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Transmembrane (cell surface) receptors
See also Membrane proteins.
Ion channel-linked (ionotropic) receptors
These receptors are typically the targets of fast neurotransmitters such as acetylcholine (nicotinic) and GABA; activation of these receptors results in changes in ion movement across a membrane.
5-HT3 receptor
The receptor is bullet-shaped and consists of five subunits (A-E) that form an oligomer. In the center of this pentamer of subunits is a ligand-gated ion channel full of water, which the five subunits enclose pseudo-symmetrically. Each subunit of the 5-HT3 receptor consists of three regions; the extracellular region, the transmembrane region, and the intracellular region[2].
The is relatively large compared to the other two regions, and contains a short C-terminus and a larger N-terminus. The N-terminus of the extracellular region is where the ligand binding occurs, and therefore deals with the agonists and antagonists[3].
These are located between two bordering subunits, assembled from three alpha-helices of one subunit and three beta-strands from the other subunit. Such connection creates a binding pocket with a small, select number of residues from each subunit pointed into the binding pocket, as opposed to the large remainder of residues that are pointing from the binding pocket[4]. This binding pocket shrinks around agonists, encapsulating them, and widens around antagonists, repulsing them.
The is within the C-terminus region, and contains four alpha-helical domains within it (M1-M4) that stretch the length of this inner, transmembrane area. These four alpha-helical domains conduct the channel openings via ion selectivity, depending on both charge and size[4]. M2, the porous domain, contains rings of charged amino acids at both its start and its , accounting for M2’s main contribution to ion selectivity. The M3 and M4 alpha-helices create a large with one another, thus assembling the [2].
The extracellular subunit interface of the 5-HT3 receptors: a computational alanine scanning mutagenesis study[5]
The serotonin type-3 receptor (5-HT3-R) is a cation selective transmembrane protein channel that belongs to the Cys–loop Ligand-Gated Ion Channel (LGIC) superfamily (http://www.ebi.ac.uk/compneur-srv/LGICdb/LGICdb.php), which also includes receptors for nicotinic acetylcholine (, PDB code 2bg9), γ-aminobutyric acid and glycine. 5-HT3-R is involved in signal transmission in the central and peripheral nervous system and its malfunctioning leads to neurodegenerative and psychiatric diseases, therefore it is an important target for drug design research. A few drugs active against 5-HT3-R are already on the market, such as, for example, palonosetron (http://en.wikipedia.org/wiki/Palonosetron) and granisetron (http://en.wikipedia.org/wiki/Granisetron).
The 5-HT3R is made of five monomers assembled in a to form an ion channel permeable to small ions (Na+, K+); each subunit contains three domains: an (shown on the example of nAChR, 2bg9). To date, five different 5-HT3-R subunits have been identified, the 5-HT3 A, B, C, D and E; however, only subunits A and B have been extensively characterised experimentally. The of nAChR is located at the extracellular region, at the interface between two monomers (α-γ and α-δ; 2 identical α monomers, chains A and D, are colored in same color - lavender), called the principal and the complementary subunits.
The 3D structure of 5-HT3-R has not been experimentally solved yet; however, it has been obtained computationally by means of homology modelling techniques. (http://salilab.org/modeller/)
Thus, the are modelled by homology with the 3D structure of the nAChR subunit A (2bg9-A) and are used to assemble receptor structures as pseudo-symmetric pentamers made either of or of in a still debated arrangement.[6] Subunits A and B are colored in magenta and red, respectively.
A complete characterization of the extracellular moiety of the (AA dimer is shown, principal subunit is colored in cyan and complementary is in blue, is obtained by the Computational Alanine Scanning Mutagenesis (CASM) approach [7], which simulates the substitution, one by one, of all the amino acid residues at the subunit-subunit interfaces with an Ala, thus to assess the interface binding contribution of single residue side-chains. The are classified as “hot spots” that stabilize the interface by more than 4 kcal/mol and “warm spots” that contribute to interface stabilization by more than 2 kcal/mol. Interface residues are shown in spacefill representation, hot spot residues are colored in red and warm spots residues are are in orange.
From this analysis the located at the interface core and formed by residues W178 (principal subunit), Y68, Y83, W85 and Y148 (complementary subunit) is highlighted.[8] In addition, two important groups of interface residues are probably involved in the coupling of and binding to channel activation/inactivation: W116-H180-L179-W178-E124-F125 (principal subunit) and Y136-Y138-Y148-W85-(P150) (complementary subunit), where W178 and Y148 appear to be critical residues for the binding/activation mechanism. Finally, the (principal subunit of AA is colored in cyan, principal subunit BB is colored in darkmagenta, complementary subunit AA is in blue and complementary subunit BB is in magenta) shows differences which could explain the reasons why the homopentamer 5-HT3B-R, if expressed, is not functional.[9]
The receptor is a transmembrane pentameric glycoprotein. It has a weight of approximately 300,000 Daltons. It cylindrical in appearance by electron microscopy approximately 16nm in length and 8nm in diameter. The main ion channel is composed of a water pore that runs through the entire length of the protein. If viewed from the synaptic cleft, the protein will look like a pseudo-symmetrical rosette shown in the picture below composed of 10 different alpha and 4 different beta subunits.
