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Home , Agitoxin, Batrachotoxin, Conotoxin, Dendrotoxin, Kaliotoxin, Margatoxin

ZOO4670/5670 Lecture No. 6

Neurotoxins as Tools for Studying Channel Structure and Functions

Qian-Quan Sun Ph.D (@uwyo.edu)

Univ. Wyoming

Today’s outline

• 1. Basics about channel block • 2. and channels • 3. Sodium channels: toxins and local • 4. Sea snails, and channels

1 Honey bee Blocks Ca2+ activated potassium channels

Honey bee

Stichodactyla Blocks voltage-gated potassium channels

sea anemone

2 3 Palytoxin Soft coral Activates sodium channels

Capsaicin Cayenne Pepper Excites peripheral nerve endings

4 Arrow Prevents sodium channels from closing

Blue-Ringed Maculotoxin Blocks sodium channels

5 Model or State 1 State 2 all molecules scheme begin here at t= 0 k21 normal function closed open

units: s-1 units: M-1s-1

+ k23 = k [Drug] k 21 drug simple block closed open blocked

current time constant time constant = 1/k21 = 1/(k21+ k23) none

Ligand binding and dose response curve Concentration of toxin (nM)

6 use-dependent block= open

inside

“Trapped” or Functioning channel “Use-Dependent” Blocker

Antiarrhythmics () Antiepileptics / (brain) “use-dependent blocker” “use-dependent blocker” example: () ( = Dilantin® )

A use-dependent blocker

stimuli

impulses fail impulses (voltage)

channel population threshold (currents) pronounced block little block at brief intervals at long intervals

7 Green snake

Pore region sequence of ShaKv1.1.

The surface of ShaKv1.1.

KcsA

The surface color represents the change in binding energy of dendrotoxin associated with

8 Conclusions: dendrotoxin binds near the pore entryway but does not act as a physical plug.

Hypothetical binding orientation for dendrotoxin

Scorpion toxin fits even better to the pore entryway!

Binding orientation of toxin on the K. channel.

9 C11H17N3O8

alpha-scorpion toxin beta-scorpion toxins Sea anemone

Motif III

b-scorpion toxins trap Kd =0.1nM IIS4 in the outward, activated position. Channel must be activated for toxin effect. a-scorpion toxin trap IVS4 in an inward, partially activated position. Motif I Prolonged depolarization drives the toxins off their Motif IV receptor site

10 that block Na+ channels

Local Anesthetics Antiarrhythmic Drugs Lidocaine Many others

Anticonvulsants Phenytoin

use dependent block

11 Baldomero “Toto” Olivera Ph D [email protected] Distinguished Professor Olivera lab directory

Geographer’s cone Magician’s cone

Leopard cone Cloth-of-gold cone

12 A : 27 amino acids held together by bonds individual specifically block individual ion channels.

13 The lethal sea snail toxin is a promising killer .

Ziconotide is the synthetic equivalent of a 25-amino-acid, polybasic from the of , 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 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 ziconotide appeared and diminished rapidly in plasma and resulted in relatively little plasma binding. Intravenous ziconotide degraded in brain tissue in 2 to 24 hours, produced no detectable intermediates, and was cleared quickly from both (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.

14 Cerebral cortex (layer II/III)

Thalamus

Trigeminal nucleus

15 Voodoo • Ancient haitian traditions used the puffer for its voodoo practices. – The tetrodotoxin is used to create – 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.

Toxins that act on voltage-gated ion channels

Name Source Neuronal Action Funnel Web Blocks calcium channels Scorpion Blocks potassium channels Apamin Honey bee Blocks potassium channels Blue Mountains Atracotoxin Funnel Web Blocks voltage-gated calcium channels Spider Poison Arrow Batrachotoxin Prevents sodium channels from closing Frog Cayenne Pepper Excites peripheral nerve endings Scorpion Blocks potassium channels Opens sodium channels Conotoxin Marine Snail voltage-sensitive calcium channels; sodium channels Dendrotoxin Green Mamba Blocks voltage-gated potassium channels South American Grammotoxin Rose Blocks calcium channels SIA Tarantula Dinoflagellate Blocks sodium channels Scorpion Blocks potassium channels Scorpion Blocks potassium channels South African Kurtoxin Blocks calcium channels Scorpion

16 Toxins that act on voltage-gated ion channels: continued

Blue-Ringed Maculotoxin Blocks sodium channels Octopus Scorpion Blocks potassium channels Scorpion Blocks sodium channels Palytoxin Soft coral Activates sodium channels Phoneutriatoxin Banana spider Slows inactivation Chilean fire Phrixotoxin Blocks potassium channels tarantula Funnel web Robustotoxin Opens sodium channels spider Dinoflagellate Blocks sodium channels SNX-482 African Tarantula Blocks calcium channels Stichodactyla Blocks voltage-gated potassium Sea Anemone Toxin channels Australian Taipan Inhibits voltage-gated calcium channels snake Tetrodotoxin Pufferfish Blocks sodium channels (TTX) Brazilian Tityustoxin-K Blocks potassium channels Scorpion Funnel web Versutoxin Opens sodium channels spider

17