ION CHANNEL PROTEINS IN MEMBRANES

我们的研究集中在流感-A M2蛋白，一个小的 同源四聚体电压门控离子通道。 每个单体是97个氨基 的长度，并含有一个跨膜（TM）结构域的19 残基 该通道在输送质子方面非常有效， 筛选出其他类型的离子。 虽然没有高分辨率 迄今为止，M2结构数据可用，最近的NMR和CD 对磷脂双层中这种蛋白质的研究有力地表明， TM区是α-螺旋的，并具有四级结构， 4-螺旋束 还讨论了M2的通道门控机制。 目前未知。 有两个主要假设关于门控 质子 人们认为，形成一个水线通过 通道和这种结构转移质子的能力 通过渠道。 第二个假设是基于质子 四个组氨酸残基介导的穿梭机制 形成门。 我们在这项研究中的目的是阐明 M2的门控机制，并证明一个 水-磷脂双层膜中M2分子结构模型 系统 我们进行了几次分子动力学模拟， 每个都由至少一纳秒长的轨迹组成。 每个 模拟对应于不同的质子化状态的 门中的组氨酸残基。 未质子化的单一 质子化的形式参与质子穿梭机制被发现 在整个轨道上保持稳定 而且 水分子在通道内的取向有助于 有效的质子转移。 与此相反，这四种形式 组氨酸残基被质子化，这是水线中所需的 在400 - 700年的时间尺度上， PS. 我们的结果表明，质子穿梭涉及组氨酸 蛋白质的残基是质子最可能的机制 在M2通道中传输。

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.