Hurst R S, Busch A E, Kavanaugh M P, Osborne P B, North R A, Adelman J P
Vollum Institute, Oregon Health Sciences University, Portland 97201.
Mol Pharmacol. 1991 Oct;40(4):572-6.
alpha-Dendrotoxin (DTX) is a 60-amino acid peptide belonging to the family of mamba snake neurotoxins; it is a potent blocker of some but not all voltage-gated potassium currents. Potassium currents recorded from oocytes injected with cloned potassium channel RNAs also vary in sensitivity to DTX. Expression of channels that were chimeras of the DTX-sensitive channel RBK2 and the DTX-insensitive channel RGK5 showed that the putative extracellular loop between transmembrane domains S5 and S6 contributes strongly to DTX sensitivity. Mutation of two residues (Ala352Glu353) in this region of RBK1 to conform to those at equivalent positions in RGK5 (Pro374Ser375) reduced the potency of DTX about 70-fold, and the substitution of Tyr379 in RBK1 by its counterpart in RGK5 (His401) caused an additional 2.5-fold decrease in sensitivity. Converse substitutions in RGK5 significantly increased sensitivity to DTX. The results suggest that these residues contribute significantly to the channel-toxin interaction, providing further evidence that the S5-S6 loop lies at or near the external mouth of the channel, where DTX binding leads to channel occlusion. They offer a molecular explanation for the differences in DTX sensitivity observed among native potassium channels.
α-树突毒素（DTX）是一种由60个氨基酸组成的肽，属于曼巴蛇神经毒素家族；它是部分而非所有电压门控钾电流的强效阻滞剂。从注射了克隆钾通道RNA的卵母细胞中记录到的钾电流对DTX的敏感性也存在差异。对DTX敏感通道RBK2和DTX不敏感通道RGK5的嵌合通道的表达研究表明，跨膜结构域S5和S6之间假定的细胞外环对DTX敏感性有很大影响。将RBK1该区域的两个残基（Ala352Glu353）突变为与RGK5中对应位置的残基（Pro374Ser375）一致，可使DTX的效力降低约70倍，并且将RBK1中的Tyr379替换为RGK5中的对应残基（His401）会导致敏感性额外降低2.5倍。在RGK5中进行相反的替换则显著提高了对DTX的敏感性。这些结果表明，这些残基对通道-毒素相互作用有显著贡献，进一步证明了S5-S6环位于通道外口或其附近，DTX结合在此处会导致通道阻塞。它们为天然钾通道之间观察到的DTX敏感性差异提供了分子解释。
