Heteropodatoxins are

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

toxins from the venom of the giant crab spider ''

Heteropoda venatoria ''Heteropoda venatoria'' is a species of spider in the family Sparassidae, the huntsman spiders. It is native to the tropical regions of the world, and it is present in some subtropical areas as an introduced species. Its common names include gi ...

'', which block Kv4.2

voltage-gated potassium channel Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized ce ...

Sources

Heteropodatoxins are purified from the venom of the giant crab spider, ''Heteropoda venatoria'' .

Chemistry

Heteropodatoxins contain an Inhibitor Cystine Knot (ICK) motif, which consist of a compact disulfide-bonded core, from which four loops emerge . There are three different heteropodatoxins : * heteropodatoxin-1, also known as Toxin AU3/KJ5 or HpTx1 * heteropodatoxin-2, also known as Toxin KJ6 or HpTx2 * heteropodatoxin-3, also known as Toxin AU5C/KJ7 or HpTx3 These three

toxins A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849–1 ...

are structurally similar peptides of 29-32 amino acids . They show sequence similarity to Hanatoxins, which can be isolated from the venom of the Chilean rose tarantula Grammostola rosea .

Target

Heteropodatoxins block A-type, transient

s. All three toxins have been shown to block the potassium channel Kv4.2 . Recombinant heteropodatoxin-2 blocks the potassium channels Kv4.1, Kv4.2 and Kv4.3, but not Kv1.4, Kv2.1, or Kv3.4 .

Mode of action

Heterpodatoxin-2 most likely acts as a gating modifier of the Kv4.2 channels . It shifts the voltage dependence of the

activation Activation, in chemistry and biology, is the process whereby something is prepared or excited for a subsequent reaction. Chemistry In chemistry, "activation" refers to the reversible transition of a molecule into a nearly identical chemical or ...

and the inactivation of the Kv4.3 potassium channel to more positive values. As a result, in the presence of the toxin this channel has a higher probability of being inactivated and a larger depolarization is needed to open the channel. However, heterpodatoxin-2 did not affect the voltage dependence of the Kv4.1 channel, suggesting that the precise mechanism of block remains to be elucidated and a role as a pore blocker cannot be excluded . The voltage dependence of Kv4.2 block varies among the three different heteropodatoxins. It is less voltage dependent for HpTx1 than for HpTx2 or HpTx3 .

Toxicity

The giant crab spider can cause a locally painful bite.

References

Bibliography

* * *{{cite journal , vauthors=Zarayskiy VV, Balasubramanian G, Bondarenko VE, Morales MJ , title=Heteropoda toxin 2 is a gating modifier toxin specific for voltage-gated K+ channels of the Kv4 family , journal=Toxicon , volume=45 , issue=4 , pages=431–42 , year=2005 , pmid=15733564 , doi=10.1016/j.toxicon.2004.11.015 Ion channel toxins