The cell membrane constitutes the main barrier for ion movement, and specialized proteins have been selected to catalyze the transport of various ions across the membrane: ion channels. Ion channels are integral membrane proteins (they cross the entire length of the membrane), and carry a hydrophilic water-filled pore that permit the passive flow of ions down their electrochemical gradient.

Our group is interested in a particular class of channels, which carry an internal gate undergoing opening/closing motions in response to ligands: Ligand-gated ion channel (LGICs). Among them, the pentameric LGICs (pLGICs) compose a large superfamily of phylogeneticaly-related membrane proteins, for which more than 40 genes are found in the human, accomplish a wide range of function in the cellular communication, particularly in neuronal communication. This superfamily includes nicotinic acetylcholine receptors (nAChRs), which mediate important pathways of cholinergic neuromodulation in the brain, GABAAreceptors, which mediate the majority of the inhibitory transmission in the brain, as well as glycine and 5HT3receptors. These proteins are involved in numerous human pathologies, and are the target of important therapeutic drugs including nicotinic derivatives, anxiolytics, alcohols and general anesthetics.

We aim at understanding, at an atomic resolution, the molecular mechanism governing the function of these proteins. They are known to fold as symmetrical pentamers in the membrane, and to undergo global allosteric transitions in the course of activation and desensitization.

In the search of pLGIC prototypes suitable for X-ray crystallographic approaches, our group was the first one to identify a functional bacterial homolog from the archaic cyanobacterium Gloeobacter violaceus. We overexpressed and purified this proton-gated ion channel, and its crystallization low pH by the Unit of Structural dynamics of macromolecules headed by Marc Delarue (Pasteur Institute), yielded the 2.9 Å structure of an open conformation of the channel, that gives an atomic resolution picture of both the mechanisms of ion translocation within the channel and of the activation process. We are currently combining X-ray crystallography, biophysical and electrophysiological approaches to understand the allosteric transitions of these prototypic bacterial channels, and their regulation by pharmacological ligands. Our latest study identified the binding site of two clinically used general anesthetics desflurane and propofol. This provides insights into the mechanism of action of these hydrophobic molecules, and open the way for the design of novel classes of allosteric effectors acting at the level of the transmembrane domain.

Keywords: membrane protein, ion channel, allostery, electrophysiology, nicotinic receptor, GABAA receptor

Corringer, P.J., Baaden, M., Bocquet, N., Delarue, M., Dufresne, V., Nury, H., Prevost, M., Van Renterghem, C.^, Atomic structure and dynamics of pentameric ligand-gated ion channels: new insight from bacterial homologues, J. Physiol, 588(Pt 4):565-72 (2010)

Nury H, Bocquet N, Le Poupon C, Raynal B, Haouz A, Corringer PJ, Delarue M. Crystal Structure of the Extracellular Domain of a Bacterial Ligand-Gated Ion Channel. J Mol Biol.395, 1114–1127(2010)

Weng Y, Yang L, Corringer PJ, Sonner JM. Anesthetic Sensitivity of the Gloeobacter violaceus Proton-Gated Ion Channel. Anesth Analg. 110 (1):59-63 (2010)

Bocquet, N., Nury, H., Baaden, M., Le Poupon, C., Changeux, J.P., Delarue, M., Corringer, P.J. X-ray structure of a pentameric ligand-gated ion channel in an apparently open conformation, Nature, 457(7225) :111-4 (2009)

Bocquet, N., Prado de Carvalho, L., Cartaud, J., Neyton, J., Le Poupon, C., Taly, A., Grutter, T., Changeux, J.P., Corringer, P.J. A prokaryotic proton-gated ion channel from the nicotinic acetylcholine receptor family, Nature, 445: 116-119 (2007)