ION CHANNEL PROTEINS IN MEMBRANES

我们的研究重点是流感-A M2蛋白，一种小的 同四聚体，电压门控离子通道。每个单体含有97个氨基 含有一个跨膜(TM)结构域，长度为19 残留物。这个通道在传输质子和质子方面非常有效 屏蔽掉其他类型的离子。虽然分辨率不高 M2的结构数据是最新的，最近的核磁共振和CD 对磷脂双层中这种蛋白质的研究强烈表明， TM区域是α螺旋的，并且具有四级结构 4螺旋束。M2的通道选通机制也是 目前尚不清楚。有两个关于门控的主要假设 质子。我们可以考虑一下水线的形成。 通道和这种结构转移质子的能力 通过海峡。第二种假设是基于一个质子 腔内四个组氨酸残基介导的穿梭机制 形成了大门。我们在这项研究中的目的是阐明 M2的门控机制，并证明了一种 显式水-磷脂双层膜中M2的结构模型 系统。我们已经进行了几次分子动力学模拟， 每一个都由至少一纳秒长的轨道组成。每个人 模拟对应于不同的质子化状态 大门里有组氨酸残留物。未质子化和单质子化 发现了与质子穿梭机制有关的质子化形式 在整个弹道上保持稳定。此外， 水分子在通道内的定向有利于 有效的质子转移。相比之下，这四个人的形式 组氨酸残基是质子化的，需要在水线上 机制，在400-700的时间尺度上是不稳定和分离的 PS.我们的结果表明，质子穿梭涉及组氨酸 蛋白质残基是质子最有可能的作用机制 M2通道中的传输。

Our research focuses on the Influenza-A M2 protein, a small homotetrameric, voltage-gated ion channel. Each monomer is 97 amino acids in length, and contains a single transmembrane (TM) domain of 19 residues. This channel is very effective in transporting protons and screens out other types of ions. Although no high resolution structural data for M2 are available to date, recent NMR and CD studies of this protein in phospholipid bilayers strongly suggest that the TM region is alpha-helical and has the quaternary structure of a 4-helix bundle. The mechanisms of channel gating by M2 is also currently unknown. There are two main hypotheses regarding gating of protons. One considers the formation of a water wire through the channel and the ability of such a structure to transfer protons through the channel. The second hypothesis is based on a proton shuttle mechanism mediated by four intraluminal histidine residues forming the gate. Our aim in this study has been to elucidate the gating mechanism of M2, and to demonstrate the stability of a structural model of M2 in an explicit water-phospholipid bilayer system. We have performed several molecular dynamics simulations, each consisting of a trajectory at least one nanosecond long. Each simulation corresponded to a different protonation state of the histidine residues in the gate. The unprotonated and single protonated forms involved in the proton shuttle mechanism were found to be stable over the full length of the trajectory. Furthermore, the orientation of water molecules inside the channel was conducive to effective proton transfer. In contrast, the form in which all four histidine residues are protonated, required in the water-wire mechanism, was unstable and disassociated on a timescale of 400 - 700 ps. Our results demonstrate that proton shuttle involving histidine residues of the protein is the most likely mechanism of proton transport in the M2 channel.