Huang C L, Jan Y N, Jan L Y
Department of Physiology, the University of California at San Francisco, 94143-0724, USA.
FEBS Lett. 1997 Apr 1;405(3):291-8. doi: 10.1016/s0014-5793(97)00197-x.
We have previously shown that direct binding of the betagamma subunit of G protein (G betagamma) to both the N-terminal domain and the C-terminal domain of a cloned G protein-gated inward-rectifying K+ channel subunit, GIRK1, is important for channel activation. We have now further localized the G betagamma binding region in the N-terminal domain of GIRK1 to amino acids 34-86 and the G betagamma binding region in the C-terminal domain of GIRK1 to two separate fragments of amino acids 318-374 and amino acids 390-462. Of the four cloned mammalian GIRK subunits, GIRK1-4, GIRK1 and 4 form heteromeric K+ channels in the heart and similar channels in the brain include heteromultimers of GIRK1 and 2, and possibly other GIRK homomultimers and heteromultimers. We found that the N-terminal and the C-terminal domains of all four GIRKs bound G betagamma. The G betagamma binding activities for the C-terminal domains of GIRK2-4 were lower than that for the C-terminal domain of GIRK1. The higher G betagamma binding activity for the C-terminal domain of GIRK1 is due to amino acids 390-462 which are unique to GIRK1. We also found that the N-terminal and C-terminal domains of GIRKs interacted with each other, and the N-terminal domain of either GIRK1 or GIRK4 together with the C-terminal domain of GIRK1 exhibited much enhanced binding of G betagamma. These results are consistent with the idea that the N- and C-terminal domains of the cardiac G protein-gated K+ channel subunits may interact with each other to form higher affinity binding site(s) for G betagamma.
我们之前已经表明，G蛋白的βγ亚基（Gβγ）与克隆的G蛋白门控内向整流钾通道亚基GIRK1的N端结构域和C端结构域直接结合，对通道激活很重要。我们现在进一步将GIRK1的N端结构域中的Gβγ结合区域定位到氨基酸34 - 86，将GIRK1的C端结构域中的Gβγ结合区域定位到两个单独的氨基酸片段，即318 - 374和390 - 462。在四个克隆的哺乳动物GIRK亚基GIRK1 - 4中，GIRK1和4在心脏中形成异源多聚体钾通道，大脑中类似的通道包括GIRK1和2的异源多聚体，可能还有其他GIRK同源多聚体和异源多聚体。我们发现所有四个GIRK的N端和C端结构域都能结合Gβγ。GIRK2 - 4的C端结构域的Gβγ结合活性低于GIRK1的C端结构域。GIRK1的C端结构域具有较高的Gβγ结合活性是由于氨基酸390 - 462，这是GIRK1所特有的。我们还发现GIRK的N端和C端结构域相互作用，并且GIRK1或GIRK4的N端结构域与GIRK1的C端结构域一起表现出对Gβγ的结合显著增强。这些结果与心脏G蛋白门控钾通道亚基的N端和C端结构域可能相互作用以形成对Gβγ具有更高亲和力的结合位点这一观点一致。
