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Etude structurale du mécanisme d'échange de chaînes des dimères de la protéine HU d'E. coli

Abstract : HU is a histone like protein of bacteria involved in numerous biological functions such as DNA compaction, transcription, replication and repair. In E. coli, three HU dimers types are present (HUα2, HUβ2 et HUαβ) and show distinct biological roles. The heterodimer is formed from homodimers through a peptidic chain exchange. A model of this mechanism has been proposed by Ramstein and coworkers (J.M.B. 331, 101-121 2003) and was used as a starting point for this study. In this model, homodimers undergo a conformationnal change from a native state (N2) toward an intermediate state (I2). Then, I2 homodimers associate to form a transient heterotetramer which then dissociate into heterodimers. The main aim of this work was to characterize the structure and kinetic of each step of this mechanism. Major results of this work include the elucidation of two original crystal structures : HUβ2 from E. coli and HU from L. lactis in N2 states. A model of the partially disordered I2 state has also been proposed for HUβ2 and HUα2, and is consistent with results obtained from both NMR and molecular dynamics experiments. In addition, the existence of a low concentration tetrameric conformation has been evidenced by native mass spectrometry experiments. A protocol of production/purification/oxydation as been developped for the introduction of disulfide bridges in order to stabilize this conformation and characterize its structure. Together, results obtained from these different biophysical means refine our understanding of the chain exchange mechanism at the molecular level and highlight the role of the I2 conformation in controlling HU dimers composition.
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Submitted on : Monday, January 2, 2017 - 1:48:55 AM
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  • HAL Id : tel-01424222, version 1



Rémy Le Meur. Etude structurale du mécanisme d'échange de chaînes des dimères de la protéine HU d'E. coli. Sciences agricoles. Université d'Orléans, 2015. Français. ⟨NNT : 2015ORLE2004⟩. ⟨tel-01424222⟩



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