Hemitoxin
Hemitoxin (HTX; α-KTx6.15) is a 35-mer basic peptide from the venom of the Iranian scorpion Hemiscorpius lepturus, which reversibly blocks Kv1.1, Kv1.2 and Kv1.3 voltage-gated K+ channels.{{cite journal|last=Srairi-Abid|first=N. |author2=Shahbazzadeh, D. |author3=Chatti, I. |author4=Mlayah-Bellalouna, S. |author5=Mejdoub, H. |author6=Borchani, L. |author7=Benkhalifa, R. |author8=Akbari, A. |author9=Ayeb, M. E.|title=Hemitoxin, the first potassium channel toxin from the venom of the Iranian scorpion Hemiscorpius lepturus|journal=FEBS Journal|year=2008|volume=275|issue=18 |pages=4641–4650|doi=10.1111/j.1742-4658.2008.06607.x|pmid=18699777 |doi-access=free}}
Sources
HTX is a neurotoxin derived from the venom of the scorpion Hemiscorpius lepturus, which is found in the southwest province of Iran, Khuzestan. Hemitoxin constitutes about 0.1% of all venom proteins found in the Hemiscorpius lepturus venom gland.
Chemistry
HTX is a peptide composed of 35 amino acids including eight cysteine residues which are cross linked forming four intramolecular cystine amino acids via disulfide bridges. It belongs to subfamily 6 of the α-KTx family of potassium channel scorpion toxins and has the highest sequence similarity with Maurotoxin (MTX), which is derived from a Tunisian scorpion called Scorpio maurus palmatus. MTX is also a K+ channel blocker but is composed of 34 amino acids instead of 35.
Target
HTX is a voltage-gated K+ channel blocker peptide. It reversibly blocks type Kv1.1, Kv1.2 and Kv1.3 channels with IC50 values of 13, 16 and 2 nM, respectively. HTX has a different affinity for K+ channels. It appears to be 20 times less potent on Kv1.2 channels and 90 times more potent on Kv1.3 channels than the α-KTx6 family member MTX.