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Apamin is a neurotoxin that was originally isolated from Apis mellifera. Apamin binds to and inhibits the SK channels (small conductance Ca2+-activated K+ channels) in the brain and spinal cord. Apamin inhibits three subtypes of SK channels (KCa2.1, KCa2.2, and KCa2.3) with different affinity. Apamin does not affect KCa3.1 channel activity. Apamin most likely acts as a pore blocker such as Scyllatoxin or Tamapin, although residues both inside and outside of the pore region of the SK channels participate in apamin binding. The SK channels are present in a wide range of excitable and non-excitable cells, including cells in the central nervous system, intestinal myocytes, endothelial cells, and hepatocytes.
AA sequence: H-Cys1-Asn-Cys3-Lys-Ala-Pro-Glu-Thr-Ala-Leu-Cys11-Ala-Arg-Arg-Cys15-Gln-Gln-His-NH2
Disulfide bonds: Cys1-Cys11 and Cys3-Cys15
Length (aa): 18
Formula: C79H131N31O24S4
Molecular Weight: 2027.34 Da
Appearance: White lyophilized solid
Solubility: water and saline buffer
CAS number: [24345-16-2]
Source: Synthetic
Purity rate: > 98 %
Many venom toxins interfere with ion channel function. Toxins, as specific, high affinity ligands, have played an important part in purifying and characterizing many ion channel proteins. Our knowledge of potassium ion channel structure is meager because until recently, no specific potassium channel toxins were known, or identified as such. This review summarizes the sudden explosion of research on potassium channel toxins that has occurred in recent years. Toxins are discussed in terms of their structure, physiological and pharmacological properties, and the characterization of toxin binding sites on different subtypes of potassium ion channels.
Strong PN (1990). Potassium channel toxins. Pharmacol Ther. PMID: 2181489
Several recently characterized toxins (apamin, charybdotoxin, dendrotoxin and noxiustoxin) are proving invaluable for establishing what kinds of potassium channel are expressed in neurones, and what the roles of the channels might be.
Castle NA. et al. (1989). Toxins in the characterization of potassium channels. Trends Neurosci. PMID: 2469212
