Structures of membrane proteins have been challenging to solve by any structural technique. We are developing solution NMR spectroscopy as a tool to study the structure and dynamics of membrane proteins, including bacterial outer membrane porins. This class of membrane proteins has proven particularly beneficial for these studies because (i) a larger chemical shift dispersion of residues is observed in β-sheets than in α-helices and (ii) much larger numbers of long-range NOEs can be observed in β-sheet vs. α-helical membrane proteins. Progress in this area will be illustrated with the small ion pore OmpA [1]. The gating of the OmpA ion channel has been studied by electrophysiological and thermodynamic approaches [2] and attempts to correlate these findings with dynamical properties of the protein will be illustrated [3]. Structural refinements can be obtained by including residual dipolar couplings and paramagnetic relaxation enhancements [4]. The methods have also been extended to solving the solution structure of the 33 kDa pH-gated porin OmpG embedded in a protein/DPC complex estimated to be about 80-90 kDa [5]. References: 1. Arora, A., Abildgaard, F., Bushweller, J.H., and Tamm, L.K. (2001) Structure of the outer membrane protein A transmembrane domain in detergent micelles by NMR spectroscopy. Nature Struct. Biol. 8:334-338. 2. Hong, H., Szabo, G., and Tamm, L.K. (2006) Electrostatic side-chain couplings in the gating of the OmpA ion channel suggest a mechanism for pore opening. Nature Chem. Biol. 11:627-635 3. Liang, B., Arora, A., and Tamm, L.K. (2010) Fast-time scale dynamics of outer membrane protein A by extended model-free analysis of NMR relaxation data. (Special issue: dynamics of membrane proteins by NMR) Biochim. Biophys. Acta 1798:68-76. 4. Liang, B., Bushweller, J.H., and Tamm, L.K. (2006) Site-directed parallel spin-labeling and paramagnetic relaxation enhancement in structure determination of membrane proteins by solution NMR. J.A.C.S., 126:4389-439. 5. Liang, B. and Tamm, L.K. (2007) Structure of outer membrane protein G by solution NMR. PNAS 104:16140-1614