Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Selected examples on The Structure of Ion Channels Ion channels Classification by gating Voltage-gated channels Voltage-gated Na+, Ca2+ , K+ channels Classification by selectivity Na+ channels Ca2+ channels Transient receptor potential (TRP) channels K+ channels Cyclic nucleotide-gated channels H+ channels Ligand-gated channels Ionotropic receptors ATP-sensitive channels Cl- channels Anion channels Cation channels Cyclic nucleotide-gated channels Inward rectifiers Light-gated channels Mechanosensitive channels Gap junctions Ligand-gated ion channels Cys-loop receptors GABAA receptors Anion selective Glycin receptors nACh receptors Serotonin Receptors Ionotropic glutamate receptors Hyperpolarization activated cyclic nucleotide-gated channels ATP-sensitive potassium channels Cation selective Ligand-gated ion channels → Cys-loop receptors → general structure Ligand-gated ion channels → Cys-loop receptors → general structure 5-fold rotational symmetry Ligand-gated ion channels → Cys-loop receptors → Ligand-gated ion channels – Cys-loop receptors General structure Extracellular General structure –→ Extracellular domaindomain Ligand binding site Allosteric modulator binding site Ligand binding site Ligand-gated ion channels → Cys-loop receptors → Ligand-gated ion channels – Cys-loop receptors General structure Extracellular General structure –→ Extracellular domaindomain • the „binding pocket” is formed by one principal and one complementary subunit • Binding pocket residues: • A, B, C loops from the principal subunit • D, E, F β-sheets from the complementary subunit • 2 bindings sites are required for channel activation • ECD contracts around agonists, relaxes around antagonists • cation-π interactions Ligand-gated ion channels → Cys-loop receptors → General structure → Transmembrane domain M1: may be involved in transmitting movements from ligand-bound ECD to M2 M2-M3 loop: critical role in transmitting the energy of binding into channel opening M2: provides pore-lining residues, constitutes the gate M3 and M4: shield M2 from the lipid environment Ligand-gated ion channels → Cys-loop receptors → General structure → Transmembrane domain Hydrophobic girdle Ion selectivity filter hydrophobic charged Anionic channels (GABAA, Gly-R) Cationic channels (nACh-R, 5-HT-R ) -1` position: Glutamic acid -1` position: uncharged Ligand-gated ion channels → Cys-loop receptors → GABAA receptors → Subunits Class IUPHAR protein name Gene α1 GABRA1 α2 GABRA2 α3 GABRA3 α4 GABRA4 α5 GABRA5 α6 GABRA6 β1 GABRB1 β2 GABRB2 β3 GABRB3 γ1 GABRG1 γ2 GABRG2 γ3 GABRG3 delta δ GABRD epsilon ε GABRE pi π GABRP theta θ GABRQ ρ1 GABRR1 ρ2 GABRR2 ρ3 GABRR3 alpha beta gamma rho GABA is the most common neurotransmitter in the CNS GABAA receptors found in 40% of synapses in the brain GABA-R classes: GABAA: ionotropic GABAB: G-protein-coupled There are 19 different GABA-R receptor subunits Most abundant subunit classes: alpha, beta, gamma, delta (rho is expressed in the retina) GABAA is anion selective Ligand-gated ion channels → Cys-loop receptors → GABAA receptors → Subunit stoichiometry two different α and two different β subunits can be present ϒ cannot be precipitated with other ϒsubunits δ is not present with ϒ 2 α, 2 β and 1 ϒ or δ subunits make up the channel estimated number of different subtypes: 800 •α1 - β2 - ϒ2 is the most common composition α2βγ2, α3βγ2, α4βγ2, α5βγ2, α6βγ2, α4βδ and α6βδ are also common to lower extent a Ligand-gated ion channels → Cys-loop receptors → GABAA receptors → Allosteric modulaMon BZ1 class: contain the α1 subunit cortex, talamus, cerebellum sedative, amnesia BZ2 class: contain the α2 subunit limbic system, motor neurons anxiolytic, myorelaxant Ligand-gated ion channels → Cys-loop receptors → Glycine receptors Gly is one of the most common neurotransmitter in the CNS Gly-R is anion selective 5 known subunits: α 1 – 4 and β Developmental switch of isoforms: fetal form α2 homomers adult form: α1β heteromers Subunit stoichiometry: 3α:2β long-held dogma, no evidence Ligand-gated ion channels → Cys-loop receptors → Nicotinic Acetylcholine Receptors Cys-loop receptor signature structure Ligand-gated ion channels → Cys-loop receptors → Nicotinic Acetylcholine Receptors nACh-R is a cation channel 17 known subunits: α 1 – 10 β1 – 5 δ ϒ ε Na+ (inward) and K+ (outward) ions flow through the open channel, net current is inward (depolarizing) Muscle type nAChR (neuromuscular junction): α1, β1, γ, and δ – embryonic α1, β1, δ, and ε - adult 2:1:1:1 ratio Neural type nAChR (central or peripheral nervous system): homo- or heteromeric combinations of α2−α10 and β2−β4 subunits e.g. (α4)3(β2)2, (α4)2(β2)3, (α7)5 Ligand-gated ion channels → Cys-loop receptors → Ionotropic Serotonin Receptors Serotonin: 5-hydroxitryptamine 5-HT receptors Family Type Mechanism 5-HT1 Gi/Go-protein coupled. Decreasing cellular levels of cAMP. 5-HT2 Gq/G11-protein coupled. Increasing cellular levels of IP3 and DAG. 5-HT3 Ligand-gated Na+ and K+ cation channel. Depolarizing plasma membrane. 5-HT4 Gs-protein coupled. Increasing cellular levels of cAMP. 5-HT5 Gi/Go-protein coupled. Decreasing cellular levels of cAMP. 5-HT6 Gs-protein coupled. Increasing cellular levels of cAMP. 5-HT7 Gs-protein coupled. Increasing cellular levels of cAMP. 5 genes encoding for 5 subunits HTR3A 5-HT3A HTR3B 5-HT3B HTR3C 5-HT3C HTR3D 5-HT3D HTR3E 5-HT3E Potential Inhibitory Excitatory Excitatory Excitatory Inhibitory Excitatory Excitatory Ligand-gated ion channels → Glutamate Receptors (no Cys-loops here) Nervous system: Glutamate is the main excitatory neurotransmitter, present in 50% of nervous tissue Glutamic Acid Taste buds: GluR is responsible for the transmission of the umami taste stimuli Clinical conditions: Autism Attention Deficit Hyperactivity Disorder (ADHD) Diabetes Multiple sclerosis Schizophrenia etc. Ligand-gated ion channels → Glutamate Receptors Ionotropic Metabotropic AMPA receptors Kainate receptors NMDA receptors GluA1-4 GluK1-5 GluN 9 isoforms Homo- or heteromers GluK1-3: homo- or heteromers (GluN1)2 + (GluN2)2 or GluN1 + GluN2 GluK4-5: “silent subunits” Four subunits assemble in one channel mGluR Ligand-gated ion channels → Glutamate Receptors ATD: amino-terminal domain LBD: ligand binding domain TMD: transmembrane domain CTD: carboxy-terminal domain Ligand-gated ion channels → Glutamate Receptors Tetrameric structure Ligand-gated ion channels → Glutamate Receptors Dimer of dimers! Same polypeptide Different conformations! Ligand-gated ion channels → Glutamate Receptors Ligand-gated ion channels → Glutamate Receptors Ligand binding-induced conformation changes Voltage-gated ion channels → General membrane topology Inward rectifiers Tetrameric structure Membrane topology of one subunit Inward rectifiers 2 1 3 0 AP 4 4 Is it an inward current? IK1 “Linear” current-voltage relationship Blockade by cytoplasmic Mg2+ and polyamines Inward rectifiers and voltage-gated channels → Ion selectivity Conserved selectivity filter motif Voltage-gated ion channels → General membrane topology Voltage-gated ion channels → Conformation transitions Closed Open Closed Open Inactivated N-type inactivation C-type inactivation Voltage-gated ion channels → Conformation transitions → Various kinetics contributes to functional diversity Six TMD structure Transient outward current Delayed rectifier current 2 2 1 1 3 3 0 0 4 mV 5050mV -35mV mV -35 -80mV mV -80 4 4 50mV -40mV 4 Voltage-gated ion channels → Auxiliary subunits The minK story The cardiac delayed rectifier KvLQT1 drives no current in homomeric form A single TMD protein called minK was injected into Xenopus oocytes → huge delayed rectifier potassium current is generated. How is that possible? Voltage-gated ion channels → Auxiliary subunits Molecular toolkit: the KCNE gene family KCNE genes KCNE1 - minK KCNE2 – MiRP1 KCNE3 – MiRP2 KCNE4 – MiRP3 KCNE5 – MiRP4 Voltage-gated ion channels → Auxiliary subunits Molecular toolkit: the KCNE gene family KvLQT1 + minK KvLQT1 + MiRP2 KvLQT1 + MiRP4 Voltage-gated ion channels → Diversity of potassium channels Voltage-gated ion channels → Sodium channels “Tetramer”-mimicking structure 2 1 3 0 4 4 All encoded by a single giant polypeptide Voltage-gated ion channels → Calcium channels α2δ subunit β subunit Increased traficking Increase current amplitude Left-shifted voltage dependence of activation Faster activation and inactivation Left-shifted voltage dependence of inactivation