Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
J Am Chem Soc. 2013 Feb 13;135(6):2172-80. doi: 10.1021/ja307275v. Epub 2013 Feb 4.
The anesthetic propofol inhibits the currents of the homopentameric ligand-gated ion channel GLIC, yet the crystal structure of GLIC with five propofol molecules bound symmetrically shows an open-channel conformation. To address this dilemma and determine if the symmetry of propofol binding sites affects the channel conformational transition, we performed a total of 1.5 μs of molecular dynamics simulations for different GLIC systems with propofol occupancies of 0, 1, 2, 3, and 5. GLIC without propofol binding or with five propofol molecules bound symmetrically, showed similar channel conformation and hydration status over multiple replicates of 100-ns simulations. In contrast, asymmetric binding to one, two or three equivalent sites in different subunits accelerated the channel dehydration, increased the conformational heterogeneity of the pore-lining TM2 helices, and shifted the lateral and radial tilting angles of TM2 toward a closed-channel conformation. The results differentiate two groups of systems based on the propofol binding symmetry. The difference between symmetric and asymmetric groups is correlated with the variance in the propofol-binding cavity adjacent to the hydrophobic gate and the force imposed by the bound propofol. Asymmetrically bound propofol produced greater variance in the cavity size that could further elevate the conformation heterogeneity. The force trajectory generated by propofol in each subunit over the course of a simulation exhibits an ellipsoidal shape, which has the larger component tangential to the pore. Asymmetric propofol binding creates an unbalanced force that expedites the channel conformation transitions. The findings from this study not only suggest that asymmetric binding underlies the propofol functional inhibition of GLIC, but also advocate for the role of symmetry breaking in facilitating channel conformational transitions.
麻醉药异丙酚抑制同五聚体配体门控离子通道 GLIC 的电流，但与五个异丙酚分子对称结合的 GLIC 的晶体结构显示出开放通道构象。为了解决这个难题并确定异丙酚结合位点的对称性是否影响通道构象转变，我们对具有不同异丙酚占有率（0、1、2、3 和 5）的不同 GLIC 系统进行了总共 1.5 μs 的分子动力学模拟。没有异丙酚结合或与五个异丙酚分子对称结合的 GLIC 在 100-ns 模拟的多次重复中显示出相似的通道构象和水合状态。相比之下，不对称地结合到不同亚基中的一个、两个或三个等效位点加速了通道去水合作用，增加了孔衬 TM2 螺旋的构象异质性，并将 TM2 的侧向和径向倾斜角度向关闭通道构象移动。结果根据异丙酚结合对称性将两组系统区分开来。对称组和不对称组之间的差异与相邻疏水性门的异丙酚结合腔的方差以及结合的异丙酚施加的力相关。不对称结合的异丙酚在腔尺寸上产生更大的方差，这可能进一步增加构象异质性。在模拟过程中，每个亚基中异丙酚产生的力轨迹呈椭圆形，其较大的分量切向于孔。不对称的异丙酚结合会产生不平衡的力，从而加速通道构象转变。这项研究的结果不仅表明不对称结合是异丙酚抑制 GLIC 功能的基础，还主张对称性破缺在促进通道构象转变中的作用。
