Rapedius Markus, Paynter Jennifer J, Fowler Philip W, Shang Lijun, Sansom Mark S P, Tucker Stephen J, Baukrowitz Thomas
Institute of Physiology II, Friedrich Schiller University, Jena, Germany.
Channels (Austin). 2007 Sep-Oct;1(5):327-30. doi: 10.4161/chan.5176. Epub 2007 Oct 15.
Inhibition by intracellular H(+) (pH gating) and activation by phosphoinositides such as PIP(2) (PIP(2)-gating) are key regulatory mechanisms in the physiology of inwardly-rectifying potassium (Kir) channels. Our recent findings suggest that PIP(2) gating and pH gating are controlled by an intra-subunit H-bond at the helix-bundle crossing between a lysine in TM1 and a backbone carbonyl group in TM2. This interaction only occurs in the closed state and channel opening requires this H-bond to be broken, thereby influencing the kinetics of PIP(2) and pH gating in Kir channels. In this addendum, we explore the role of H-bonding in heteromeric Kir4.1/Kir5.1 channels. Kir5.1 subunits do not possess a TM1 lysine. However, homology modelling and molecular dynamics simulations demonstrate that the TM1 lysine in Kir4.1 is capable of H-bonding at the helix-bundle crossing. Consistent with this, the rates of pH and PIP2 gating in Kir4.1/Kir5.1 channels (two H-bonds) were intermediate between those of wild-type homomeric Kir4.1 (four H-bonds) and Kir4.1(K67M) channels (no H-bonds) suggesting that the number of H-bonds in the tetrameric channel complex determines the gating kinetics. Furthermore, in heteromeric Kir4.1(K67M)/Kir5.1 channels, where the two remaining H-bonds are disrupted, we found that the gating kinetics were similar to Kir4.1(K67M) homomeric channels despite the fact that these two channels differ considerably in their PIP(2) affinities. This indicates that Kir channel PIP(2) affinity has little impact on either the PIP(2) or pH gating kinetics.
细胞内H⁺抑制（pH门控）和磷脂酰肌醇（如PIP₂）激活（PIP₂门控）是内向整流钾通道（Kir）生理学中的关键调节机制。我们最近的研究结果表明，PIP₂门控和pH门控受亚基内TM1中赖氨酸与TM2中主链羰基之间螺旋束交叉处的氢键控制。这种相互作用仅在关闭状态下发生，通道开放需要该氢键断裂，从而影响Kir通道中PIP₂和pH门控的动力学。在本附录中，我们探讨了氢键在异源Kir4.1/Kir5.1通道中的作用。Kir5.1亚基不具有TM1赖氨酸。然而，同源建模和分子动力学模拟表明，Kir4.1中的TM1赖氨酸能够在螺旋束交叉处形成氢键。与此一致的是，Kir4.1/Kir5.1通道（两个氢键）中的pH和PIP₂门控速率介于野生型同源Kir4.1（四个氢键）和Kir4.1(K67M)通道（无氢键）之间，这表明四聚体通道复合物中氢键的数量决定了门控动力学。此外，在异源Kir4.1(K67M)/Kir5.1通道中，其余两个氢键被破坏，我们发现尽管这两个通道的PIP₂亲和力有很大差异，但门控动力学与Kir4.1(K67M)同源通道相似。这表明Kir通道的PIP₂亲和力对PIP₂或pH门控动力学几乎没有影响。
