University of Chicago, IL, USA.
Channels (Austin). 2011 Nov-Dec;5(6):482-8. doi: 10.4161/chan.5.6.18354. Epub 2011 Nov 1.
Structure of the Ca channel open pore is unlikely to be the same as that of the K channel because Ca channels do not contain the hinge residues Gly or Pro. The Ca channel does not have a wide entry into the inner pore, as is found in K channels. First we sought to simulate the open state of the Ca channel by modeling forced opening of the KcsA channel using a procedure of restrained minimization with distance constraints at the level of the α-helical bundle, corresponding to segments Thr-107-Val-115. This produced an intermediate open state, which was populated by amino acid residues of Ca channels and then successively optimized until the opening of the pore reached a diameter of about 10 Å, large enough to allow verapamil to enter and block the Ca channel from inside. Although this approach produced a sterically plausible structure, it was in significant disagreement with the MTSET accessibility data for single cysteine mutations of S6 segments of the P/Q channel(1) that do not fit with an α-helical pattern. Last we explored the idea that the four S6 segments of Ca channels may contain intra-molecular deformations that lead to reorientation of its side chains. After introduction of π-bulges, the model agreed with the MTSET accessibility data. MTSET modification of a cysteine at the C-end of only one S6 could produce physical occlusion and block of the inner pore of the open Ca channel, as observed experimentally, and as expected if the pore opening is narrower than that of K channels.
钙通道的开放孔结构不太可能与钾通道的结构相同，因为钙通道不包含铰链残基甘氨酸或脯氨酸。钙通道没有像钾通道那样在内腔中有一个宽阔的入口。首先，我们试图通过使用距离约束限制的约束最小化程序来模拟 KcsA 通道的强制开放，来模拟钙通道的开放状态，该程序的约束位于α-螺旋束的水平，对应于 Thr-107-Val-115 片段。这产生了一个中间开放状态，由钙通道的氨基酸残基填充，然后依次进行优化，直到孔的开口达到约 10Å 的直径，大到足以允许维拉帕米进入并从内部阻断钙通道。尽管这种方法产生了一种空间上合理的结构，但它与 P/Q 通道 S6 片段的单个半胱氨酸突变的 MTSET 可及性数据（1）存在显著分歧，这些数据不符合α-螺旋模式。最后，我们探讨了钙通道的四个 S6 片段可能包含导致其侧链重排的分子内变形的想法。引入π-凸起后，该模型与 MTSET 可及性数据一致。在一个 S6 的 C 末端引入半胱氨酸的 MTSET 修饰可以产生物理阻塞和开放钙通道的内孔阻塞，这与实验观察到的情况一致，如果孔的开口比钾通道窄，则这是可以预期的。
