Mayorga-Wark O, Costantin J, Dubinsky W P, Schultz S G
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
Am J Physiol. 1993 Aug;265(2 Pt 1):C541-7. doi: 10.1152/ajpcell.1993.265.2.C541.
We have previously demonstrated that a synthetic peptide composed of the first 22 amino acids from the NH2-terminus of the Shaker B K+ channel protein deactivates a voltage-dependent K+ channel present in basolateral membrane of Necturus small intestinal epithelial cells reconstituted into planar lipid bilayers (Dubinsky et al. Proc. Natl. Acad. Sci. USA 89: 1770-1774, 1992). We now demonstrate that this peptide interacts with the inner surface of the Necturus channel only when it is in the open or conducting configuration and that this interaction is hindered by tetraethylammonium ion, a well-established blocker of this and other K+ channels. We conclude that this peptide is an open-pore blocker of the Necturus K+ channel as it appears to be in the case of the Shaker B K+ channel. We further demonstrate that trypsin, which abolishes the ability of this peptide to block both the Necturus and the Shaker K+ channels and inhibits spontaneous inactivation of the Shaker K+ channel, also impairs the voltage-gate of the Necturus K+ channel. These findings, and others to be reported in a companion paper, suggest structural homologies between the "inactivation peptide" of the Shaker B K+ channel and the voltage-gate of the Necturus K+ channel.
我们之前已经证明，一种由Shaker B钾通道蛋白NH2末端的前22个氨基酸组成的合成肽，能够使存在于大鲵小肠上皮细胞基底外侧膜中的一种电压依赖性钾通道失活，该细胞已被重构成平面脂质双层（Dubinsky等人，《美国国家科学院院刊》89: 1770 - 1774, 1992）。我们现在证明，这种肽仅在处于开放或传导构型时才与大鲵通道的内表面相互作用，并且这种相互作用受到四乙铵离子的阻碍，四乙铵离子是该钾通道和其他钾通道的一种公认的阻滞剂。我们得出结论，这种肽是大鲵钾通道的一种开放孔道阻滞剂，就像它在Shaker B钾通道的情况一样。我们进一步证明，胰蛋白酶消除了这种肽阻断大鲵和Shaker钾通道的能力，并抑制了Shaker钾通道的自发失活，同时也损害了大鲵钾通道的电压门控。这些发现以及将在一篇配套论文中报道的其他发现，表明了Shaker B钾通道的“失活肽”与大鲵钾通道的电压门控之间存在结构同源性。
