CRYSTALLOGRAPHIC ANALYSES OF (MOSTLY) ELECTRON TRANSFER PROTEINS

机械敏感性离子通道在转导中起着关键作用， 将细胞膜上的物理应力转化为电化学 反应 MscL家族的机械敏感性通道广泛地 分布于原核生物中，并可能参与调节 细胞内渗透压的变化。 为了更好 了解这些通道功能的结构基础，我们 已经确定了分枝杆菌MscL同源物的结构 结核病的X射线晶体学3.5 E分辨率， 衍射数据主要在SSRL收集。 该信道 组织为同五聚体，每个亚基含有两个 跨膜的？螺旋和第三个细胞质螺旋。 从 细胞外侧，一个直径约18 E的充满水的开口通向 一个漏斗状的孔，内衬亲水性残基，在 细胞质侧到封闭的疏水顶端， 通道门。 这种结构可以作为其他建筑的模式。 机械敏感通道，以及更广泛的五聚体 配体门控离子通道，例如烟碱乙酰胆碱 受体的

Mechanosensitive ion channels play a critical role in transducing physical stresses at the cell membrane into an electrochemical response. The MscL family of mechanosensitive channels is widely distributed among prokaryotes, and may participate in the regulation of osmotic pressure changes within the cell. In an effort to better understand the structural basis for the function of these channels, we have determined the structure of the MscL homologue from Mycobacterium tuberculosis by x-ray crystallography to 3.5 E resolution using diffraction data collected primarily at SSRL. This channel is organized as a homopentamer with each subunit containing two transmembrane ?-helices and a third cytoplasmic ?-helix. From the extracellular side, an ~18 E diameter water-filled opening leads into a funnel-shaped pore lined with hydrophilic residues which narrows at the cytoplasmic side to an occluded hydrophobic apex that may act as the channel gate. This structure may serve as a model for other mechanosensitive channels, as well as the broader class of pentameric ligand-gated ion channels exemplified by the nicotinic acetylcholine receptor.