production of proinflammatory cytokines and inhibits the inflammatory process. Acetylcholine, the principal neurotransmitter of the vagal nerve, controls immune cell functions via the alpha7 nicotinic acetylcholine receptor (alpha7nAChR). From a pharmacological perspective, nicotinic agonists are more efficient than acetylcholine at inhibiting the inflammatory signaling and the production of proinflammatory cytokines. This 'nicotinic anti-inflammatory pathway' may have clinical implications as treatment with nicotinic agonists can modulate the production of proinflammatory cytokines from immune cells. Nicotine has been tested in clinical trials as a treatment for inflammatory diseases such as ulcerative colitis, but the therapeutic potential of this mechanism is limited by the collateral toxicity of nicotine. Here, we review the recent advances that support the design of more specific receptor-selective nicotinic agonists that have anti-inflammatory effects while eluding its collateral toxicity.
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              Neuronal nicotinic receptors: from structure to pathology.

              Neuronal nicotinic receptors (NAChRs) form a heterogeneous family of ion channels that are differently expressed in many regions of the central nervous system (CNS) and peripheral nervous system. These different receptor subtypes, which have characteristic pharmacological and biophysical properties, have a pentameric structure consisting of the homomeric or heteromeric combination of 12 different subunits (alpha2-alpha10, beta2-beta4). By responding to the endogenous neurotransmitter acetylcholine, NAChRs contribute to a wide range of brain activities and influence a number of physiological functions. Furthermore, it is becoming evident that the perturbation of cholinergic nicotinic neurotransmission can lead to various diseases involving nAChR dysfunction during development, adulthood and ageing. In recent years, it has been discovered that NAChRs are present in a number of non-neuronal cells where they play a significant functional role and are the pathogenetic targets in several diseases. NAChRs are also the target of natural ligands and toxins including nicotine (Nic), the most widespread drug of abuse. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining their regional and cellular localisation and the molecular basis of their functional diversity mainly in pharmacological and biochemical terms. The recent availability of mice with the genetic ablation of single or double nicotinic subunits or point mutations have shed light on the role of nAChRs in major physiological functions, and we will here discuss recent data relating to their behavioural phenotypes. Finally, the role of NAChRs in disease will be considered in some details.
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                Author and article information

                Journal
                Bioorg Med Chem
                Bioorg. Med. Chem
                Bioorganic & Medicinal Chemistry
                Elsevier Science
                0968-0896
                1464-3391
                01 October 2012
                01 October 2012
                : 20
                : 19
                : 5992-6002
                Affiliations
                [a ]Division of Pharmacology, Faculty of Pharmacy, Bezmialem Vakif University, Istanbul, Turkey
                [b ]Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems (AIMMS), VU University Amsterdam, The Netherlands
                [c ]Department of Biochemistry, University of Cambridge, Cambridge, UK
                Author notes
                [* ]Corresponding author. Tel.: +31 20 59 87841; fax: +31 20 5987610. i.de.esch@ 123456vu.nl
                [†]

                These authors contributed equally.

                Article
                BMC10163
                10.1016/j.bmc.2012.06.054
                3460237
                22959526
                © 2012 Elsevier Ltd.

                This document may be redistributed and reused, subject to certain conditions.

                Categories
                Article

                Pharmaceutical chemistry

                docking, achbp, in silico screening, α7 receptor, cys-loop, nachr, virtual screening

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