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Tityustoxin-15 (Ts15 or Potassium channel toxin α-KTx 21.1), which is produced by the Tityus serrulatus (Brazilian scorpion), targets the voltage-gated potassium channels, primarily the subtypes Kv1.2 and Kv1.3. Ts15 is the first member of the new subfamily α-Ktx 21.

Etymology
The full name of the toxin is: Potassium channel toxin α-KTx 21.1. The name refers to its effects on voltage-gated potassium channels (Kv channels) and indicates that it’s the first member of the α-scorpion toxin subfamily 21.

Source
Ts15 can be isolated from the venom of the Tityus serrulatus, otherwise known as the Brazilian yellow scorpion. This toxin is the most deadly scorpion toxin in Brazil, with a lethality rate of 0.15%. Ts15 is only one of many neurotoxins that can be found in the venom of the Tityus serrulatus.

Chemistry
Ts15 is a peptide with a sequence length of 36 amino acids, which are crosslinked by three disulfide bridges. The 27th position in the amino acid sequence undergoes N-linked glycosylation. Ts15 is a scorpion short toxin. The rest of the structure of the toxin remains unknown, because its structure is quite unique. Therefore, it cannot easily be compared to other members of the α-family, since the structural similarities between Ts15 and the other α-families are less than 30%.

Target
Kv channels are the main targets of Ts15. While other members of the α-family generally target both Kv channels and sodium channels (Nav channels), Ts15 only targets Kv channels. Ts15 mainly targets Kv1.2 and Kv1.3: it blocks the channel’s current by 73% and 50% respectively. When all targeted channels are compared, Ts15 has the highest affinity for Kv1.2 channels. Besides these channels, Ts15 also targets Shaker IR channels, Kv1.6 channels and the  Kv2.1 channels. The effects of Ts15 are voltage-independent, meaning it can bind to a channel in any state of activation, and they also are reversible. The precise mode of action is currently unknown.

Toxicity
The LD50 of Ts15 is unknown. The symptoms caused solely by Ts15 have not been studied extensively. However, Ts15 is known to block the Kv1.3 channels on autoreactive effector memory T-cells. The binding of the toxin triggers immunosuppression, by decreasing the calcium influx into the cell.

Treatment
In general, the venom of the Tityus serrulatus is treated with scorpion antivenom serum, named Soro antiscorpionico. A human antibody fragment, serrumab, neutralises most of the venom. However, this antibody works on the entire venomous cocktail of the scorpion. Information about treating Ts15 alone is currently unavailable.