Ketchum K A, Joiner W J, Sellers A J, Kaczmarek L K, Goldstein S A
Department of Pediatrics, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06536-0812, USA.
Nature. 1995 Aug 24;376(6542):690-5. doi: 10.1038/376690a0.
Potassium channels catalyse the permeation of K+ ions across cellular membranes and are identified by a common structural motif, a highly conserved signature sequence of eight amino acids in the P domain of each channel's pore-forming alpha-subunit. Here we describe a novel K+ channel (TOK1) from Saccharomyces cerevisiae that contains two P domains within one continuous polypeptide. Xenopus laevis oocytes expressing the channel exhibit a unique, outwardly rectifying, K(+)-selective current. The channel is permeable to outward flow of ions at membrane potentials above the K+ equilibrium potential; its conduction-voltage relationship is thus sensitive to extracellular K+ ion concentration. In excised membrane patches, external divalent cations block the channel in a voltage-dependent manner, and their removal in this configuration allows inward channel current. These attributes are similar to those described for inwardly rectifying K+ channels, but in the opposite direction, a previously unrecognized channel behaviour. Our results identify a new class of K+ channel which is distinctive in both its primary structure and functional properties. Structural homologues of the channel are present in the genome of Caenorhabditis elegans.
钾通道催化钾离子穿过细胞膜，其通过一个共同的结构基序来识别，即每个通道的成孔α亚基的P结构域中有一个由八个氨基酸组成的高度保守的特征序列。在此，我们描述了一种来自酿酒酵母的新型钾通道（TOK1），它在一个连续的多肽中包含两个P结构域。表达该通道的非洲爪蟾卵母细胞表现出一种独特的、外向整流的、钾离子选择性电流。该通道在膜电位高于钾离子平衡电位时对离子外流具有通透性；因此，其传导-电压关系对细胞外钾离子浓度敏感。在切除的膜片上，外部二价阳离子以电压依赖的方式阻断该通道，在此配置下去除它们可使通道产生内向电流。这些特性与内向整流钾通道所描述的特性相似，但方向相反，这是一种以前未被认识到的通道行为。我们的结果鉴定出了一类新的钾通道，其在一级结构和功能特性上都很独特。该通道的结构同源物存在于秀丽隐杆线虫的基因组中。
