Wischmeyer E, Döring F, Wischmeyer E, Spauschus A, Thomzig A, Veh R, Karschin A
Max-Planck-Institute for Biophysical Chemistry, Molecular Neurobiology of Signal Transduction, Göttingen, Germany.
Mol Cell Neurosci. 1997;9(3):194-206. doi: 10.1006/mcne.1997.0614.
Cardiac G protein-activated Kir (GIRK) channels may assemble as heterotetrameric polypeptides from two subunits, Kir3.1 and Kir3.4. For a functional comparison with native channels in the CNS we investigated all possible combinations of heteromeric channel formation from brain Kir3.1, Kir3.2, Kir3.3, and Kir3.4 subunits in mRNA-injected Xenopus oocytes. Analysis of macroscopic current amplitudes and channel gating kinetics indicated that individual subunits or combinations of Kir3.2, Kir3.3, and Kir3.4 formed functional channels ineffectively. Each of these subunits gave rise to prominent currents with distinct characteristics only in the presence of Kir3.1 subunits. Functional expression of concatemeric constructs between Kir3.1 and Kir3.2/3.4 subunits as well as coimmunoprecipitations with subunit-specific antibodies confirmed heteromeric channel formation. Mutational swapping between subunits of a single pore loop residue (Kir3.1F137S; Kir3.3S114F; a phenylalanine confers slow channel gating in Kir3.1 subunits) revealed that Kir3.1 subunits are an important constituent for native heteromeric channels and dominate their functional properties. However, homomeric channels from Kir3.1 subunits in vivo may not exist due to the spatial conflict of bulky phenylalanines in the pore structure.
心脏G蛋白激活的内向整流钾通道（GIRK）可能由Kir3.1和Kir3.4两个亚基组装成异源四聚体多肽。为了与中枢神经系统中的天然通道进行功能比较，我们研究了mRNA注射的非洲爪蟾卵母细胞中脑Kir3.1、Kir3.2、Kir3.3和Kir3.4亚基形成异源通道的所有可能组合。宏观电流幅度和通道门控动力学分析表明，Kir3.2、Kir3.3和Kir3.4的单个亚基或组合形成功能性通道的效率较低。只有在存在Kir3.1亚基的情况下，这些亚基中的每一个才会产生具有不同特征的显著电流。Kir3.1与Kir3.2/3.4亚基之间的串联构建体的功能表达以及与亚基特异性抗体的共免疫沉淀证实了异源通道的形成。单个孔环残基亚基之间的突变交换（Kir3.1F137S；Kir3.3S114F；苯丙氨酸在Kir3.1亚基中导致通道门控缓慢）表明，Kir3.1亚基是天然异源通道的重要组成部分，并主导其功能特性。然而，由于孔结构中庞大苯丙氨酸的空间冲突，体内Kir3.1亚基的同源通道可能不存在。
