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J. Biol. Chem., Vol. 281, Issue 40, 29929-29937, October 6, 2006

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Odorant Binding and Conformational Dynamics in the Odorant-binding Protein^*

Eric Hajjar¹, David Perahia, Hélène Débat, Claude Nespoulous, and Charles H. Robert²

From the CNRS UMR8619, Modélisation et Ingénierie des Protéines, Université Paris-Sud, 91405 Orsay, France and the French National Institute for Agricultural Research, NOPA-BOG, 78352 Jouy-en-Josas, France

In mammals, the olfactory epithelium secretes odorant-binding proteins (OBPs), which are lipocalins found freely dissolved in the mucus layer protecting the olfactory neurons. OBPs may act as passive transporters of predominantly hydrophobic odorant molecules across the aqueous mucus layer, or they may play a more active role in which the olfactory neuronal receptor recognizes the OBP-ligand complex. To better understand the molecular events accompanying the initial steps in the olfaction process, we have performed molecular dynamics studies of rat and pig OBPs with the odorant molecule thymol. These calculations provide an atomic level description of conformational changes and pathway intermediates that remain difficult to study directly. A series of eight independent molecular dynamics trajectories of rat OBP permitted the observation of a consensus pathway for ligand unbinding and the calculation of the potential of mean force (PMF) along this path. Titration microcalorimetry confirmed the specific binding of thymol to this protein with a strong hydrophobic component. In both rat and pig OBPs we observed lipocalin strand pair opening in the presence of ligand, consistent with potential roles of these proteins in olfactive receptor recognition.

Received for publication, May 19, 2006 , and in revised form, July 11, 2006.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1-S4.

¹ Current address: Computational Biology Unit BCCS, University of Bergen, Bergen, Norway.

² To whom correspondence should be addressed: MIP, CNRS UMR8619, Bât. 430, Université Paris-sud, 91405 Orsay, France.

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