The structural basis of function in Cys-loop receptors

Abstract

Abstract. Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT 3 , GABA A and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT 3 ) and some are anion selective (e.g. GABA A and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT 3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.

Subunit stoichiometry and arrangement in a heteromeric glutamate-gated chloride channel

“…Hence, an alternative methodology must be considered. In Cys-loop receptors, the neurotransmitter-binding pockets lie at the interface between adjacent subunits (1)(2)(3)(4)(5)(6)(7)(8)(9). One could therefore use site-specific mutagenesis and biophysical characterization of activation mechanisms in recombinant receptors to find the types of subunits that line the agonist-binding pockets.…”

“…They belong to the Cys-loop receptor superfamily of transmembrane oligomers that open an intrinsic cationic or anionic channel pore upon binding of neurotransmitters, such as ACh, serotonin, GABA, Gly, histamine, or Glu (1)(2)(3)(4)(5)(6)(7)(8)(9). GluClRs are specific targets for ivermectin (IVM), a broad-spectrum anthelmintic drug used to treat filarial diseases like onchocerciasis (river blindness) and elephantiasis (lymphatic filariasis) that afflict hundreds of millions of people worldwide (10,11).…”

Synthesis and Characterization of Photoaffinity Probes that Target the 5-HT3 Receptor

“…Until now, a high-resolution crystal structure of the 5-HT 3 receptor has not been obtained and our knowledge of the binding cavity has largely been based on mutagenesis and homology with related proteins. [5] The aim of our project is the development of photoaffinity probes that can be used to covalently modify the 5-HT 3 receptor, and after subsequent enzymatic digestion, identify the orientation of the ligand in the binding pocket by mass spectrometry (Scheme 1).…”

Structural basis for cooperative interactions of substituted 2-aminopyrimidines with the acetylcholine binding protein

“…Ligand binding at two or more of the five intersubunit sites, located radially in the extracellular domain, drives a conformational change that results in the opening of a centrosymmetric transmembrane channel, internally constructed among the five subunits (SI Appendix, Fig. S2A) (1)(2)(3)(4). Up to five potential agonist-competitive antagonist sites on the pentamer are found at the outer perimeter of the subunit interfaces.…”

“…As revealed in functional studies, most nAChRs are heterooligomeric, where the sites of ligand occupation are not identical (1)(2)(3)(4). This arrangement arises when a common α-subunit pairs with one or more nonidentical subunit partners, termed non-α-subunits (7,8).…”