Inagaki N, Gonoi T, Seino S
Division of Molecular Medicine, Center for Biomedical Science, Chiba University School of Medicine, Chuo-ku, Japan.
FEBS Lett. 1997 Jun 9;409(2):232-6. doi: 10.1016/s0014-5793(97)00488-2.
We have investigated the subunit stoichiometry of the pancreatic beta-cell ATP-sensitive K+ (KATP) channel (SUR1/Kir6.2 channel) by constructing cDNA encoding a single polypeptide (beta alpha polypeptide) consisting of a SUR1 (beta) subunit and a Kir6.2 (alpha) subunit. 86Rb+ efflux and single-channel properties of COS1 cells expressing beta alpha polypeptides were similar to those of COS1 cells coexpressing alpha monomers and beta monomers. Coexpression of beta alpha polypeptides with alpha monomers inhibited the K+ currents, while coexpression with beta monomers did not. We then constructed another single polypeptide (beta alpha2) consisting of a beta subunit and a dimeric repeat of the alpha subunit. 86Rb+ efflux from COS1 cells expressing beta alpha2 polypeptides was small, but was restored by supplementation with beta monomers. These results indicate that the activity of K(ATP) channels is optimized when the alpha and beta subunits are coexpressed with a molar ratio of 1:1. Since inward rectifier K+ channels are thought to function as homo- or hetero-tetramers, this suggests that the K(ATP) channel functions as a multimeric protein, most likely a hetero-octamer composed of a tetramer of the Kir6.2 subunit and a tetramer of the SUR1 subunit.
我们通过构建编码由一个SUR1（β）亚基和一个Kir6.2（α）亚基组成的单一多肽（βα多肽）的cDNA，研究了胰腺β细胞ATP敏感性钾离子（KATP）通道（SUR1/Kir6.2通道）的亚基化学计量。表达βα多肽的COS1细胞的86Rb+外流和单通道特性与共表达α单体和β单体的COS1细胞相似。βα多肽与α单体共表达会抑制钾离子电流，而与β单体共表达则不会。然后我们构建了另一种由一个β亚基和α亚基的二聚体重复序列组成的单一多肽（βα2）。表达βα2多肽的COS1细胞的86Rb+外流很小，但通过补充β单体可恢复。这些结果表明，当α亚基和β亚基以1:1的摩尔比共表达时，KATP通道的活性得到优化。由于内向整流钾离子通道被认为以同四聚体或异四聚体形式发挥作用，这表明KATP通道作为一种多聚体蛋白发挥作用，很可能是由Kir6.2亚基的四聚体和SUR1亚基的四聚体组成的异八聚体。
