title: Fluorescence resonance energy transfer on the voltage-dependent sodium channel. Spatial relationship and site coupling between the batrachotoxin and Leiurus quinquestriatus quinquestriatus alpha-scorpion toxin receptors.
abstract: A fluorescent N- methylanthraniloyl derivative of the potent depolarizing agent batrachotoxin has been used to probe the structural and conformational properties of the neurotoxin receptor site on the voltage-dependent sodium channel. Batrachotoxin A 20-alpha-N- methylanthranilate (BTX-NMA) retains high affinity for its receptor site on the synaptosomal sodium channel with a Kd between 78 and 91 nM and an average site capacity of 2 pmol/mg of synaptosomal protein in the presence of Leiurus quinquestriatus quinquestriatus alpha-scorpion toxin. The fluorescence emission of BTX-NMA upon binding to synaptosomes indicates a hydrophobic environment. Toxin V from L. quinquestriatus, an allosteric activator, effects a 20-nm red shift in the spectrum of bound BTX-NMA and a 4-fold enhancement in the fluorescence quantum yield disclosing a conformational change into a hydrophilic environment. Fluorescence resonance energy transfer measurements show that the distance separating the receptor sites is 37 +/- 10 A. Thus, the binding of alpha-scorpion toxin must involve conformational changes that extend over large distances from the batrachotoxin-binding locus. This information together with the distance measurements between the tetrodotoxin and alpha-scorpion toxin receptors and the conformational transition associated with this distance upon batrachotoxin addition indicate a conformationally flexible channel with coupling of sites through the polyatomic framework of individual subunits or through extensive alterations in subunit/subunit interactions.
mesh_terms: D000818:Animals; D001496:Batrachotoxins / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D004735:Energy Transfer; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D011950:Receptors, Cholinergic / Q000378:metabolism*; D012605:Scorpions; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D001496:Batrachotoxins; D007473:Ion Channels; D011950:Receptors, Cholinergic; D015222:Sodium Channels; C041417:batrachotoxin receptor; C029574:scorpion toxin receptor; C031775:batrachotoxinin A 20-alpha-benzoate; D012964:Sodium