MECHANISM OF ION TRANSPORT THROUGH MEMBRANE CHANNELS

拟议研究的目标是了解钠的化学基础 和钾穿过生物膜的通量。 问题将是 使用三种类型的细菌来源的通道形成分子进行处理： cidin A、B 和 C 作为二聚体结合形成跨膜通道； (2) 各种化学修饰的类似物，包括共价偶联的同源和 异二聚体，这些相同的短杆菌肽也形成活性通道，但是 与天然分子不同的寿命和/或离子传输速率；和 (3)一种较大的蛋白质，最近发现的El型大肠杆菌素之一 在大肠杆菌膜中形成电压依赖性钠/钾通道 在人工脂质双层中。 研究此类分子的目的 是建立指导所有此类行动可能模式的原则 生物系统中的通道形成蛋白。 结果将表明 膜中离子泵和门作用的分子基础，其中 直接影响 (a) 细胞控制其离子组成的能力， 跨膜电位和渗透压，以及（b）神经传导 高等动物的冲动。 我们之前的工作描述了伴随着构象变化 阳离子与短杆菌肽 A、B 和 C 结合。中子衍射的组合 X射线衍射被用来进一步检查这些结构， 包括使用同晶氘氢取代相 单晶中子衍射中的反射。 此外，传导 具有多种半合成短杆菌肽A类似物的特性，其中氨基 具有不同大小和极性的侧链的酸已被取代 N-末端，正在接受检查。

The goal of the proposed research is to understand the chemical basis for sodium and potassium fluxes across biological membranes. The questions will be approached using three types of channel-forming molecules of bacterial origin: cidins A, B, and C which associate as dimers to form transmembrane channels; (2) various chemically modified analogues includng covalently coupled homo-and heterodimers, of these same gramicidins which also form active channels, but of different lifetimes and/or ion transport rates from the native molecules; and (3) a larger protein, one of the type El colicins which have recently been shown to form voltage-dependent sodium/potassium channels in the E. coli membrane and in artificial lipid bilayers. The purpose in studying these type of molecules is to establish principles governing possible modes of action of all such channel-forming proteins in biological systems. The results will indicate the molecular basis for the action of ion pumps and gates in membranes, which in turn directly affect (a) a cell's ability to control its ionic composition, transmembrane potential and osmotic pressure, and (b) the conduction of nerve impulses in higher animals. Our previous work has characterized a conformational change which accompanies cation binding to gramicidins A, B, and C. A combination of neutron diffraction and x-ray diffraction are being used to further examine these structures, including the use of isomorphous deuterium-hydrogen substitution to phase reflections in single-crystal neutron diffraction. In addition, the conducting properties of a variety of semisynthetic gramicidin A analogues, in which amino acids having side chains of varying size and polarity have been substituted at the N-terminal, are being examined.