Department of Physics and Astronomy, University of California, Irvine, California, USA.
Biophys J. 2010 Jun 16;98(12):2857-66. doi: 10.1016/j.bpj.2010.03.031.
Voltage-sensing domains (VSDs) of voltage-gated potassium (Kv) channels undergo a series of conformational changes upon membrane depolarization, from a down state when the channel is at rest to an up state, all of which lead to the opening of the channel pore. The crystal structures reported to date reveal the pore in an open state and the VSDs in an up state. To gain insights into the structure of the down state, we used a set of experiment-based restraints to generate a model of the down state of the KvAP VSD using molecular-dynamics simulations of the VSD in a lipid bilayer in excess water. The equilibrated VSD configuration is consistent with the biotin-avidin accessibility and internal salt-bridge data used to generate it, and with additional biotin-avidin accessibility data. In the model, both the S3b and S4 segments are displaced approximately 10 A toward the intracellular side with respect to the up-state configuration, but they do not move as a rigid body. Arginine side chains that carry the majority of the gating charge also make large excursions between the up and down states. In both states, arginines interact with water and participate in salt bridges with acidic residues and lipid phosphate groups. An important feature that emerges from the down-state model is that the N-terminal half of the S4 segment adopts a 3(10)-helical conformation, which appears to be necessary to satisfy a complex salt-bridge network.
电压门控钾 (Kv) 通道的电压感应结构域 (VSD) 在膜去极化时经历一系列构象变化，从通道静止时的向下状态到向上状态，所有这些变化都导致通道孔的打开。迄今为止报道的晶体结构显示孔处于开放状态，VSD 处于向上状态。为了深入了解向下状态的结构，我们使用了一组基于实验的约束条件，使用过量水中双层脂质中的 VSD 的分子动力学模拟生成 KvAP VSD 向下状态的模型。平衡的 VSD 构象与用于生成它的生物素 - 亲和素可及性和内部盐桥数据以及其他生物素 - 亲和素可及性数据一致。在该模型中，相对于向上状态构型，S3b 和 S4 片段都向细胞内方向位移约 10 Å，但它们不是作为刚体移动。承载大部分门控电荷的精氨酸侧链也在向上和向下状态之间进行大的偏移。在两种状态下，精氨酸与水相互作用，并与酸性残基和脂质磷酸基团形成盐桥。从向下状态模型中出现的一个重要特征是 S4 片段的 N 端半段采用 3(10)-螺旋构象，这似乎是满足复杂盐桥网络所必需的。
