Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
J Am Chem Soc. 2011 Mar 30;133(12):4274-84. doi: 10.1021/ja102581n. Epub 2011 Mar 7.
The transmembrane domain of the influenza M2 protein (M2TM) forms a tetrameric proton channel important for the virus lifecycle. The proton-channel activity is inhibited by amine-containing adamantyl drugs amantadine and rimantadine, which have been shown to bind specifically to the pore of M2TM near Ser31. However, whether the polar amine points to the N- or C-terminus of the channel has not yet been determined. Elucidating the polar group direction will shed light on the mechanism by which drug binding inhibits this proton channel and will facilitate rational design of new inhibitors. In this study, we determine the polar amine direction using M2TM reconstituted in lipid bilayers as well as dodecylphosphocholine (DPC) micelles. (13)C-(2)H rotational-echo double-resonance NMR experiments of (13)C-labeled M2TM and methyl-deuterated rimantadine in lipid bilayers showed that the polar amine pointed to the C-terminus of the channel, with the methyl group close to Gly34. Solution NMR experiments of M2TM in DPC micelles indicate that drug binding causes significant chemical shift perturbations of the protein that are very similar to those seen for M2TM and M2(18-60) bound to lipid bilayers. Specific (2)H-labeling of the drugs permitted the assignment of drug-protein cross peaks, which indicate that amantadine and rimantadine bind to the pore in the same fashion as for bilayer-bound M2TM. These results strongly suggest that adamantyl inhibition of M2TM is achieved not only by direct physical occlusion of the channel, but also by perturbing the equilibrium constant of the proton-sensing residue His37. The reproduction of the pharmacologically relevant specific pore-binding site in DPC micelles, which was not observed with a different detergent, DHPC, underscores the significant influence of the detergent environment on the functional structure of this membrane protein.
流感 M2 蛋白（M2TM）的跨膜域形成四聚质子通道，对于病毒生命周期至关重要。质子通道活性被含有胺的金刚烷药物金刚烷胺和金刚乙胺抑制，这些药物已被证明特异性结合于 M2TM 蛋白位于 Ser31 附近的孔。然而，极性胺指向通道的 N 端还是 C 端尚未确定。阐明极性基团的方向将揭示药物结合抑制这种质子通道的机制，并促进新抑制剂的合理设计。在这项研究中，我们使用脂质双层和十二烷基磷酸胆碱（DPC）胶束中重建的 M2TM 来确定极性胺的方向。（13）C-（2）H 旋转回波双共振 NMR 实验显示，在脂质双层中，（13）C 标记的 M2TM 和氘代金刚烷胺的甲基与 Gly34 接近，表明极性胺指向通道的 C 端。DPC 胶束中 M2TM 的溶液 NMR 实验表明，药物结合导致蛋白质的化学位移发生显著变化，与 M2TM 和结合于脂质双层的 M2（18-60）非常相似。药物的特定（2）H 标记允许分配药物-蛋白质交叉峰，这表明金刚烷胺和金刚乙胺以与结合于脂质双层的 M2TM 相同的方式结合到孔中。这些结果强烈表明，金刚烷抑制 M2TM 不仅通过直接物理阻塞通道来实现，而且还通过干扰质子感应残基 His37 的平衡常数来实现。在不同的去污剂 DHPC 中未观察到的与药理学相关的特定孔结合位点在 DPC 胶束中的重现，突出了去污剂环境对这种膜蛋白功能结构的显著影响。
