Structure, Stability, and Function of Ion Channels and Other Membrane Proteins

Membrane proteins – receptors, ion channels, transporters, etc.  – constitute about 30% of all proteins in eukaryotic cells. Many of them are targets for current or future drugs. In order to facilitate the basic understanding of the biology of these proteins and in order to aid future rational drug design improved methods are needed to solve the structures of this class of proteins. Since membrane proteins are harder to express and handle than soluble proteins, specialized expression, solubilization, and stabilization techniques are required. Our laboratory is active in all these areas and we are particularly interested in solving structures of membrane proteins by solution NMR spectroscopy. We have solved the very first membrane protein structure that was solved by this technique in 2001, i.e. that of the outer membrane ion channel OmpA (see here for picture). We also performed dynamic, thermodynamic, and electrical channel recording experiments to delineate the gating mechanism of this ion channel. More recently in 2007, we solved the structure of the outer membrane porin OmpG by NMR spectroscopy. This is currently the largest membrane protein structure (33 kDa, 280 residues) ever solved by NMR (see here for picture). The methods that we are developing with these proteins should also be helpful to tackle more difficult projects in the future like helical receptors and ion channels that have been identified as potential drug targets.

 

Gating of OmpA ion channel

 

Recent Key Publications:

Liang B. and Tamm, L.K. (2007) Structure of outer membrane protein G by solution NMR spectrscopy. PNAS. Vol. 104 no.41:16140-16145. (Full text in PDF) (Supplement)

Hong, H., Park, S., Flores-Jiménez, R.H., Rinehart, D., and Tamm, L.K. (2007) Role of aromatic side chains in the folding and thermodynamic stability of integral membrane proteins. J.A.C.S. 129:8320-8327. (Full text in PDF) (Supplement)

Hong H., Szabo G., Tamm L.K. (2006) Electrostatic Coupling in OmpA Ion-Channal Gating Suggest a Mechanism for Pore Opening. Nature Chem. Biol. Vol.2 No.11 627-635. (Full text in PDF)

Tamm L.K., Liang B.  (2006). NMR of membrane protein in solution. Prog. in  Nuc Mag Res Spec.  Vol.48 201-210. (Full text in PDF).

Cierpicki T., Liang B., Tamm L.K., Bushweller J.H..  (2006). Increasing teh Accuracy of Solution NMR Structures of Membrane Proteins by Application of Residual Dipolar Coupling. High-Resolution Structure of Outer Membrane Protein A.. J. Am Chem. Soc  Vol.128 No.21 6947-6951. (Full text in PDF).

Liang B., Bushweller J.H., Tamm L.K. (2006). Site-Directed Parallel Spin-Labeling and Paramagnetic Relaxation Enhancement in Structure Determination of Membrane Proteins by Solution NMR Spectroscopy. J. Am Chem. Soc  Vol.128 No.13 4389-4397. (Full text in PDF).

Hong, H., Patel D.R., Tamm L.K. and Berg B.V.D. (2006). The Outer Membrane Protein OmpW Forms an Eight-stranded β-Barrel with a Hydrophobic Channel. Jour. of Biol Chem. Vol. 281 No.11: 7568-7577. (Full text in PDF).

Tamm, L.K., H. Hong, and B. Liang (2004). Folding and assembly of beta-barrel membrane proteins. (Review) Biochim. Biophys. Acta. 1666: 250-263. (Full text in PDF).

Hong, H. and L.K. Tamm (2004). Elastic coupling of integral membrane protein stability to lipid bilayer forces. Proc. Nat. Acad. Sci. 101: 4065-4070 (Full text in PDF). Commentary by Dr. James Bowie (PDF).

Tamm, L.K., F. Abildgaard, A. Arora, H. Blad, and J.H. Bushweller (2003). Structure, dynamics and function of the outer membrane protein A (OmpA) and influenza hemagglutinin fusion domain in detergent micelles by solution NMR. (Minireview) FEBS Lett. 555: 139-143. (Full text in PDF)

Kleinschmidt, J.H. and L.K. Tamm (2002). Secondary and tertiary structure formation of the beta-barrel membrane protein OmpA is synchronized and depends on membrane thickness. J. Mol. Biol. 324: 319-330. (Full text in PDF)

Kleinschmidt, J.H. and L.K. Tamm (2002). Structural transitions in short-chain lipid assemblies studied by P(31)-NMR spectroscopy. Biophys. J. 83: 994-1003. (Full text in PDF)

Arora, A. and L.K. Tamm (2001). Biophysical approaches to membrane protein structure determination. (Review) Curr. Opin. Struct. Biol. 11: 540-547. (Full text in PDF)

Tamm, L.K., A. Arora, and J.H. Kleinschmidt (2001). Structure and assembly of beta-barrel membrane proteins. (Review) J. Biol. Chem. 276: 32399-32402. (Full text in PDF)

Arora, A., A. Frits, J.H. Bushweller, and L.K. Tamm (2001). Structure of outer membrane protein A transmembrane domain by NMR spectroscopy. Nature Struct. Biol. 8: 334-338. (Full text in PDF)

Arora, A., D. Rinehart, G. Szabo, and L.K. Tamm (2000). Refolded outer membrane protein A of Escherichia coli forms ion channels with two conductance states in planar bilayers. J. Biol. Chem. 275:1594-1600. (Full text in PDF)

Kleinschmidt, J.H., M. Wiener, and L.K. Tamm (1999). Outer membrane protein A of E. coli folds into detergent micelles, but not in the presence of monomeric detergent. Protein Sci. 8:2065-2071. (Full text in PDF)

Kleinschmidt, J.H. and L.K. Tamm (1999). Time-resolved distance determination by tryptophan fluorescence quenching (TDFQ): Probing intermediates in membrane protein folding. Biochemistry 38: 4996-5005. (Full text in PDF)

Kleinschmidt, J.H., T. den Blaauwen, A.J.M. Driessen, and L.K. Tamm (1999). Outer membrane protein A of Escherichia coli inserts and folds into lipid bilayers by a concerted mechanism. Biochemistry 38: 5006-5016. (Full text in PDF)

Kleinschmidt, J. and L.K. Tamm (1996). Folding intermediates of a beta-barrel membrane protein. Kinetic evidence for a multi-step membrane insertion mechanism. (accelerated publication) Biochemistry. 35:12993-13000. (Full text in PDF)

Rodionova, N.A., S.A. Tatulian, T. Surrey, F. Jähnig, and L.K. Tamm (1995). Characterization of two membrane-bound forms of OmpA. Biochemistry. 34:1921-1929.

Tamm, L.K. (1994) Physical studies of peptide-bilayer interactions. In Membrane Protein Structure, Experimental Approaches. S.H. White, ed., Oxford University Press, pp. 281-313.