When cobra venom is introduced into the body is moves along the bloodstream to a diaphragm muscle. It works as a postsynaptic neurotoxin binding to the receptor as an extracellular ligand by interacting with OH group leaving the acetyl choline channel open which releases ions used in creating an action potential. Without the ions the diaphragm muscle can not be activated to contract and will not move so an individual can not take a breath. There must be five molecules of cobra toxin (red) to block the receptor (blue) as each molecule binds with an individual alpha chain on the acetylcholine receptor. This molecule was generated by overlaying the receptor and venom using Swiss PDB viewer magic fit. The RMS (root mean square difference) of this overlay if 12.21 angstroms involving 185 different atoms. The second image depicts an individual toxin binding with one chain on the receptor, both in the same color.
This representation shows each molecule of the .
Full view of the glutamate receptor shows the overall structure (amino-terminal, ligand-binding and transmembrane domains) in both (MF) and models.
Zooming in at the top of the receptor () (RCB) one can view the amino terminal domain, which is a part of the extracellular domain. This domain is implicated in receptor assembly, trafficking, and localization.
Moving toward the bottom of the receptor () (SM) one can view the transmembrane domain. Here is the same domain separated from the rest of the protein..(DM) This domain widens in response to glutamate binding allowing for positive ions to pass through the post-synaptic membrane.
This view () highlights the area where a receptor antagonist, 2K200225, will bind.
Close up view of the ligand binding site ()(AH) of the endogenous ligand glutamate.
G protein-linked (metabotropic) receptors
This is the largest family of receptors and includes the receptors for several hormones and slow transmitters(dopamine, metabotropic glutamate). They are composed of seven transmembrane alpha helices. The loops connecting the alpha helices form extracellular and intracellular domains. The binding-site for larger peptide ligands is usually located in the extracellular domain whereas the binding site for smaller non-peptide ligands is often located between the seven alpha helices and one extracellular loop. These receptors are coupled to different intracellular effector systems via G proteins
- G protein-coupled receptors
- Neurotensin receptor
- CXC chemokine receptor type 4
- Mu Opioid Receptor Bound to a Morphinan Antagonist
- μ Opioid Receptors
- Mu Opioid Receptor
- The κ-opioid receptor binds opium-type ligands. For details see Student Project 3 for UMass Chemistry 423 Spring 2015.
- T The δ-opioid receptor binds enkephalins. For details see Delta opioid receptor
- Tutorial: The opioid receptor, a molecular switch
- Orexin and Orexin receptor
- Belsomra and Orexin receptors
- Hypocretin and receptors
- Human Follicle-Stimulating Hormone Complexed with its Receptor
- GPR40
- Lysophosphatidic acid receptor
- Sphingosine 1-phosphate Receptor
- Rhodopsin
- Rhodopsin Structure and Function
- Serotonin receptors, main page
- 3D structures of Serotonin receptors
- Adrenergic receptors in general
- Beta-1 Adrenergic receptor
- Dobutamine, see Beta-1 Adrenergic receptor, 2y00, 2y01, 6h7l
- Isoprenaline, see Beta-1 Adrenergic receptor, 2y03
- Carmoterol, see 2y02
- Salbutamol (Albuterol in USA), 2y04
- The human β2 adrenergic receptor bound to a G-protein (3sn6) is featured in a scene above, and additional structures are on the Adrenergic receptor page.
- Article Beta-2 Adrenergic Receptor by Wayne Decatur, David Canner, Dotan Shaniv, Joel L. Sussman, Michal Harel
- Article Beta-2 adrenergic receptor by Joel L. Sussman, Tala Curry, Michal Harel, Jaime Prilusky
- Group:SMART:A Physical Model of the beta-Adrenergic Receptor
- Gs: adenylate cyclase activated, cAMP up. For Gs see Beta2 adrenergic receptor-Gs protein complex updated
- Dopamine receptors 1 page
- Dopamine receptors 2 page
- Histamine H1 receptor
- 3rze - human histamine H1 receptor with an antagonist doxepin
- Adenosine A2A receptor
- Effect of Caffeine (Trimethylxanthine) on Human A2A Receptor
- Adenosine A2A receptor 3D structures
- Muscarinic acetylcholine receptor
- Glucose-dependent Insulinotropic Polypeptide Receptor
- Glucagon receptor
- Glucagon-like peptide 1 receptor
- Metabotropic Glutamate Receptors
- Ligand Binding N-Terminal of Metabotropic Glutamate Receptors
- Metabotropic glutamate receptor 5
Kinase-linked, enzyme-linked and related receptors
Receptor tyrosine kinases
Receptor tyrosine kinases (RTKs) are part of the larger family of protein tyrosine kinases. They are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Approximately 20 different RTK classes have been identified.[10]
Immune receptors
Leukocyte immunoglobulin-like receptors
Cytokine receptors
TNF receptor superfamily
Type I cytokine receptors
Type II cytokine receptors
Interferon receptors
Interleukin receptors
Interleukin-20 receptor:
Chemokine receptors, two of which acting as binding proteins for HIV (CXCR4 and CCR5). They are G protein-coupled receptors
T-cell receptors
TGF-beta receptor
LDL receptor
Transferrin receptor
Intracellular receptors
Signal recognition particle receptor
Receptor for activated C kinase 1
Nuclear receptors
Endoplasmic reticulum/Sarcoplasmic reticulum receptors
Ligand-gated Calcium channels
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