Protein-Membrane Organization and Function: Ion Channels

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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. ***