Cao Y, Crawford N M, Schroeder J I
Department of Biology, University of California at San Diego, La Jolla 92093-0116, USA.
J Biol Chem. 1995 Jul 28;270(30):17697-701.
The Arabidopsis hyperpolarization-activated (inward-rectifying) K+ channel KAT1 is structurally more similar to animal depolarization-activated (outward-rectifying) K+ channels than to animal hyperpolarization-activated K+ channels. To gain insight into the structural basis for the opposite voltage dependences of plant inward-rectifying and animal outward-rectifying K+ channels, we constructed recombinant chimeric channels between the hyperpolarization-activated K+ channel KAT1 and a Xenopus depolarization-activated K+ channel. We report here that two of the chimeric constructs, which contain the first third of the KAT1 sequence, including the first four membrane-spanning segments (S1-S4) and the linker sequence between the fourth and fifth membrane-spanning segments, express functional channels that retain activation by hyperpolarization, but not depolarization. These two chimeric channels are no longer selective for K+. The chimeras are selective for cations over anions and are permeable to Ca2+. Therefore, unlike animal hyperpolarization-activated K+ channels, in which the carboxyl terminus is important for inward rectification induced by Mg2+ and polyamine block, the plant KAT1 channel has its major determinants for inward rectification in the amino-terminal region, which ends at the end of the S4-S5 linker.
拟南芥超极化激活（内向整流）钾离子通道KAT1在结构上与动物去极化激活（外向整流）钾离子通道的相似性高于与动物超极化激活钾离子通道的相似性。为了深入了解植物内向整流钾离子通道和动物外向整流钾离子通道相反电压依赖性的结构基础，我们构建了超极化激活钾离子通道KAT1与非洲爪蟾去极化激活钾离子通道之间的重组嵌合通道。我们在此报告，两个嵌合构建体包含KAT1序列的前三分之一，包括前四个跨膜片段（S1-S4）以及第四和第五跨膜片段之间的连接序列，表达的功能性通道保留了通过超极化而非去极化激活的特性。这两个嵌合通道对钾离子不再具有选择性。嵌合体对阳离子的选择性高于阴离子，并且可通透Ca2+。因此，与动物超极化激活钾离子通道不同，在动物超极化激活钾离子通道中羧基末端对于Mg2+和多胺阻滞诱导的内向整流很重要，而植物KAT1通道内向整流的主要决定因素位于氨基末端区域，该区域在S4-S5连接序列末端结束。
