Protein_length= 46 (precursor)
Taxa= Apis mellifera (
Cells= Venom Gland
EntrezGene = 406135
RefSeq = NP_001011612.1
UniProt = P01500
SK channelChembox new
ImageFile = Apamin.svg
ImageSize = 300px
Reference = [ [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=16133797 Apamin - Compound Summary] ,
Section1 = Chembox Identifiers
PubChem = 16133797
CASNo = 24345-16-2
Section2 = Chembox Properties
Formula = C79H131N31O24S4
MolarMass = 2027.33874 g/mol
Section3 = Chembox Hazards
Apamin is a
neurotoxinwhich selectively blocks SK channels, a type of Ca2+-activated K+ channels expressed in the central nervous system. The final 18 amino acid polypeptideis a component of apitoxin( bee venom). [Habermann E. "Apamin." "Pharmacology and Therapeutics". 1984; 25(2):255-70. PMID 6095335] It is used primarily in biomedical research to study the electrical properties of SK channels and their role in the afterhyperpolarizations occurring immediately following an action potential. [Castle NA, Haylett DG, Jenkinson DH. "Toxins in the characterization of potassium channels." "Trends in Neurosciences". 1989 Feb;12(2): 59-65. PMID 2469212]
Apamin is a neurotoxin that was originally isolated from "Apis mellifera", the
Western honey bee. The venomof the honeybeeconsists of many more products, like melittin, the MCD peptideand phospholipase A2.
Apamin is a
polypeptidepossessing an amino acidsequence of H-Cys-Asn-Cys-Lys-Ala-Pro-Glu-Thr-Ala-Leu-Cys-Ala-Arg-Arg-Cys-Gln-Gln-His-NH2 (with disulfide bondsbetween Cys1-Cys11 and Cys3-Cys15). Because honeybee venom is a complex mixture of short peptides and proteins, it is difficult to isolate apamin. The isolation can be done by electrophoresis, [Hartter P, Weber U. "Basic peptides from bee venom, I: isolation, reduction and reoxidation of apamin and MCD-peptide." "Hoppe Seylers Z Physiol Chem". 1975 Jun; 356(6):693-9. PMID 1181269] or by chromatography. [Räder K, Wildfeuer A, Wintersberger F, Bossinger P, Mücke HW. "Characterization of bee venom and its main components by high-performance liquid chromatography." "Journal of Chromatography". 1987 Nov 6;408:341-8. PMID 3429530] [Loseva OI, Gavryushkin AV, Osipov VV, Vanyakin EN. "Application of free-flow electrophoresis for isolation and purification of proteins and peptides." "Electrophoresis". 1998 Jun;19(7):1127-34. PMID 9662174]
Apamin binds to the SK channels (small conductance Ca2+-activated K+ channels) in the
brainand spinal cordand inhibits them. [Fletcher DI, Ganellin CR, Piergentili A, Dunn PM, Jenkinson DH. "Synthesis and pharmacological testing of polyaminoquinolines as blockers of the apamin-sensitive Ca2+-activated K+ channel (SK(Ca))." "Bioorganic Medical Chemistry". 2007 Aug 15;15(16):5457-79. PMID 17560109] It inhibits the three cloned SK channel subtypes (SK1, SK2, and SK3) with different affinity, highest affinity for SK2, lowest for SK1, and intermediate for SK3 channels. Heteromers show intermediate sensitivity. Most likely, apamin acts as a pore blocker, although residues both inside and outside of the pore region of the SK channels participate in apamin binding.Nolting, A., Ferraro, T. D'hoedt, D. and Stocker, M. "An Amino Acid Outside the Pore Region Influences Apamin Sensitivity in Small Conductance Ca2+-activated K+ Channels." "Journal of Biological Chemistry". 2007 282, 3478-3486. PMID 17142458] 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.SK channels, when activated, contribute to afterhyperpolarizations in neurons, which control neuronal excitability. Intracellular Ca2+ binding to calmodulincan activate these channels. Channel deactivation can take place through dissociation of Ca2+ from calmodulin. Stocker M. "Ca(2+)-activated K+ channels: molecular determinants and function of the SK family." "Nature Reviews Neuroscience". 2004 Oct;5(10):758-70. PMID 15378036] Inhibition of SK channels by apamin will increase the neuronal excitability and lower the threshold for generating an action potential.Other toxins that block SK channels are tamapinand scyllatoxin.
Symptoms following bee sting or apamin poisoning may include:
*local effects: burning or stinging
pain, swelling, redness.
*severe systemic reactions: swelling of the
tongueand throat, difficulty breathing, and shock.
optic neuritisand atrophy.
atrial fibrillation, cerebral infarction, acute myocardial infarction, Fisher's syndrome, acute inflammatory polyradiculopathy( Guillain-Barre syndrome), claw hand(through a central action of apamin on the spinal cordand a peripheral action in the form of median and ulnar neuritis, causing spasms of the long flexors in the forearm).R. Saravanan R, King J, White J. "Transient claw hand owing to a bee sting. A report of two cases." "The Journal of Bone and Joint Surgery (Br)". 2004;86-B;404-5. PMID 15125129]
*dramatic haemorrhagic effect in the
lungs. [Lallement G, Fosbraey P, Baille-Le-Crom V, Tattersall JE, Blanchet G, Wetherell JR, Rice P, Passingham SL, Sentenac-Roumanou H. "Compared toxicity of the potassium channel blockers, apamin and dendrotoxin." "Toxicology". 1995 Dec 15;104(1-3):47-52. PMID 8560501]
SK channelblockers such as apamin can have therapeutic applications, for example on the peripheral cells (e.g. the insulinreleasing cells of the pancreas) and on the central nervous systemwhere there is evidence for a role of SK channels in memoryprocesses, both general and specifically hippocampal.
SK channels have been proposed as targets for the treatment of
ataxia, epilepsy, memory disorders, and possibly schizophreniaand Parkinson's disease.
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