Structures, Dynamics, and Functions of Membrane Proteins

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7. Project Summary Membrane proteins are important targets for structure determination. One quarter of the proteins in the human genome are membrane proteins, and the majority of drug targets are membrane proteins. However, both structure determination and dynamics characterization of membrane proteins have lagged because of technological difficulties resulting largely from the phospholipid environment in which the proteins reside; it is highly asymmetric with hydrophobic and hydrophilic components, and it immobilizes the proteins. Consequently, our overarching goal is to develop new and more powerful methods for determining the structures of membrane proteins. This is an essential first step in revealing the bases of their functions. Although considerable progress has been made using solution NMR, X-ray crystallography, and electron microscopy, this has been at the potential cost of distorting the structures through the use of detergent environments and cryogenic temperatures for the protein samples. None of the proteins that we are studying have been crystallized. Thus, the technology gap that we seek to fill is well defined. Innovative features of the research plan include its scientific breadth, which ranges from molecular biology to structure calculations. Several smaller membrane proteins will be used for methods development, including Vpu from HIV-1, p7 from HCV, and mercury transport proteins from the bacterial mercury detoxifications system. They serve the dual purposes of posing interesting biochemical functional questions and serving as tractable systems for developing methods of determining the structures and describing the dynamics of larger membrane proteins, such as our principal target of G-protein coupled receptors (GPCRs). At the conclusion of the research plan, we expect to be able to describe the functions of chemokine receptors. These studies will involve the structures and dynamics of the monomeric proteins, protein-protein interactions, and conformational changes in the proteins. NMR is unique in its ability to characterize global and local dynamics of proteins. Thus, the findings will be highly complementary to parallel studied by x-ray crystallography and electron microscopy. Moreover, NMR is capable of describing structure, dynamics, and interactions of the proteins in their phospholipid bilayer environment under physiological conditions.