Kappa- Hefutoxin 1 and 2 are toxin

Toxin

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

s from 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 Asian forest black 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...

 with a unique structure. It blocks the potassium channel

Potassium channel

In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms. They form potassium-selective pores that span cell membranes...

s Kv1.2 and Kv1.3 and slows the activation of Kv1.3.

Source

The kappa- Hefutoxin 1 and 2 (κ- Hefutoxin1/2) are the toxic components of the venom of the scorpion called Heterometrus fulvipes that belongs to the family scorpionidae. It is also known as the Asian Forest Black Scorpion and is distributed in South India, Indonesia and Malaysia.

Chemistry

The structure of the toxin is unique because it is made up of two parallel helices

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...

 linked by two disulfide bridges

Disulfide bond

In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry...

 without β- sheets

Beta sheet

The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...

. The κ- Hefutoxin1 consists of 22 residues and one amidated C terminus and is therefore the shortest scorpion toxin reported so far. The κ- Hefutoxin2 is build up of 23 residues with free C-terminus.

Target and mode of action

The toxin blocks the voltage-gated potassium channel Kv1.2 and not only blocks the Kv1.3 channels but also slows down their activation kinetics. The blocking effect is most effective when the K⁺ ions flow inward thus at a negative potential.