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Evolutionary History of Ion Channels and Neurotransmitters

Evolutionary History of Ion Channels and Neurotransmitters. Neuro Journal Club, 06.03.08 Peter HANTZ, Arendt Laboratory. Types of Ion Channels. Voltage, and voltage/intracellular ligand-gated ion channles K+ VG: fastly and slowly activated, inward rectifier, leak-channels

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Evolutionary History of Ion Channels and Neurotransmitters

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  1. Evolutionary History of Ion Channels and Neurotransmitters Neuro Journal Club, 06.03.08 Peter HANTZ, Arendt Laboratory

  2. Types of Ion Channels Voltage, and voltage/intracellular ligand-gated ion channles K+ VG: fastly and slowly activated, inward rectifier, leak-channels V/ILG: Ca-activated, ATP-activated, cyclic-nucleotide gated Ca+ VG: High voltage activated, Low voltage activated V/ILG: Ca-activated, IP3 activated Na+, Cl-, H+: mostly VG Stretch-activated ion channels Large-conductance MSc Low-conductance MSc Light-gated ion channels

  3. Types of Ion Channels/Receptors Neurotransmitter systems Ionotropic receptors: (ligand-gated ion channels) Cys-loop receptors "fast activating" Anionic(inhibitory) Gly, GABA Cationic(excitatory) 5HT, Ach (nicotinic) Glutamate Gated Channels Glutamate, agonists: AMPA, NMDA, kainate G-protein coupled (metabotropic) receptors ACh, Glu (AMPA, KAIN, NMDA), GABA, 5-HT, DA, NE, ... Shortcut pathway, Second Messenger Cascade Other neurotransmitter receptors peptides, NO, CO

  4. Precursors of the VG-like ion channels small synthetic peptides: -fold into a-helixes -voltage: inserted into membranes -spontaneously build ion 5-7 mer channels 1-TM ion channels: Influenza M2 tetramer 2-TM ion channels: simplest K+ channels: KcsA, Kir (inwardly rectifier) tetramer Present in all three domains of life No voltage-sensitivity

  5. Voltage-sensitive Potassium Channels Gene fusion/duplication: 1.-4. subunits containing six transmembrane crossings S1-S4: voltage gating S4: + charged voltage sensor S5, S6: conserved selectivity filter KvAP

  6. 6TM-type channels Voltage and cyclic nucleotide-gated channels: one-domain, 6TM homotetramers Usual structure of Na and Ca channels: α1 subunits = four LINKED DOMAINS Each: six transmembrane elements

  7. Possible origins of the 6TM channels Two rounds of gene duplications? -Similarities: domains I and III; domains II and IV -Two-domain channels were identified (TPC) They evolved from one-domain 6TM multimers? Ca or Na-channels are more ancestral? 4-domain Ca-channel: already in yeast 4-domain Na-channel: only in multicellular animals not detected in protozoa, in plants But: There is an ancestral bacterial 6TM homotetrameric Na-channel Note: two types of "inactivation" mechanisms (following activation) "ball and chain" or "inactivation loop" Cl channels: conservative, structurally distinct (10-12 domains)

  8. Evolution of the LG-like ion channels Structure (Cys-loop "fast activating" channels): Mostly: pentamers of 1-domain 4-TM proteins N-term extracellular domain: ligand binding site Made of several unrelated proteins? Homologs in bacteria Ancient role: nutrient seeking? osmotic regulation? Now: intercellular communication

  9. Evolution of the LG-like ion channels Ancient: ACh, 5HT and GABA Gly derived from GABA despite Gly is "more simple" Root:?

  10. Structure of the GPCR Single, 7TM polypeptide 2 extracellular loops: transmitter binding site 2 intracellular loops: activate G-proteins Two major groups: PLC-activating (IP3) cAMP decrease Ev. connection between ionotropic (LGICh) and metabotropic (GPCR) receptors ?

  11. Evolution of the GPCR 7-TM architecture in procaryotes: bacteriorhodopsins, no GPC ...linkage to eucaryotic GPCR ? (disputed) GPCR: Present in plants, fungi and animals: common ancestor, 1.2 Gy ago

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