Membrane proteins, many of which are important drug targets, constitute about 30 % of the human proteome. While structural genomics initiatives are well underway to solve the high-resolution structures of scores of soluble proteins, technologies have not advanced far enough to undertake a similar massive parallel approach to solve the structures of a very large number of integral membrane proteins. One bottleneck concerns difficulties with the successful refolding of membrane proteins. We have recently made substantial progress in this area by achieving reversible refolding conditions and elucidating folding mechanisms of beta-barrel membrane proteins, which are present in the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. We have also recently solved the structure of OmpA by solution NMR. This was the first structure of a larger integral membrane protein that has been solved by this method. Building on this success, we propose to further elucidate mechanisms of membrane protein folding and the energetics of membrane protein stability using OmpA as a model and to extend our experience to other integral membrane proteins, namely the porin OmpG, and the isoprenylcysteine carboxyl methyltransferase (ICMT) Ste14p, which shares high sequence homology with the human ICMT that post-translationally modifies Ras. We also propose to further refine solution NMR methods for solving structures and elucidating the dynamics of membrane proteins in detergent/lipid micelles and to apply these methods to OmpG and Ste14p, whose structures and dynamical properties are not yet known.
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