Harvey A L, Vatanpour H, Rowan E G, Pinkasfeld S, Vita C, Ménez A, Martin-Eauclaire M F
Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, U.K.
Toxicon. 1995 Apr;33(4):425-36. doi: 10.1016/0041-0101(94)00181-7.
Scorpion venoms contain toxins that block different types of potassium channels. Some of these toxins have affinity for high conductance Ca(2+)-activated K+ channels and for dendrotoxin-sensitive voltage-dependent K+ channels. The structural features that determine the specificity of binding to different channel types are not known. We investigated this using natural and synthetic scorpion toxins. We have tested the effects of charybdotoxin (CTX) and two homologues (Lqh 15-1 and Lqh 18-2), iberiotoxin (IbTX), and kaliotoxin (KTX) from the scorpions Leiurus quinquestriatus hebreus, Buthus tamulus and Androctonus mauretanicus mauretanicus, respectively, and synthetic variants of CTX, namely CTX2-37, CTX3-37, CTX4-37, and CTX7-37, on a Ca(2+)-activated K+ current (IK-Ca) at a mammalian motor nerve terminal, and on the binding of a radiolabelled dendrotoxin, 125I-DpI, to voltage-dependent K+ channels on rat brain synaptosomal membranes. The native toxins contain 37-38 amino acid residues, they are over 30% identical in sequence (CTX and IbTX are 68% identical), and they have similar three-dimensional conformations. All toxins, except IbTX, displaced 125I-DpI from its synaptosomal binding sites: Lqh 18-2 (Ki = 0.25 nM), KTX (Ki = 2.1 nM), CTX (Ki = 3.8 nM), CTX2-37, (Ki = 30 nM), Lqg 15-1 (Ki = 50 nM), CTX3-37 (Ki = 60 nM), CTX4-37 (Ki = 50 nM), CTX7-37 (Ki = 105 nM). IbTX had no effect at 3 microM. When variants of CTX with deletions at the N-terminal portion were tested for their activity on IK-Ca on motor nerve terminals in mouse triangularis sterni nerve-muscle preparations, CTX3-37 and CTX4-37 were ineffective at 100 nM; and CTX7-37 was ineffective at up to 1 microM. IbTX and CTX (100 nM) completely blocked IK-Ca, but KTX (100 nM) did not affect the nerve terminal IK-Ca. Different residues appear to be important for interactions of the toxins with different K+ channels. IbTX did not displace dendrotoxin binding, but it did block IK-Ca, whereas KTX was as active as CTX against dendrotoxin binding but it did not affect the IK-Ca of the motor nerve terminals. The N-terminal section of the toxins appears to be particularly involved in block of IK-Ca at the motor nerve terminal: it is truncated in the inactive synthetic CTX variants; and it is positively charged at lysine-6 in KTX (which is inactive), but negatively charged in IbTX and neutral in CTX.(ABSTRACT TRUNCATED AT 400 WORDS)
蝎毒含有能阻断不同类型钾通道的毒素。其中一些毒素对高电导钙激活钾通道和对树突毒素敏感的电压依赖性钾通道具有亲和力。决定与不同通道类型结合特异性的结构特征尚不清楚。我们使用天然和合成蝎毒素对此进行了研究。我们测试了来自以色列金蝎、印度红蝎和摩洛哥杀人蝎的蝎毒素氯毒素（CTX）及其两种同系物（Lqh 15 - 1和Lqh 18 - 2）、iberiotoxin（IbTX）和卡利毒素（KTX），以及CTX的合成变体，即CTX2 - 37、CTX3 - 37、CTX4 - 37和CTX7 - 37，对哺乳动物运动神经末梢上的钙激活钾电流（IK - Ca），以及对放射性标记的树突毒素125I - DpI与大鼠脑突触体膜上电压依赖性钾通道结合的影响。天然毒素含有37 - 38个氨基酸残基，它们的序列一致性超过30%（CTX和IbTX的序列一致性为68%），并且具有相似的三维构象。除IbTX外，所有毒素都能从其突触体结合位点取代125I - DpI：Lqh 18 - 2（Ki = 0.25 nM）、KTX（Ki = 2.1 nM）、CTX（Ki = 3.8 nM）、CTX2 - 37（Ki = 3 nM）、Lqg 15 - 1（Ki = 5 nM）、CTX3 - 37（Ki = 6 nM）、CTX4 - 37（Ki = 5 nM）、CTX7 - 37（Ki = 105 nM）。3 μM的IbTX没有作用。当测试N端部分缺失的CTX变体对小鼠三角肌神经 - 肌肉标本中运动神经末梢上IK - Ca的活性时，CTX3 - 37和CTX4 - 37在100 nM时无效；CTX7 - 37在高达1 μM时无效。IbTX和CTX（100 nM）完全阻断IK - Ca，但KTX（100 nM）不影响神经末梢IK - Ca。不同的残基对于毒素与不同钾通道的相互作用似乎很重要。IbTX不能取代树突毒素的结合，但它能阻断IK - Ca，而KTX在对抗树突毒素结合方面与CTX一样有效，但它不影响运动神经末梢的IK - Ca。毒素的N端部分似乎特别参与了对运动神经末梢IK - Ca的阻断：在无活性的合成CTX变体中它被截断；在无活性的KTX中赖氨酸 - 6带正电荷，但在IbTX中带负电荷，在CTX中呈中性。（摘要截断于400字）
