Protein-Membrane Organization and Function: Ion Channels

9313835欣顿物质通过膜的运输是生命的一种基本现象。所有生物体都被特殊的膜屏障与环境隔开，这些屏障控制着物质与周围环境的交换，并充当着电阻的角色。此外，几乎所有的生命过程都与膜功能密切相关。因此，膜功能在细胞之间和细胞内的交流中起着核心作用，在将代谢能量转化为渗透性、电性和某种程度上的机械功的过程中发挥着核心作用。在活细胞中，由于离子在细胞周围质膜两侧的分布不均匀，细胞质和细胞外介质之间存在电势差。细胞膜配备了特殊的运输机制，可以加速离子通过脂质屏障。对这些转运机制的理解对于理解某些类型的膜功能的最终目标是至关重要的。单价阳离子如Li+、Na+和K+通过细胞膜的运输在许多不同的生理过程中起着关键作用。这些过程涉及跨膜电位的维持，神经冲动沿着轴突和跨神经肌肉接头的传导，以及细胞的分化和生长。相对较少的物理技术可用于表征单价阳离子与负责阳离子运输的生物分子之间的相互作用。然而，核磁共振波谱已被证明是一种非常强大的技术，用于研究转运过程和负责转运的分子系统。核磁共振方法可用于确定通道的三维结构，确定将转运系统整合到膜中的热力学参数，确定阳离子与通道结合的热力学参数，以及测定转运过程的活化热。%所要求的资助期的目标包括使用多核多维核磁共振波谱，通过使用核磁共振确定的质子距离限制的分子动力学/模拟退火法和多肽合成来确定结构，以：(1)研究单一氨基酸取代对通道结构的影响，作为通道的膜的整合，阳离子在通道系统中的结合和运输，gricidin。目的是确定该结构与通道形成和选择性单价阳离子转运的关系；(2)获得与烟碱型乙酰胆碱受体通道相关的五聚体螺旋束中单个螺旋成分的模型膜的结构。还将研究单价阳离子结合和传输选择性。***

9313835 Hinton The transport of matter through membranes is a basic phenomenon of life. All organisms are separated from their environment by special membrane barriers which control the exchange of matter with their surroundings and act as an electrical resistor. In addition, nearly all life processes are intimately involved with membrane function. Thus, membrane functions play a central role in communication between and within cells, in the transformation of metabolic energy into osmotic, electrical, and to some extent mechanical work. In living cells an electrical potential difference exists between the cytoplasma and the extracellular medium because of the unequal distribution of ions on both sides of the plasma membrane surrounding the cell. The cell membranes are equipped with special transport mechanisms which accelerate the passage of ions across the lipid barrier. An understanding of these transport mechanisms is a vital link to the ultimate goal of the comprehension of some types of membrane function. The transport of monovalent cations, such as Li+, Na+, and K+, through cell membranes plays a key role in many different physiological processes. These processes involve the maintenance of transmembrane potential, conduction of nerve impulses down the axon and across the neuromuscular junction and the differentiation and growth of cells. There are relatively few physical techniques available for the characterization of the interaction of monovalent cations with biological molecules responsible for cation transport. However, nuclear magnetic resonance spectroscopy (NMR) has proven to be an exceptionally powerful technique for the study of the transport process and the molecular systems responsible for the transport. NMR methods may be used to determine the 3-dimensional structure of the channel, to determine the thermodynamic parameters for the integration of transport system into membranes, to determine the thermodynamic parameters for the binding of the cations to the channel and for determining the activation enthalpy for the transport process. %%% The objectives for the requested funding period involve the use of multinuclei multidimensional NMR spectroscopy, structure determination through the use of NMR determined proton distance restrained molecular dynamics/simulated annealing and peptide synthesis to: (1) study the effect of single amino acid substitution on channel structure, the integration into a membrane as a channel, cation binding and transport in the channel system, gramicidin. The objective is to determine how the structure is related to channel formation and selective monovalent cation transport; (2) to obtain the structure of the model membrane bound individual helical components of the pentameric helical bundle that is related to the nicotinic acetylcholine receptor channel. Monovalent cation binding and transport selectivity will also be investigated. ***