Scyllatoxin is a toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

, from the scorpion

Scorpion

Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

 Leiurus quinquestriatus hebraeus

Deathstalker

The deathstalker , is a species of scorpion, a member of the Buthidae family. It is also known as Palestine yellow scorpion, Omdurman scorpion, Israeli desert scorpion and numerous other colloquial names, which generally originate from the commercial captive trade of the animal...

, which blocks small-conductance Ca²⁺-activated K⁺ channels.

Source

Scyllatoxin is one of the components of the venom

Venom

Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

 of the Israeli scorpion

Scorpion

Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

 ‘Leiurus quinquestriatus hebraeus’. It consists of only 0.02% of the total protein in crude venom.

Chemistry

Leiurotoxin I is a 31-residue peptide, with a helix

Helix

A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

 and a short antiparallel

Antiparallel (biochemistry)

In biochemistry, two molecules are antiparallel if they run side-by-side in opposite directions or when both strands are complimentary to each other....

 β-sheet. This toxin is stabilized by disulfide bonds: Cys8-Cys26 and Cys12-Cys28 is bound to the β-sheet, Cys3-Cys21 is bound to an N-terminal segment preceding the helix. Leiurotoxin adopts the ά/β motif. Especially the positively charged residues (Arg6 and Arg13, which are located in the ά helix) are important for the expression of toxin biological activities and for its receptor affinity.

Target

Scyllatoxin is a blocker of small-conductance Ca²⁺– activated K⁺ channels at 10-13–10-11 M concentrations in various cell types.
This toxin shows similarity in its physiological activity and binding specificity to apamin

Apamin

Apamin is an 18 amino acid peptide neurotoxin found in apitoxin . It selectively blocks SK channels, a type of Ca2+-activated K+ channel expressed in the central nervous system and smooth muscle...

, but both toxins show no structural similarity.

Mode of action

Scyllatoxin blocks the slow after-hyperpolarization

Hyperpolarization

Hyperpolarization has several meanings:* Hyperpolarization occurs when the strength of the electric field across the width of a cell membrane increases...

 that follows an action potential

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

 in some nerve cells.

Toxicity

Scyllatoxin induces spontaneous contractions in guinea pig

Guinea pig

The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...

taenia coli muscle cells that have
been relaxed with epinephrine.