Information about Acetylcholine Receptor
An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of the neurotransmitter acetylcholine.
Binding of acetylcholine to the N termini of each of the two alpha subunits results in the 15° rotation of all M2 helices[1]. This activates the channel, allowing for influx of Na+ and the efflux of K+. The cytoplasm side of the nAChR receptor has rings of high negative charge that determine the specific cation specificity of the receptor and remove the hydration shell often formed by ions in aqueous solution. In the intermediate region of the receptor, within the pore lumen, valine and leucine residues (Val 255 and Leu 251) define a hydrophobic region which the dehydrated ion must pass through[2].
nAChR is found at the edges of junctional folds at the neuromuscular junction on the postsynaptic side, and is activated by acetylcholine release across the synapse. The diffusion of Na+ and K+ across the receptor causes depolarization, the end-plate potential, that opens voltage-gated sodium channels, which allows for firing of the action potential and potentially muscular contraction.
Nicotinic receptors are the primary mediator of the effects of nicotine. In myasthenia gravis, the receptor is targeted by antibodies, leading to muscle weakness. Muscarinic acetylcholine receptors can be blocked by the drugs atropine and scopolamine.
Classification
Like other transmembrane receptors, acetylcholine receptors are classified according to their "pharmacology", or according to their relative affinities and sensitivities to different molecules. Although all acetylcholine receptors, by definition, respond to acetylcholine, they respond to other molecules as well.- nicotinic acetylcholine receptors (nAChR, also known as "ionotropic" acetylcholine receptors) are particularly responsive to nicotine
- muscarinic acetylcholine receptors (mAChR, also known as "metabotropic" acetylcholine receptors) are particularly responsive to muscarine.
Receptor types
Molecular biology has shown that the nicotinic and muscarinic receptors belong to distinct protein superfamilies.nAChR
The nAChRs are ligand-gated ion channels, and, like other members of the "cys-loop" ligand-gated ion channel superfamily, are composed of five protein subunits symmetrically arranged like staves around a barrel. The subunit composition is highly variable across different tissues. Each subunit contains four regions named M1, M2, M3, and M4, which span the membrane and consist of approximately 20 amino acids. The M2 region, which sits closest to the pore lumen, forms the pore lining.Binding of acetylcholine to the N termini of each of the two alpha subunits results in the 15° rotation of all M2 helices[1]. This activates the channel, allowing for influx of Na+ and the efflux of K+. The cytoplasm side of the nAChR receptor has rings of high negative charge that determine the specific cation specificity of the receptor and remove the hydration shell often formed by ions in aqueous solution. In the intermediate region of the receptor, within the pore lumen, valine and leucine residues (Val 255 and Leu 251) define a hydrophobic region which the dehydrated ion must pass through[2].
nAChR is found at the edges of junctional folds at the neuromuscular junction on the postsynaptic side, and is activated by acetylcholine release across the synapse. The diffusion of Na+ and K+ across the receptor causes depolarization, the end-plate potential, that opens voltage-gated sodium channels, which allows for firing of the action potential and potentially muscular contraction.
mAChR
In contrast, the mAChRs are not ion channels, but belong instead to the superfamily of G-protein-coupled receptors that activate other ionic channels via a second messenger cascade.Role in health and disease
Nicotinic acetylcholine receptors can be blocked by curare and toxins present in the venoms of snakes and shellfishes. Drugs such as the neuromuscular blocking agents bind reversibly to the nicotinic receptors in the neuromuscular junction and are used routinely in anaesthesia.Nicotinic receptors are the primary mediator of the effects of nicotine. In myasthenia gravis, the receptor is targeted by antibodies, leading to muscle weakness. Muscarinic acetylcholine receptors can be blocked by the drugs atropine and scopolamine.
External links
The muscarine cholinergic receptor activates a G protein when bound to ex.c. ach. The alpha subunit of the Gprotein deactivates adenylate cyclase while the betagamma subunit activates the Kchannels and therefore hyperpolarise the cell. This causes a decrease in cardiac activity.References
Ion channel, receptor: ligand-gated ion channels | |
|---|---|
| Cys-loop receptors | Glycine receptor - GABA receptor (GABA A, GABA C) - 5-HT receptor (5-HT3 serotonin receptor) - Acetylcholine receptor (Nicotinic acetylcholine receptor) |
| Ionotropic glutamate receptors | NMDA - Kainate - AMPA |
| ATP-gated channels | Purinergic receptors (P2X) |
An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes denaturing agents.
