The amino acid sequence of Iberiotoxin [1] |
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Pyr - Phe - Thr - Asp - Val - Asp - Cys - Ser - Val - Ser - Lys - Glu - Cys - Trp - Ser - Val - Cys - Lys - Asp - Leu - Phe - Gly - Val - Asp - Arg - Gly - Lys - Cys - Met - Gly - Lys - Lys - Cys - Arg - Cys - Tyr - Gln - OH |
Disulfide bridges: Cys7 - Cys28, Cys13 - Cys33, Cys17 - Cys35 |
Iberiotoxin (IbTX) is an ion channel toxin purified from the Eastern Indian red scorpion Hottentotta tamulus . Iberiotoxin selectively inhibits the current through large-conductance calcium-activated potassium channels.
Iberiotoxin is a 37-amino acid peptide. The formula is C179H274N50O55S7. [2] It is also known as "Potassium channel toxin alpha-KTx 1.3" or IbTx. The complete amino acid sequence has been defined and it displays 68% sequence homology with charybdotoxin. [1]
Iberiotoxin binds to the outer face of the large-conductance calcium-activated potassium channels (maxiK or BK channels) with high affinity (Kd ~1 nM). [3] It selectively inhibits the current by decreasing both the probability of opening and the open time of the channel. [3]
The venom produces mainly cardiopulmonary abnormalities like circulatory derangements, myocarditis and changes in cardiac sarcolemmal ATPase and by these abnormalities it can finally cause death. In rural India the scorpion and its venom is a commonly known factor of children's death. The venom initially causes transient cholinergic stimulation (vomiting, profuse sweating, bradycardia, priapism, hypersalivation, and hypotension) which is followed by sustained adrenergic hyperactivity (hypertension, tachycardia, and myocardial failure). The adrenergic phase but not the cholinergic phase is a dose-dependent phenomenon. [4]
Treatment is mainly symptomatic. Local pain is treated by injecting dehydroemetine at the site of the sting. Hypovolaemia is corrected by oral rehydration solution. Agitated, confused and non-cooperative patients are given a 5% dextrose saline drip. Patients with hypertension on admission are given a single dose of 5 mg sublingual nifedipine and oral prazosin. The blood pressure in patients with hypertension is controlled with sublingual nifedipine alone. Patients with pulmonary oedema are propped up and given intravenous aminophylline, intravenous sodium bicarbonate, oral prazosin, and oxygen by mask. [4]
Charybdotoxin (ChTX) is a 37 amino acid neurotoxin from the venom of the scorpion Leiurus quinquestriatus hebraeus (deathstalker) that blocks calcium-activated potassium channels. This blockade causes hyperexcitability of the nervous system. It is a close homologue of agitoxin and both toxins come from Leiurus quinquestriatus hebraeus. It is named after Charybdis, a sea monster from Greek myth.
Prazosin, sold under the brand name Minipress among others, is a medication used to treat high blood pressure, symptoms of an enlarged prostate, and nightmares related to post-traumatic stress disorder (PTSD). It is an α1 blocker. It is a less preferred treatment of high blood pressure. Other uses may include heart failure and Raynaud syndrome. It is taken by mouth.
SK channels are a subfamily of calcium-activated potassium channels. They are so called because of their small single channel conductance in the order of 10 pS. SK channels are a type of ion channel allowing potassium cations to cross the cell membrane and are activated (opened) by an increase in the concentration of intracellular calcium through N-type calcium channels. Their activation limits the firing frequency of action potentials and is important for regulating afterhyperpolarization in the neurons of the central nervous system as well as many other types of electrically excitable cells. This is accomplished through the hyperpolarizing leak of positively charged potassium ions along their concentration gradient into the extracellular space. This hyperpolarization causes the membrane potential to become more negative. SK channels are thought to be involved in synaptic plasticity and therefore play important roles in learning and memory.
Calciseptine (CaS) is a natural neurotoxin isolated from the black mamba Dendroaspis p. polylepis venom. This toxin consists of 60 amino acids with four disulfide bonds. Calciseptine specifically blocks L-type calcium channels, but not other voltage-dependent Ca2+ channels such as N-type and T-type channels.
Tityustoxin is a toxin found in the venom of scorpions from the subfamily Tityinae. By binding to voltage-dependent sodium ion channels and potassium channels, they cause sialorrhea, lacrimation and rhinorrhea.
Slotoxin is a peptide from Centruroides noxius Hoffmann scorpion venom. It belongs to the short scorpion toxin superfamily.
Maurotoxin is a peptide toxin from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus, from which it was first isolated and from which the chemical gets its name. It acts by blocking several types of voltage-gated potassium channel.
Margatoxin (MgTX) is a peptide that selectively inhibits Kv1.3 voltage-dependent potassium channels. It is found in the venom of Centruroides margaritatus, also known as the Central American Bark Scorpion. Margatoxin was first discovered in 1993. It was purified from scorpion venom and its amino acid sequence was determined.
Tamapin is a toxin from the Indian Red Scorpion, which is a selective and potent blocker of SK2 channels.
Kaliotoxin (KTX) inhibits potassium flux through the Kv1.3 voltage-gated potassium channel and calcium-activated potassium channels by physically blocking the channel-entrance and inducing a conformational change in the K+-selectivity filter of the channel.
Hottentotta is a genus of scorpions of the family Buthidae. It is distributed widely across Africa, except for most of the Sahara desert. Species in the genus also occur in the Middle East, the Arabian Peninsula, southeastern Turkey, Iraq, Iran, Afghanistan, Pakistan, India, Nepal, Cape Verde Islands, and Sri Lanka (introduced).
Himmatrao Saluba Bawaskar is an Indian physician from Mahad, Maharashtra. He is known for his research on treatment for scorpion stings. Much of his work has been published in the British medical journal The Lancet. He has also conducted research in the fields of snake bites, cardiovascular diseases, and hypothyroidism.
Pandinotoxins are toxins from the venom of the emperor scorpion Pandinus imperator. They are selective blockers of voltage-gated potassium channels
Anuroctoxin is a peptide from the venom of the Mexican scorpion Anuroctonus phaiodactylus. This neurotoxin belongs to the alpha family of potassium channel acting peptides. It is a high-affinity blocker of Kv1.3 channels.
Pi3 toxin is a purified peptide derivative of the Pandinus imperator scorpion venom. It is a potent blocker of voltage-gated potassium channel, Kv1.3 and is closely related to another peptide found in the venom, Pi2.
Tamulotoxin is a venomous neurotoxin from the Indian Red Scorpion.
HsTx1 is a toxin from the venom of the scorpion Heterometrus spinifer. HsTx1 is a very potent inhibitor of the rat Kv1.3 voltage-gated potassium channel.
Pi4 is a short toxin from the scorpion Pandinus imperator that blocks specific potassium channels.
Limbatustoxin, is an ion channel toxin from the venom of the Centruroides limbatus scorpion. This toxin is a selective blocker of BK channels, calcium-activated potassium channels.
Noxiustoxin (NTX) is a toxin from the venom of the Mexican scorpion Centruroides noxius Hoffmann which block voltage-dependent potassium channels and calcium-activated potassium channels.