Forrest L R, Kukol A, Arkin I T, Tieleman D P, Sansom M S
Laboratory of Molecular Biophysics, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, England.
Biophys J. 2000 Jan;78(1):55-69. doi: 10.1016/s0006-3495(00)76572-6.
The M2 protein of influenza A virus forms homotetrameric helix bundles, which function as proton-selective channels. The native form of the protein is 97 residues long, although peptides representing the transmembrane section display ion channel activity, which (like the native channel) is blocked by the antiviral drug amantadine. As a small ion channel, M2 may provide useful insights into more complex channel systems. Models of tetrameric bundles of helices containing either 18 or 22 residues have been simulated while embedded in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphatidylcholine bilayer. Several different starting models have been used. These suggest that the simulation results, at least on a nanosecond time scale, are sensitive to the exact starting structure. Electrostatics calculations carried out on a ring of four ionizable aspartate residues at the N-terminal mouth of the channel suggest that at any one time, only one will be in a charged state. Helix bundle models were mostly stable over the duration of the simulation, and their helices remained tilted relative to the bilayer normal. The M2 helix bundles form closed channels that undergo breathing motions, alternating between a tetramer and a dimer-of-dimers structure. Under these conditions either the channel forms a pocket of trapped waters or it contains a column of waters broken predominantly at the C-terminal mouth of the pore. These waters exhibit restricted motion in the pore and are effectively "frozen" in a way similar to those seen in previous simulations of a proton channel formed by a four-helix bundle of a synthetic leucine-serine peptide (, Biophys. J. 77:2400-2410).
甲型流感病毒的M2蛋白形成同源四聚体螺旋束，其作为质子选择性通道发挥作用。该蛋白的天然形式有97个氨基酸残基长，尽管代表跨膜部分的肽段显示出离子通道活性，且这种活性（如同天然通道）会被抗病毒药物金刚烷胺阻断。作为一个小离子通道，M2可能为更复杂的通道系统提供有用的见解。含有18或22个残基的螺旋四聚体束模型已在完全水合的1-棕榈酰-2-油酰-sn-甘油-3-磷脂酰胆碱双层中进行模拟。使用了几种不同的起始模型。这些表明，至少在纳秒时间尺度上，模拟结果对精确的起始结构敏感。在通道N端开口处由四个可电离天冬氨酸残基组成的环上进行的静电计算表明，在任何时刻，只有一个会处于带电状态。螺旋束模型在模拟过程中大多是稳定的，其螺旋相对于双层法线保持倾斜。M2螺旋束形成经历呼吸运动的封闭通道，在四聚体和二聚体-二聚体结构之间交替。在这些条件下，通道要么形成一个截留水的口袋，要么包含一列主要在孔的C端开口处断开的水。这些水在孔中表现出受限的运动，并以类似于先前对由合成亮氨酸-丝氨酸肽的四螺旋束形成的质子通道的模拟中所观察到的方式被有效地“冻结”。
