Jingzhaotoxin

Key takeaways

Jingzhaotoxin belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Jingzhaotoxin to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Jingzhaotoxin from memory before moving on to harder problems.

Reference excerpt

Jingzhaotoxin proteins are part of a venom secreted by Chilobrachys jingzhao, the Chinese tarantula. and act as neurotoxins. There are several subtypes of jingzhaotoxin, which differ in terms of channel selectivity and modification characteristics. All subspecies act as gating modifiers of sodium channels and/or, to a lesser extent, potassium channels.

Sources Chilobrachys jingzhao, also known as the Chinese earth tiger tarantula or Chilobrachys guangxiensis, can be found in China and Asia. This large tarantula belongs to the family of Theraphosidae.

Chemistry Jingzhaotoxins reported on this page are 29-36-residue polypeptides with varying numbers of stabilizing disulfide bridges.

Target

Jingzhaotoxins can target multiple channels. The following IC50 values have been determined:

'*' Only a dissociation constant (Kd) was measured. Kd; 0.43 μM '**' Only a Kd was measured. Kd; 1.28 μM '***' Only a Kd was measured. Kd; 0.74 μM

Mode of action

JZTX-I Effect on voltage-gated sodium channels (VGSC) JZTX-I preferentially acts on cardiac sodium channels, but also affects tetrodotoxin-sensitive (TTX-S) voltage-gated sodium channels (VGSC) in dorsal root ganglion (DRG) neurons. It modifies the sodium current by inhibiting channel inactivation and speeding up recovery after inactivation. JZTX-I does not affect the activation threshold of sodium channels. Effect on potassium channels JZTX-I has a modest effect on potassium currents by slowing the rate of activation of Kv2.1 and Kv4.1 channels and increasing the tail current deactivation.

JZTX-II Effect on VGSC JZTX-II has high affinity to the tetrodotoxin-resistant (TTX-R) VGSC in cardiac myocytes where it significantly slows rapid inactivation. Although JZTX-II does not have an effect on TTX-R neuronal channels in DRG neurons it does affect TTX-S sodium currents by slowing down their inactivation. Effect on potassium channels At this point, the effects of JZTX-II on potassium channels are unknown.

JZTX-III Effect on VGSC JZTX-III has a high affinity to the TTX-R Nav1.5 voltage gated sodium channel which is expressed in cardiac myocytes but not in neurons. It modifies the sodium channel current by shifting its activation curve to a more depolarized voltage without affecting its inactivation curve. JZTX-II is docked to the Nav1.5 DIIS3-4 linker, which is responsible for its high selectivity. Effect on potassium channels JZTX-III modifies the voltage gated Kv2.1 potassium channel in cardiac myocytes and can bind to both open and closed channels. It modifies the gating of Kv2.1 channel by shifting the activation curve to a more depolarized voltage and by speeding up deactivation.

JZTX-IV Effect on VGSC JZTX-IV acts on TTX-S sodium channels in DRG neurons by weakly reducing peak amplitudes and by obviously slowing inactivation kinetics. In contrast, JZTX-IV acts on TTX-R sodium channels on cardiac myocytes by obviously reducing its peak current and by weakly slowing inactivation kinetics. Additionally, JZTX-IV shifts the steady-state inactivation curve on both receptors. Even at high concentrations, JZTX-IV does not have any effect on TTX-R sodium channels on rat DRG neurons or on TTX-S sodium channels on hippocampal neurons. Effect on potassium channels At this point, the effects of JZTX-IV on potassium channels are largely unknown.

JZTX-V Effect on VGSC JZTX-V has a high affinity to the resting closed state of TTX-R (Nav1.8 Nav1.9) and TTX-S (Nav1.6, Nav1.7) VGSC in DRG neurons. It modifies the sodium channel current by shifting its activation curve to a more depolarized voltage and its inactivation curve to a more hyperpolarized voltage. This means that the toxin-bound sodium channel will open at a more positive membrane potential and closes at a more negative membrane potential. Effect on potassium channels JZTX-V mainly affects the Kv4.2 potassium channel current by shifting its activation curve to a more depolarized direction and, at high concentrations, by speeding up deactivation.

JZTX-IX Effect on VGSC JZTX-IX act on both TTX-R and TTX-S channels by shifting their activation state to a more depolarized voltage. In addition it captures the sodium channels at a closed state which speeds up inactivation. Effect on potassium channels JZTX-IX affects only the Kv2.1 channel by shifting its activation curve to a more depolarized voltage.

JZTX-XI Effect on VGSC JZTX-XI reduces the peak sodium current amplitude of sodium channels expressed in cardiac myocytes and slows down current inactivation. JZTX-XI shows no effects on both TTX-R and TTX-S sodium currents in dorsal root ganglion neurons Effect on potassium channels JZTX-XI shifts the activation curve of Kv2.1 to a more depolarized voltage and speeds up its deactivation.

JZTX-XII Effect on VGSC At this point, the effects of JZTX-XII on sodium channels are largely unknown. Effect on potassium channels JZTX-XII specifically acts on Kv4.1 potassium channels. It modulates potassium current by shifting Kv4.1 activation to more depolarized voltages and by producing a concentration-dependent slowing of activation and inactivation kinetics.

JZTX-34 Effect on VGSC JZTX-34 inhibits TTX-S sodium currents, but has no effect on TTX-R sodium currents. JZTX-34 does not affect activation/inactivation kinetics nor does it affect recovery rate from inactivation. Effect on potassium channels At this point, the effects of JZTX-34 on potassium channels are largely unknown.

Toxicity The crude venom of Chilobrachys jingzhao is lethal to mice with an intraperitoneal LD50 of 4.4 mg/kg. The scarce LD50 values that have been described for the toxins that make up the venom vary; 0.23 mg/kg (JZTX-IX) – 1.48 mg/kg (JZTX-I).

Worked examples

Example 1 — a first encounter with Jingzhaotoxin

Start with the simplest possible case. Write down what Jingzhaotoxin claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Jingzhaotoxin before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Jingzhaotoxin ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Jingzhaotoxin

In research: Jingzhaotoxin appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Jingzhaotoxin in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Jingzhaotoxin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ion channel toxins, Neurotoxins, Spider toxins, so understanding it makes those chapters shorter.
In everyday life: Look for Jingzhaotoxin outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Jingzhaotoxin in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Jingzhaotoxin means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Jingzhaotoxin out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Jingzhaotoxin in simple terms?

Jingzhaotoxin proteins are part of a venom secreted by Chilobrachys jingzhao, the Chinese tarantula. and act as neurotoxins. There are several subtypes of jingzhaotoxin, which differ in terms of channel selectivity and modification characteristics.

Why does Jingzhaotoxin matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Jingzhaotoxin?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Jingzhaotoxin.