Model of the extracellular domain of the human alpha7 nAChR based on the crystal structure of the mouse alpha1 nAChR extracellular domain

Schizophrenia: synthetic strategies and recent advances in drug design

Schizophrenia is a complex and unpredictable mental disorder which affects several domains of cognition and behaviour. It is a heterogeneous illness characterised by positive, negative, and cognitive symptoms, often accompanied by signs of depression. In this tutorial review, we discuss recent progress in understanding the target sites and mechanisms of action of second-generation antipsychotic drugs. Progress in identifying and defining target sites has been accelerated recently by advances in neuroscience, and newly developed agents that regulate signalling by the main excitatory neurotransmitters in the brain are surveyed. Examples of novel molecules for the treatment of schizophrenia in preclinical and clinical development and their industrial sponsors are highlighted.

Expression of water-soluble, ligand-binding concatameric extracellular domains of the human neuronal nicotinic receptor alpha4 and beta2 subunits in the yeast Pichia pastoris: glycosylation is not required for ligand binding

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation channels that are responsible for cell communication via the neurotransmitter acetylcholine. The predominant nAChR subtype in the mammalian brain with a high affinity for nicotine is composed of α4 and β2 subunits. This nAChR subtype is responsible for addiction to nicotine and is thought to be implicated in Alzheimer and Parkinson diseases and therefore presents an important target for drug design. In an effort to obtain water-soluble, ligand-binding domains of the human α4β2 nAChR for structural studies, we expressed the extracellular domains (ECDs) of these subunits in the eukaryotic expression system Pichia pastoris. The wild-type ECDs and their mutants containing the more hydrophilic Cys-loop from the snail acetylcholine-binding protein (individually expressed or coexpressed) did not demonstrate any specific interaction with ligands. We then linked the mutated ECDs with the 24-amino acid peptide (AGS)(8) and observed that the β2-24-α4 ECD concatamer, but not the α4-24-β2 one, exhibited very satisfactory water solubility and ligand binding properties. The (125)I-epibatidine and [(3)H]nicotine bound to β2-24-α4 with dissociation constants (K(d)) of 0.38 and 19 nm, respectively, close to the published values for the intact α4β2 AChR. In addition, (125)I-epibatidine binding was blocked by nicotine, cytisine, acetylcholine, and carbamylcholine with inhibition constants (K(i)) of 20.64, 3.24, 242, and 2,254 nm, respectively. Interestingly, deglycosylation of the concatamer did not affect its ligand binding properties. Furthermore, the deglycosylated β2-24-α4 ECD existed mainly in monomeric form, thus forming an appropriate material for structural studies and possibly for pharmacological evaluation of novel α4β2 nAChR-specific agonists.

Computational modeling study of human nicotinic acetylcholine receptor for developing new drugs in the treatment of alcoholism

Alcohol abuse and alcoholism are serious and costly problem in USA. Thus, the development of anti-alcoholism agents could be very significant. The understanding of the neurochemical basis underlying the addictive properties of drugs of abuse is imperative for the development of new pharmacological means to reverse the addictive state, prevent relapse or to reduce the intake of addictive compounds. The nicotinic acetylcholine receptors (nAChRs) are important therapeutic targets for various diseases. Recent studies have revealed that the alpha3beta2, alpha3beta3, and alpha6 subunits of nAChR protein family might be pharmacological targets for developing new drugs in the treatment of alcoholism. We have performed computational homology modeling of the alpha3beta2, alpha3beta3, and alpha6 subunits of human nACHRs based upon the recently determined crystal structure of the extracellular domain (ECD) of the mouse nAChR alpha1 subunit complexed with alpha-bungarotoxin at 1.94 A resolution. For comparison, we also built the ECD models of alpha4beta2, and alpha7 subunits of human nACHRs which are neurochemical targets for cessation of smoking. The three-dimensional (3D) models of the ECD of the monomer, and pentamer of these human nAChR were constructed. The docking of the agonist in the ligand-binding pocket of the human nAChR dimers was also performed. Since the nAChR ligand-binding site is a useful target for mutagenesis studies and the rational design of drugs against various diseases, these models provide useful information for future investigation.

