Implication des protéines IRP (Iron Regulatory Protein) dans le métabolisme du fer chez les animaux

Abstract : Iron Regulatory Protein 1 (IRP1) is a cytosolic protein that regulates the intracellular iron concentration in metazoans by a post-transcriptional mechanism. It binds specific sequences, called Iron responsive Element (IRE), on the untranslated regions of different mRNA involved in iron homeostasis. When iron is abundant, IRP1 looses its RNA-binding activity, assembles a [4Fe-4S] cluster and becomes an aconitase. The building and destruction of the iron-sulfur cluster is a key feature of the regulation.
The recombinant human IRP1 has been purified as the aconitase [4Fe-4S] form and the reaction of various compounds able to modify the IRP1 activity has been studied. Several reactive oxygen species in small excess over the protein produce the inactive [3Fe-4S] form. The cytostatic drug, doxorubicin, changes IRP1 activity, but its impact depends on the conditions and involves several mechanisms. Large amounts of 2-mercaptoethanol fully convert IRP1 into its IRE-binding form. Ethanol plays a similar role, and these chemicals act as solvents in this process.
IRP1 has been investigated by a two hybrid approach in the yeast Saccharomyces cerevisiae. No genuine physiological partners have been discovered. Alternatives approaches may be needed toward this aim.
The possibility of measuring IRE binding to IRP1 by a fluorescent assay coupled to capillary electrophoresis has been probed. Our data do not validate the method but they provide indications about how to improve the sensitivity and efficiency to develop it.
Conformational changes between the two active forms of IRP1 have been analyzed by two complementary methods. The building of some secondary structure elements depends on the form of the protein being studied and on the binding of substrates. The hydrodynamic properties also vary between these different states. Without additional structural information on IRP1, these studies give an idea about how IRP1 fulfils its regulatory function.
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Xavier Brazzolotto. Implication des protéines IRP (Iron Regulatory Protein) dans le métabolisme du fer chez les animaux. Sciences du Vivant [q-bio]. Université Joseph-Fourier - Grenoble I, 2001. Français. ⟨tel-00193675⟩

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