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Neurotransmitters are chemicals that are used to relay, amplify and modulate signals between a neuron and another cell. According to the prevailing beliefs of the 1960s, a chemical can be classified as a neurotransmitter if it meets the following conditions:
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The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. It is a chemical transmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms including humans.
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Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cell's plasma membrane, but also in the membranes of some subcellular compartments and organelles.
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Nicotinic acetylcholine receptors, or nAChRs, are ionotropic receptors that form ligand gated ion channels in cells' plasma membranes. Like the other type of acetylcholine receptors, muscarinic acetylcholine receptors (mAChRs), their opening is triggered by the
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The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are opened or closed in response to binding of a chemical messenger, as opposed to voltage-gated ion channels or
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Nicotine is an alkaloid found in the nightshade family of plants (Solanaceae), predominantly in tobacco, and in lower quantities in tomato, potato, eggplant (aubergine), and green pepper. Nicotine alkaloids are also found in the leaves of the coca plant.
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Muscarinic receptors are those membrane-bound acetylcholine receptors that are more sensitive to muscarine than to nicotine. Those for which the contrary is true are known as nicotinic acetylcholine receptors. Muscarine and nicotine are both alkaloids.
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metabotropic and ionotropic receptors. In contrast to the latter, metabotropic receptors do not form an ion channel pore; rather, they are indirectly linked with ion-channels on the plasma membrane of the cell through signal transduction mechanisms.
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Muscarine, L -(+)-muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. It was first isolated from Amanita muscaria in 1869.
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Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell,
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as
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The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are opened or closed in response to binding of a chemical messenger, as opposed to voltage-gated ion channels or
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Ion channels are pore-forming proteins that help to establish and control the small voltage gradient across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient.
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The Cys-loop ligand-gated ion channel superfamily is comprised of nicotinic acetylcholine, GABAA, GABAC, glycine and 5-HT3 receptors that are composed of five protein subunits and possess a characteristic loop formed by a disulphide bond between two
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The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are opened or closed in response to binding of a chemical messenger, as opposed to voltage-gated ion channels or
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In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or "coassembles") with other protein molecules to form a multimeric or oligomeric protein.
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Sodium (IPA: /ˈsəʊdiəm/) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1.
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Potassium (IPA: /pə(ʊ)ˈtasiəm/, /pə'tæsiəm/) is a chemical element. It has the symbol K (Arabic: al qalja
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Valine (abbreviated as Val or V)[1] is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)2. L-Valine is one of 20 proteogenic amino acids. Its codons are GUU, GUC, GUA, and GUG.
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Leucine (abbreviated as Leu or L)[1] is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH(CH3)2. It is an essential amino acid, which means that humans cannot synthesise it.
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neuromuscular junction (NMJ) is the synapse or junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately
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Sodium channels (also known as "voltage-gated sodium channels") are integral membrane proteins that conduct sodium ions (Na+) through a cell's plasma membrane. Many of the ionotropic receptors are also able to conduct sodium ions.
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An action potential is a "spike" of electrical discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants.
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G protein-coupled receptors (GPCRs), also known as seven transmembrane receptors, 7TM receptors, heptahelical receptors, and G protein linked receptors (GPLR
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In cell physiology, a secondary messenger system (also known as a second messenger system) is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change.
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Curare is a common name for various dart poisons (arrow poisons) originating from South America. The three main types, or families of curare are:
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- the tubocurare (also known as tube or bamboo curare, because of its packing into hollow bamboo tubes; main toxin is
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Serpentes
Linnaeus, 1758
Infraorders and Families
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Linnaeus, 1758
Infraorders and Families
- Alethinophidia - Nopcsa, 1923
- Acrochordidae- Bonaparte, 1831
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Shellfish is a culinary term for aquatic invertebrates used as food: molluscs, crustaceans, and echinoderms. Both saltwater and freshwater invertebrates are considered shellfish. Shellfish is a misnomer, because these invertebrates are definitely not fish.
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