Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s Programmes at the University of Pécs and at the University of Debrecen Identification number: TÁMOP-4.1.2-08/1/A-2009-0011 Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s Programmes at the University of Pécs and at the University of Debrecen Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Tímea Berki and Ferenc Boldizsár Signal transduction EXTRACELLULAR RECEPTORS ION CHANNELS TÁMOP-4.1.2-08/1/A-2009-0011 Scheme of the signal transduction of cell surface receptors
Ligand Receptor
Intracellular signaling
Gene expression
Biological response TÁMOP-4.1.2-08/1/A-2009-0011 Receptor families
• Extracellular receptors: hidrophylic ligands eg. peptide, protein hormones – Ion-channel receptors – 7-transmembrane-spanning receptors (7TM) – Catalytic receptors: intrinsic enzyme activity – Non-catalytic receptors: use cytoplasmic tyrosine kinases • Intracellular receptors: lipophilic hormones eg. steroids, thyroxin
TÁMOP-4.1.2-08/1/A-2009-0011 Extracellular receptor types
ION-CHANNEL-LINKED RECEPTORS
Ions
Signal molecule Plasma membrane
Cytoplasm
G-PROTEIN-LINKED RECEPTORS
Signal molecule
g a g a a b Enzyme b Enzyme Enzyme GDP GTP GTP g G-protein Activated G-protein b Activated enzyme
ENZYME-LINKED RECEPTORS
Dimer of signal molecule Signal molecule
Enzyme
Inactive Active catalytic catalytic domain Activated enzyme domain TÁMOP-4.1.2-08/1/A-2009-0011 Receptors
Receptors
Ionotropic Metabotropic (ion-channel linked) (use second messengers)
GABAA, GABAC, iGlu GABAB, mGlu, Glycine, Adrenaline, Serotonin, Noradrenaline, Nicotinic Ach, Glucagon, FSH, LH, P2X TSH, ADH, parathormone, growth-factors, cytokines TÁMOP-4.1.2-08/1/A-2009-0011 More receptors using the same second messenger system
ACTH LH FSH Secretin Adrenaline Glucagon
Adenylyl cyclase ATP cAMP TÁMOP-4.1.2-08/1/A-2009-0011 Receptor - ligand interaction
Receptor properties Ligands 11-cis-retinal (in rhodopsin) Acetylcholine Ligand binds in the core region of the 7 Catecholamines transmembrane helices Biogenic amines (histamine, serotomine, etc.) Nucleosides and nucleotides Leukotrienes, prostaglandins, prostacyclins, Thromboxanes Short peptide ligands bind partially in the Peptide hormones (ACTH, glucagon, growth hormone) core region and to the external loops Parathyroid hormone, calcitonin Ligands make several contacts with the N- Hypothalamic glycoprotein releasing factors (TRH, terminal segment and the external loops GnRH) Metabotropic receptors for neurotransmitters (such as GABA and glutamate) Induce an extensive reorganization of an Ca2+-sensing receptors, for example on parathyroid cells, extended N-terminal segment thyroidal C-cells (which secrete calcitonin) and on the renal juxtaglomerular apparatus Proteinase activated receptors Receptors for thrombin amd thrypsin TÁMOP-4.1.2-08/1/A-2009-0011 Functional groups of ligands
Partial agonists and Inverse agonists antagonists Agonists
r R
Inactive state Active state
r R r R TÁMOP-4.1.2-08/1/A-2009-0011 Ionotropic receptors (ligand-gated ion channels)
Ions
Ligand Plasma membrane
Cytoplasm
Ligand gated ion channel TÁMOP-4.1.2-08/1/A-2009-0011 Ion channel receptors
• Cys-loop receptors: pentameric structure, 4 transmembrane (TM) regions/subunit – e.g., Acetylcholin (Ach) Nicotinic R – Na+ channel - – e.g., GABAA, GABAC, Glycine – Cl channels (inhibitory role in CNS) • Glutamate-activated cationic channels: (excitatory role in CNS), tetrameric stucture, 3 TM regions/subunit – e.g., iGlu • ATP-gated channels: 3 homologous subunits, 2 TM regions/subunit – e.g., P2X purinoreceptor
TÁMOP-4.1.2-08/1/A-2009-0011 Nicotinic Ach receptor
FRONT
TOP TÁMOP-4.1.2-08/1/A-2009-0011 Nicotinic Ach receptor
• Pore formed from 5 subunits: 2a, b, g, d • Opening: the 2a units are distorted • Desensitization: in the open conformation the b, g, d subunits become phosphorylated by Protein kinase A and C TÁMOP-4.1.2-08/1/A-2009-0011 The axon terminal
Axon of motor neuron
1 Axon terminal
Ca2+
2 Voltage-gated Ca2+ channel
Terminal button Vesicle of acethylcholine
3 Voltage-gated Na+ channel 5 K+ 6 4 Neurotransmitter-gated Acetylcholine channel 7 Acetylcholinesterase Na+ Motor end plate Muscle fiber ~4x107 nicotinic Ach Rs / end plate TÁMOP-4.1.2-08/1/A-2009-0011 Electric organs in animals
• Marine ray Torpedo • Freshwater electric eel Electrophorus • 2x1011 nicotinic Ach receptors/end plate!
TÁMOP-4.1.2-08/1/A-2009-0011 Blocking the neuromuscular transmission a-Bungarotoxin: • Snake venom (Bungarus multicinctus) • Binds to the N-Ach receptor and inactivates Curare (tubocurarin): • In South American plants Strychnos toxifera and Chondrodendron tomentosum • Indians use as arrow poison • Curare binds to the same place on the N-Ach receptor than Achetylcholin BUT channel doesn’t open • Causes paralysis of breathing muscles • Used as muscle relaxant in anaesthesia • Antidote: Acetylcholinesterase inhibitors
TÁMOP-4.1.2-08/1/A-2009-0011 Acetylcholinesterase (AchE)
• Quick removal of Ach from the synaptic space • Ach → choline+acetyl • Reversible inhibitors: therapeutic use (myasthenia, glaucoma, Alzheimer’s) • Irreversble inhibitors: chemical weapons and pesticides e.g. organophosphates Ach
AchE