Makatoxin-3

Key takeaways

Makatoxin-3 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Makatoxin-3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Makatoxin-3 from memory before moving on to harder problems.

Reference excerpt

Makatoxin-3 (a.k.a. MkTx-3, MKTX III or Makatx III) is an α-like scorpion neurotoxin found in the venom of Olivierus martensii. Makatoxin-3 both enhances the activation and slows down the inactivation of voltage-gated NaV1.7 channels, resulting in hyperexcitability of the neurons involved in pain perception.

Source Makatoxin-3 is a neurotoxin that can be found in the venom of the scorpion Olivierus martensii, also known as Buthus martensii Karsch (BmK) or the Chinese Scorpion. This scorpion is also commonly known as the Chinese scorpion, as it is widely found in China, as well as Korea and Mongolia. Makatoxins account for approximately 4% of the total BmK venom protein. After high temperature processing of the venom, Makatoxins make up 0.8% of the total protein.

Chemistry Makatoxin-3 is made up of 85 amino acid residues, 19 of which make up the signal peptide at the N-terminal, and four disulfide bonds. It has a high sequence homology (90% identity) with two other toxins from the same Makatoxin protein family, Makatoxin-1 and Makatoxin-2.

The full amino acid sequence of Makatoxin-3 is the following (with the mature peptide underlined): MNYLI VISFA LLLMT GVESG RDAYI AKKEN CTYFC ALNPY CNDLC TKNGA KSGYC QWAGR YGNAC WCIDL PDKVP IRIPG PCIGR For comparison, the amino acid sequence of Mktx-2 is (again with the mature peptide underlined): MNYLI VISFA LLLMT SVESG RDAYI ADSEN CTYFC GSNPY CNDLC TENGA KSGYC QWAGR YGNAC WCIDL PDKVP IRIPG PCRGR Two key residues of Makatoxin-3 have been identified: K9 and R58. Their substitutions K9D and R58A in mutated Makatoxin-3 reduce the efficacy of the toxin to cause pain in mice. Makatoxin-3 is thermostable, as processing it by high temperature (60 °C) does not affect the bioactivity of Makatoxin-3 despite the protein concentration going down by 50%. Makatoxin-3 is also stable in artificial gastric juice, but not in artificial intestinal juice, so Makatoxin-3 may be protected from enzymatic digestion.

Target and Mode of Action Makatoxin-3 is an α-toxin that binds to the S3-S4 loops of the voltage sensor domain IV (VSD4) of NaV1.7 in dorsal root ganglion (DRG) neurons. It is a NaV1.7 agonist. Makatoxin-3 has little to no effect on NaV1.1, NaV1.3, NaV1.6, NaV1.8, and NaV1.9 channels. Makatoxin-3 shows dose-dependent effects on both the activation and the inactivation of NaV1.7. The toxin slows the inactivation kinetics of NaV1.7 currents. The average persistent currents are larger at both low (250 nmol/kg) and high (750 nmol/kg) concentrations due to the incomplete NaV1.7 channel inactivation at depolarized potentials (-45 mV and higher). At high concentration (750 nmol/kg), the curve of the peak current shifts to the left of the hyperpolarization direction, reaching the peak earlier than in the absence of the toxin; the action potential is also prolonged by shifting the steady-state fast inactivation current to hyperpolarization potentials by -9.3 mV. Furthermore, at high concentration (750 nmol/kg), Makatoxin-3 causes NaV1.7 to open at hyperpolarized potential by shifting its voltage-dependent activation curve by -8.6 mV.

Toxicity Makatoxin-3 evokes pain and allodynia. After injecting 25 nmol/kg, 50 nmol/kg, and 150 nmol/kg of Makatoxin-3 respectively, mice exhibit flinching behavior due to the pain-inducing effect for approximately 30 minutes before diminishing in a dose-dependent manner (the higher the dose, the higher the number of flinches).

Therapeutic use Interestingly, notwithstanding the pain response induced by the toxin, Makatoxin-3 also shows an analgesic effect in a dose-dependent manner (50 nmol/kg, 150 nmol/kg, and 450 nmol/kg). 450 nmol/kg elicits an 80% reduction of paw-flinch pain behavior in mice when they are intraperitoneally injected with another pain-inducing substance 30 minutes after the Makatoxin-3 injection. However, if the scorpion body is processed by high temperature, it requires an even higher concentration of Makatoxin-3 to elicit the analgesic effect due to the loss of these peptides. A mutant variant of the neurotoxin, Makatoxin-3-R58A, still produces the analgesic effect, but largely loses its pain-inducing effect. Unlike morphine, which is a strong opioid receptor analgesic with the addictive side effect, the analgesic activity induced by Makatoxin-3 cannot be reversed by naloxone (μ-opioid receptor antagonist). This means that Makatoxin-3 has an analgesic effect that is not dependent on the endogenous opioid system. Therefore, Makatoxin-3 is being studied as a new potential painkiller.

References

External links Chemistry details:

P56569 · MKTX1_MESMA Q86BW9 · MKTX2_MESMA P59853 · MKTX3_MESMA

Illustrations

Worked examples

Example 1 — a first encounter with Makatoxin-3

Start with the simplest possible case. Write down what Makatoxin-3 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 Makatoxin-3 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 Makatoxin-3 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 Makatoxin-3

In research: Makatoxin-3 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 Makatoxin-3 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: Makatoxin-3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ion channel toxins, Neurotoxins, Scorpion toxins, so understanding it makes those chapters shorter.
In everyday life: Look for Makatoxin-3 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 Makatoxin-3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Makatoxin-3 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 Makatoxin-3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Makatoxin-3 in simple terms?

Makatoxin-3 (a.k.a. MkTx-3, MKTX III or Makatx III) is an α-like scorpion neurotoxin found in the venom of Olivierus martensii.

Why does Makatoxin-3 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 Makatoxin-3?

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 Makatoxin-3.