Adsorption des protéines sur les nanomatériaux. Biochimie et physico-chimie d’un nouveau stress

Abstract : Nanomaterials raise new questions in environmental and human toxicology and represent a novel interface with specific properties with the biological medium. Several unknown remain to explain all the mechanisms of toxicity, especially at the molecular lever. When they enter the biological medium, nanoparticles get covered by a protein corona. This corona yields to a new “biological identity” that controls the cellular response to nanoparticles and their fate in the organism. We studied the adsorption of model proteins on nanostructured silica. The first part is dedicated to the characterization of nanoporous silica and silica nanoparticles that we used. Then the adsorption of myoglobin, hemoglobin and protein mixture from yeast cells was studied to determine the thermodynamic and physical-chemical parameters of protein adsorption on silica. The enrichment of basic residues, gathered in charge clusters, favors the adsorption of proteins by the formation of electrostatic interactions with the charged surface of silica, independently of the global charge of the protein. On the contrary, the enrichment in aromatic residues is unfavorable to protein adsorption because they form π-π interactions that rigidify the protein structure. The identification of adsorbed and non-adsorbed proteins from a complex medium could also be used for cellular toxicity studies. From the study of the structure, the dynamics and the activity of myoglobin and hemoglobin adsorbed on silica nanoparticles, we tried to define the state of an adsorbed protein. The structural study, based on circular dichroism, fluorescence, infrared, X-ray and UV-visible spectroscopy and microcalorimetry, shows a substantial partial structure loss of adsorbed proteins together with a high conformational heterogeneity, without major modifications of the heme structure. Two potential interaction sites of myoglobin with silica nanoparticles have been identified by a footprinting technique. The study of adsorbed myoglobin dynamics by elastic and inelastic neutron scattering highlighted the important decrease of protein dynamics that occurs upon adsorption. However, despite the structure loss, adsorbed metmyoglobin retains almost all of its activity of ligand binding. Unexpectedly, adsorbed hemoglobin shows an increase of its oxygen affinity and a decrease of its cooperativity, without any dissociation of the tetramer. This effect can be reproduced on human hemoglobin, cross-linked DCL hemoglobin and variant S hemoglobin. Besides, two effectors allow modulating the affinity of adsorbed hemoglobin. Despite the extent of structural and activity changes, all these modifications are entirely reversible upon desorption in soft conditions. The adsorption of hemoproteins on silica nanoparticles depicts a new sort of stress with resilience for proteins in terms of structure, dynamics and activity relationship.
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Stéphanie Devineau. Adsorption des protéines sur les nanomatériaux. Biochimie et physico-chimie d’un nouveau stress. Autre. Université Paris Sud - Paris XI, 2013. Français. ⟨NNT : 2013PA112215⟩. ⟨tel-00903842v2⟩

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