Séminaire

Séminaire
Conférencier invité
Vendredi 22 Mars 2013
Institut de Biologie Structurale J.P. Ebel
41, rue Jules Horowitz
F-38027 GRENOBLE Cedex 1
Tél. +33 (0)4 38 78 95 50 - Fax +33 (0)4 38 78 54 94
www.ibs.fr
A 11h - Salle des séminaires de l’IBS
Par Thomas Grutter
Equipe Chimie et Neurobiologie Moléculaire
UMR CNRS/Université de Strasbourg, Conception et Application de Molécules Bioactives
New Insights into ATP Binding and Channel
Gating in the P2X2 Receptor
P2X receptors are oligomeric ATP-gated ion channels selective to cations. Upon ATP
binding, structural rearrangements of the protein lead to the opening of the ion channel,
a process referred to as gating. In 2009, a first X-ray structure of a P2X receptor was
solved in a closed resting state confirming the trimeric stoichiometry of the ion channel.
However, the structure was solved without ATP and thus neither ATP binding sites nor the
conformational changes following agonist binding were visible. Based on this structure,
we have localized the ATP-binding sites in the P2X2 receptor extracellular domain through
an engineered affinity labeling-based approach with the affinity marker 8-thiocyano-ATP
(NCS-ATP). NCS-ATP is a P2X2 agonist that selectively cross-linked ATP sites at positions
Asn140 and Leu186. We showed that these residues are from two adjacent subunits and
are separated by about 18 Å in a P2X2 closed state homology model, thus defining a large
cavity shaped like an open jaw. Surprisingly, labeling of these positions resulted in two
distinct functional consequences, suggesting that ATP may bind to the receptor with at
least two opposite orientations; one leading to activation, the other to inhibition. More
recently, we have identified the structural changes of the ATP site accompanying receptor
activation by engineering extracellular zinc bridges at putative mobile regions. Based on
these data, we propose a model in which ATP binding near Leu186 favors jaw tightening
and drives channel opening, while binding of ATP near Asn140 prevents this tightening
and consequently, the channel fails to open. Remarkably, all these results, including the
jaw tightening mechanism, have been recently confirmed by a second X-ray structure,
in which the receptor was bound to ATP and resolved in an open channel conformation.
Certainly, this new information will accelerate our understanding of P2X receptor function
and pharmacology at the atomic level.
Hôte : J. Neyton (IBS/DIR)