Univ. Wyoming · Batrachotoxin Poison Arrow Frog Prevents sodium channels from closing Maculotoxin...
Transcript of Univ. Wyoming · Batrachotoxin Poison Arrow Frog Prevents sodium channels from closing Maculotoxin...
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ZOO4670/5670 Lecture No. 6
Neurotoxins as Tools for Studying Ion Channel Structure and Functions
Qian-Quan Sun Ph.D ([email protected])
Univ. Wyoming
Today’s outline
• 1. Basics about channel block• 2. Snake toxins and potassium channels• 3. Sodium channels: toxins and local
anesthetics• 4. Sea snails, spiders and calcium
channels
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Honey bee
Apamin Honey bee Blocks Ca2+ activated potassium channels
Stichodactyla Toxin Sea Anemone Blocks voltage-gated potassium channels
sea anemone
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Palytoxin Soft coral Activates sodium channels
Capsaicin Cayenne Pepper Excites peripheral nerve endings
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Batrachotoxin Poison Arrow Frog Prevents sodium channels from closing
Maculotoxin Blue-Ringed Octopus Blocks sodium channels
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closed open
State 1 State 2
normal functionk21
all molecules begin here at
t= 0
Model orscheme
closed opendrug
blockedsimple block
k21
k23 = k+[Drug]
units: s-1 units: M-1s-1
time constant= 1/k21
current
none
time constant= 1/(k21+ k23)
Ligand binding and dose response curveConcentration of toxin (nM)
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Functioning channel“Trapped” or
“Use-Dependent” Blocker
inside
use-dependent block= open channel blocker
Antiarrhythmics (heart) “use-dependent blocker”example: (procainamide)
Antiepileptics / anticonvulsants (brain) “use-dependent blocker”(phenytoin = Dilantin® )
pronounced blockat brief intervals
little blockat long intervals
impulses(voltage)
channelpopulation(currents)
stimuli
impulses fail
A use-dependent blocker
threshold
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Green mamba snake
The dendrotoxin receptor surface of ShaKv1.1.
Pore region sequence of ShaKv1.1.
KcsA
The surface color represents the change in binding energy of dendrotoxin associated with mutation
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Conclusions: dendrotoxin binds near the pore entryway but does not act as a physical plug.
Hypothetical binding orientation for dendrotoxin
Binding orientation of scorpion toxin on the K. channel.
Scorpion toxin fits even better to the pore entryway!
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TetrodotoxinC11H17N3O8
Motif IV
Motif I
Motif III
beta-scorpion toxins
b-scorpion toxins trap IIS4 in the outward, activated position.Channel must be activated for toxin effect.
alpha-scorpion toxinSea anemone
a-scorpion toxin trap IVS4 in an inward, partially activated position. Prolonged depolarization drives the toxins off their receptor site
Kd =0.1nM
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Neurotoxins that block Na+ channels
AntiarrhythmicDrugs
LidocaineMexiletineQuinidineFlecainide
AnticonvulsantsPhenytoin
CarbamazepineLamotrigine
Local AnestheticsEtidocaineLidocaine
Many others
use dependent block
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Baldomero “Toto” Olivera Ph D [email protected] ProfessorOlivera lab directory
Magician’s coneGeographer’s cone
Leopard cone Cloth-of-gold cone
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A conotoxin:27 amino acidsheld together by disulfide bondsindividual conotoxins specifically block individual ion channels.
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The lethal sea snail toxin is a promising pain killer .
Ziconotide is the synthetic equivalent of a 25-amino-acid, polybasic peptide from the venom of Conusmagus, a marine snail. It is the first selective N-type, voltage-sensitive calcium-channel blocking agent to reach clinical trials.In the current study, patients aged 24 to 85 years with refractory pain from advanced cancer or AIDS were randomized to ziconotide or placebo in a 2:1 ratio. Intrathecal ziconotide was titrated over 5 to 6 days, followed by a 5-day maintenance phase. Mean pain scores improved 52.9% in the ziconotide group, compared with 17.5% in the placebo group, with no reduction in efficacy during the maintenance phase. Five patients receiving ziconotide achieved complete pain relief.Ziconotide also seems to improve the sleep pattern in some patients with chronic severe pain. Patients experienced positive effects on nocturnal sleep duration and believed that remaining pain symptoms interfered less with their daily life.In experimental studies of absorption, distribution, metabolism, and elimination, intrathecal ziconotideappeared and diminished rapidly in plasma and resulted in relatively little plasma protein binding. Intravenous ziconotide degraded in animal brain tissue in 2 to 24 hours, produced no detectable intermediates, and was cleared quickly from both cerebrospinal fluid (CSF) and the circulatory system. This accelerated clearance rate likely means that the distribution of ziconotide throughout CSF and metabolism within CSF are also rapid.
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Trigeminal nucleus
Cerebral cortex (layer II/III)
Thalamus
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Voodoo• Ancient haitian traditions used the puffer fish for its voodoo
practices. – The tetrodotoxin is used to create zombies– It puts the people in a death-like state
• The towns people would take some to be put into this state
– While under this state, they would be forced to do odd jobs.- The zombies were used as a social damper to scare towns people to keep them in line.
Name Source Neuronal Action
Agatoxin Funnel Web Spider Blocks calcium channels
Agitoxin Scorpion Blocks potassium channels
Apamin Honey bee Blocks potassium channels
AtracotoxinBlue Mountains
Funnel Web Spider
Blocks voltage-gated calcium channels
Batrachotoxin Poison Arrow Frog Prevents sodium channels from closing
Capsaicin Cayenne Pepper Excites peripheral nerve endings
Charybdotoxin Scorpion Blocks potassium channels
Ciguatoxin Dinoflagellate Opens sodium channels
Conotoxin Marine Snail voltage-sensitive calcium channels; sodium channels
Dendrotoxin Green Mamba Blocks voltage-gated potassium channels
GrammotoxinSIA
South American Rose Tarantula
Blocks calcium channels
Gonyautoxin Dinoflagellate Blocks sodium channels
Iberiotoxin Scorpion Blocks potassium channels
Kaliotoxin Scorpion Blocks potassium channels
Kurtoxin South African Scorpion Blocks calcium channels
Toxins that act on voltage-gated ion channels
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Maculotoxin Blue-Ringed Octopus Blocks sodium channels
Margatoxin Scorpion Blocks potassium channels
Noxiustoxin Scorpion Blocks sodium channels
Palytoxin Soft coral Activates sodium channels
Phoneutriatoxin Banana spider Slows sodium channel inactivation
Phrixotoxin Chilean fire tarantula Blocks potassium channels
Robustotoxin Funnel web spider Opens sodium channels
Saxitoxin Dinoflagellate Blocks sodium channels
SNX-482 African Tarantula Blocks calcium channels
StichodactylaToxin Sea Anemone Blocks voltage-gated potassium
channels
Taicatoxin Australian Taipansnake Inhibits voltage-gated calcium channels
Tetrodotoxin(TTX) Pufferfish Blocks sodium channels
Tityustoxin-K Brazilian Scorpion Blocks potassium channels
Versutoxin Funnel web spider Opens sodium channels
Toxins that act on voltage-gated ion channels: continued