Nicotinic receptors: allosteric transitions and therapeutic targets in the nervous system

Nicotinic receptors - a family of ligand-gated ion channels that mediate the effects of the neurotransmitter acetylcholine - are among the most well understood allosteric membrane proteins from a structural and functional perspective. There is also considerable interest in modulating nicotinic receptors to treat nervous-system disorders such as Alzheimer's disease, schizophrenia, depression, attention deficit hyperactivity disorder and tobacco addiction. This article describes both recent advances in our understanding of the assembly, activity and conformational transitions of nicotinic receptors, as well as developments in the therapeutic application of nicotinic receptor ligands, with the aim of aiding novel drug discovery by bridging the gap between these two rapidly developing fields.

Recent advances in understanding the structure of nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs), members of the Cys-loop ligand-gated ion channels (LGICs) superfamily, are involved in signal transduction upon binding of the neurotransmitter acetylcholine or exogenous ligands, such as nicotine. nAChRs are pentameric assemblies of homologous subunits surrounding a central pore that gates cation flux, and are expressed at the neuromuscular junction and in the nervous system and several nonneuronal cell types. The 17 known nAChR subunits assemble into a variety of pharmacologically distinct receptor subtypes. nAChRs are implicated in a range of physiological functions and pathophysiological conditions related to muscle contraction, learning and memory, reward, motor control, arousal, and analgesia, and therefore present an important target for drug research. Such studies would be greatly facilitated by knowledge of the high-resolution structure of the nAChR. Although this information is far from complete, important progress has been made mainly based on electron microscopy studies of Torpedo nAChR and the high-resolution X-ray crystal structures of the homologous molluscan acetylcholine-binding proteins, the extracellular domain of the mouse nAChR alpha1 subunit, and two prokaryotic pentameric LGICs. Here, we review some of the latest advances in our understanding of nAChR structure and gating.

Design and expression of human alpha7 nicotinic acetylcholine receptor extracellular domain mutants with enhanced solubility and ligand-binding properties

In order to facilitate structural studies of the extracellular domain (ECD) of human alpha7 nicotinic acetylcholine receptor (nAChR), we designed several mutants, since the wild-type-ECD forms large oligomers and microaggregates, and expressed them in the yeast Pichia pastoris. Mutant design was based on a 3D model of human alpha7-nAChR-ECD, constructed using as templates the X-ray crystal structure of the homologous acetylcholine-binding protein (AChBP) and the electron microscopy structure of the Torpedo alpha-nAChR-ECD. At least one mutant, mut10, carrying six single-point mutations (Phe3Tyr, Val69Thr, Cys116Ser, Ile165Thr, Val177Thr, Phe187Tyr) and the replacement of its Cys-loop with the corresponding and more hydrophilic AChBP Cys-loop, was expressed with a 4-fold higher expression yield (1.2 mg/L) than the wild-type alpha7-ECD, existing exclusively as a soluble oligomeric, probably pentameric, form, at concentrations up to at least 10 mg/mL, as judged by gel filtration and dynamic light scattering. This mutant displayed a significantly improved (125)I-alpha-bungarotoxin-binding affinity (K(d)=24 nM) compared to the wild-type-ECD (K(d)=70 nM), the binding being inhibited by unlabelled alpha-bungarotoxin, d-tubocurarine or nicotine (K(i) of 21.5 nM, 127 microM and 17.5 mM, respectively). Circular dichroism studies of mut10 revealed (a) a similar secondary structure composition ( approximately 5% alpha-helix, approximately 45% beta-sheet) to that of the AChBP, Torpedo alpha-nAChR-ECD, and mouse alpha1-nAChR-ECD, (b) a well-defined tertiary structure and (c) binding of small cholinergic ligands at micromolar concentrations. Furthermore, electron microscopy showed well-assembled, probably pentameric, particles of mut10. Finally, since deglycosylation did not alter its solubility or ligand-binding properties, mut10, in either its glycosylated or deglycosylated form, is a promising alpha7-ECD mutant for structural studies, useful for the rational drug design to treat alpha7-nAChR-related diseases.