Tucker S J, Pessia M, Adelman J P
Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland 97201, USA.
Am J Physiol. 1996 Jul;271(1 Pt 2):H379-85. doi: 10.1152/ajpheart.1996.271.1.H379.
Coexpression in Xenopus oocytes of the cloned cardiac inward rectifier subunits Kir 3.1 and Kir 3.4 results in G protein-stimulated channel activity closely resembling the muscarinic channel underlying the inwardly rectifying K+ current in atrial myocytes. To determine the stoichiometry and relative subunit positions within the channel, Kir 3.1 and Kir 3.4 were coexpressed in varying ratios with cloned G beta 1 gamma 2 subunits and also as tandemly linked tetramers with different relative subunit positions. The results reveal that the most efficient channel comprises two subunits of each type in an alternating array within the tetramer. To localize regions important for subunit coassembly and G protein sensitivity, chimeric subunits containing domains from either Kir 3.1, Kir 3.4, or the G protein-insensitive subunit Kir 4.1 were expressed. The results demonstrate that the transmembrane domains dictate the potentiation of the coassembled channels and that, although the NH4- or COOH-termini of both subunits alone can confer G protein sensitivity, both termini are required for maximal stimulation by G beta 1 gamma 2.
在非洲爪蟾卵母细胞中共同表达克隆的心脏内向整流亚基Kir 3.1和Kir 3.4，会产生G蛋白刺激的通道活性，该活性与心房肌细胞内向整流钾电流基础的毒蕈碱通道极为相似。为了确定通道内的化学计量和相对亚基位置，将Kir 3.1和Kir 3.4与克隆的Gβ1γ2亚基以不同比例共同表达，并且还作为具有不同相对亚基位置的串联连接四聚体表达。结果表明，最有效的通道在四聚体内由每种类型的两个亚基以交替排列组成。为了定位对亚基共组装和G蛋白敏感性重要的区域，表达了包含来自Kir 3.1、Kir 3.4或G蛋白不敏感亚基Kir 4.1结构域的嵌合亚基。结果表明，跨膜结构域决定了共组装通道的增强作用，并且，虽然两个亚基单独的NH4-或COOH末端都可以赋予G蛋白敏感性，但两个末端对于Gβ1γ2的最大刺激都是必需的。
