title: A chemical chaperone induces inhomogeneous conformational changes in flexible proteins.
abstract: Organic osmolytes also known as chemical chaperones are major cellular compounds that favor, by an unclear mechanism, protein's compaction and stabilization of the native state. Here, we have examined the chaperone effect of the naturally occurring trimethylamine N-oxide (TMAO) osmolyte on a loosely packed protein (LPP), known to be a highly flexible form, using an apoprotein mutant of the flavin-dependent RNA methyltransferase as a model. Thermal and chemical denaturation experiments showed that TMAO stabilizes the structural integrity of the apoprotein dramatically. The denaturation reaction is irreversible indicating that the stability of the apoprotein is under kinetic control. This result implies that the stabilization is due to a TMAO-induced reconfiguration of the flexible LPP state, which leads to conformational limitations of the apoprotein likely driven by favorable entropic contribution. Evidence for the conformational perturbation of the apoprotein had been obtained through several biophysical approaches notably analytical ultracentrifugation, circular dichroism, fluorescence spectroscopy, labelling experiments and proteolysis coupled to mass spectrometry. Unexpectedly, TMAO promotes an overall elongation or asymmetrical changes of the hydrodynamic shape of the apoprotein without alteration of the secondary structure. The modulation of the hydrodynamic properties of the protein is associated with diverse inhomogenous conformational changes: loss of the solvent accessible cavities resulting in a dried protein matrix; some side-chain residues initially buried become solvent exposed while some others become hidden. Consequently, the TMAO-induced protein state exhibits impaired capability in the flavin binding process. Our study suggests that the nature of protein conformational changes induced by the chemical chaperones may be specific to protein packing and plasticity. This could be an efficient mechanism by which the cell controls and finely tunes the conformation of the marginally stable LPPs to avoid their inappropriate protein/protein interactions and aggregation.
authors.affiliation: Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France. djemel.hamdane@college-de-france.fr.
authors.forename: Djemel
authors.initials: D
authors.lastname: Hamdane
authors.affiliation: Macromolecular Interaction Platform of I2BC, UMR 9198, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 1 avenue de la terrasse, 91191 Gif Sur Yvette, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Velours
authors.affiliation: CNRS, Centre de Recherche de Gif, SICaPS, F-91198 Gif-sur-Yvette Cedex, France.
authors.forename: David
authors.initials: D
authors.lastname: Cornu
authors.affiliation: Macromolecular Interaction Platform of I2BC, UMR 9198, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 1 avenue de la terrasse, 91191 Gif Sur Yvette, France.
authors.forename: Magali
authors.initials: M
authors.lastname: Nicaise
authors.affiliation: Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France. djemel.hamdane@college-de-france.fr.
authors.forename: Murielle
authors.initials: M
authors.lastname: Lombard
authors.affiliation: Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France. djemel.hamdane@college-de-france.fr.
authors.forename: Marc
authors.initials: M
authors.lastname: Fontecave
mesh_terms: D000818:Animals; D001059:Apoproteins; D002942:Circular Dichroism; D006801:Humans; D018832:Molecular Chaperones; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
chemical_list: D001059:Apoproteins; D018832:Molecular Chaperones