Jason Schnell
Structure and regulation of ion channels and membrane-bound receptors
Co-workers: Jolyon Claridge, Barbara Sladek
Membrane-inserted ion channel proteins provide controlled and efficient transfer of ions across cell membranes, and are directly involved in a wide range of cellular processes such as apoptosis and synaptic transmission. As a consequence, abnormal channel activity can be at the root of seemingly disparate diseases such as cystic fibrosis, heart disease, and epilepsy. Ion channels are frequently also important for the survival or toxicity of pathogens. For these reasons, our lab is interested in understanding the molecular details of ion channel function, including the impact of mutations and small-molecule binding on channel gating, and how regulatory protein interactions modulate channel activity. Some of the specific projects in the lab focus on understanding antiviral drug resistance in the M2 channel from Influenza A, and the structure, gating, and noncompetitive inhibition of ionotropic glutamate receptors.
In addition to channels for ion transport, cells also depend on information transport via membrane-inserted ligand receptors. However, new methods for studying membrane receptors at atomic resolution are needed.
For example, diffusable-ligand, G protein-coupled receptors have been difficult to study by traditional methods that require crystallization, partly because of the need for their solubilization in lipids and detergents, but also because conformational dynamics are inherent to their function. Since, the upper size limit of proteins that can be studied by solution NMR now is above 30 kD, several classes of medically relevant membrane receptors should be amenable to atomic-resolution studies in solution, which would greatly facilitate understanding the molecular details of the conformational switching required for signal transduction. With this goal in mind, our lab is developing new techniques in sample preparation, isotopic labeling, and structural restraint measurement.
A central technique in the lab is solution NMR, which has the ability to rapidly detect the sites of intermolecular interactions and associated conformational changes. In addition, one can determine the rate of interconversion and the relative populations of conformational substates, which are likely to be important in ion channel gating and signal transduction. The results of spectroscopic experiments are interpreted in the context of in vitro functional studies (for example, liposomal flux assays).
Publications
- Pielak, R. M., Schnell, J. R. and Chou, J. J. (2009). Mechanism of Drug Inhibition and Drug Resistance of Influenza A M2 Channel. Proc. Natl. Acad. Sci. USA, (in press)
- Schnell, J. R. and Chou, J. J. (2008). Structure and Mechanism of the M2 Proton Channel of Influenza A Virus. Nature, 451, 591-595
- Call, M. E., Schnell, J. R., Xu, C., Lutz, R. A., Chou, J. J. and Wucherpfennig, K. W. (2006). The Structure of the zz Transmembrane Dimer Reveals Polar Features Essential for Dimerization and Assembly with the T cell Receptor. Cell, 127(2), 355-368
- Wei, R. R., Schnell, J. R., Sorger, P. K., Chou, J. J. and Harrison, S. C. (2006). Structure of a Central Component of the Yeast Kinetochore: the Spc24/Spc25p Globular Domain. Structure, 14(6), 1003-9
- Schnell, J. R., Zhou, G.-P., Zweckstetter, M., Rigby, A. C. and Chou, J. J. (2005). Rapid and Accurate Structure Determination of Coiled-Coil Domains using NMR Dipolar Couplings: Application to cGMP-Dependent Protein Kinase Ia. Protein Sci., 14(9), 2421-8
More Publications...
Research Images
Figure 1: The interaction of the antiviral drug rimantadine with the influenza A proton channel M2. The lipid-facing binding pocket is composed of the channel gating elements (Trp41 and Asp44) that are contributed from two adjacent TM helices (PDB accession code 2RLF; Schnell & Chou, 2008, Nature)
Figure 2: A schematic of the set-up (left), and an experimental trace (right) of a liposomal proton flux assay of the viral proton channel M2 (Pielak, Schnell & Chou, 2009, Proc. Natl. Acad. Sci. U.S.A.). M2 was inserted into lipid vesicles with equal concentrations of all ions both inside and out, but highly buffered inside, and only weakly buffered outside. Valinomycin is incorporated to allow free diffusion of potassium across the membrane. The assay is initiated by the addition of protons (as HCl) to the external solution, and proton conduction into the vesicles via M2 channels is monitored by recording changes in external pH. The experiment is terminated by addition of the proton uncoupler CCCP
Figure 3: The T-cell receptor complex (TCR) transmits antigen-binding information across the T lymphocyte membrane. Assembly of the TCR is dictated by sets of basic and acidic residues buried in the membrane bilayer (right; Call & Wucherpfennig, 2005, Annu. Rev. Immunol.) The structure of the zeta-zeta dimer provided the molecular details of how one such interaction occurs, and revealed additional polar contacts, including at least one bound water molecule, that stabilize the intermolecular assembly (left; Call & Schnell et al., 2006, Cell)
Contact: jason.schnell@bioch.ox.ac.uk
Graduate Student and Postdoctoral Positions: Enquiries with CV welcome