Tzounopoulos T, Guy H R, Durell S, Adelman J P, Maylie J
Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
Proc Natl Acad Sci U S A. 1995 Oct 10;92(21):9593-7. doi: 10.1073/pnas.92.21.9593.
Injection of min K mRNA into Xenopus oocytes results in expression of slowly activating voltage-dependent potassium channels, distinct from those induced by expression of other cloned potassium channels. The min K protein also differs in structure, containing only a single predicted transmembrane domain. While it has been demonstrated that all other cloned potassium channels form by association of four independent subunits, the number of min K monomers which constitute a functional channel is unknown. In rat min K, replacement of Ser-69 by Ala (S69A) causes a shift in the current-voltage (I-V) relationship to more depolarized potentials; currents are not observed at potentials negative to 0 mV. To determine the subunit stoichiometry of min K channels, wild-type and S69A subunits were coexpressed. Injections of a constant amount of wild-type mRNA with increasing amounts of S69A mRNA led to potassium currents of decreasing amplitude upon voltage commands to -20 mV. Applying a binomial distribution to the reduction of current amplitudes as a function of the different coinjection mixtures yielded a subunit stoichiometry of at least 14 monomers for each functional min K channel. A model is presented for how min K subunits may form a channel.
将小电导钙激活钾通道（min K）mRNA注射到非洲爪蟾卵母细胞中，会导致缓慢激活的电压依赖性钾通道的表达，这与其他克隆钾通道表达所诱导的通道不同。min K蛋白在结构上也有所不同，仅包含一个预测的跨膜结构域。虽然已经证明所有其他克隆的钾通道都是由四个独立亚基结合形成的，但构成功能性通道的min K单体数量尚不清楚。在大鼠min K中，将丝氨酸69（Ser-69）替换为丙氨酸（S69A）会导致电流-电压（I-V）关系向更去极化的电位偏移；在负于0 mV的电位下未观察到电流。为了确定min K通道的亚基化学计量，共表达了野生型和S69A亚基。将恒定数量的野生型mRNA与越来越多的S69A mRNA一起注射，在电压指令为-20 mV时，钾电流幅度会降低。将电流幅度的降低作为不同共注射混合物的函数应用二项分布，得出每个功能性min K通道的亚基化学计量至少为14个单体。本文提出了一个关于min K亚基如何形成通道的模型。
