Human cytoplasmic aconitase (Iron regulatory protein 1) is converted into its [3Fe-4S] form by hydrogen peroxide in vitro but is not activated for iron-responsive element binding.
Iron regulatory protein 1 (IRP1) regulates the synthesis of proteins involved in iron homeostasis by binding to iron-responsive elements (IREs) of messenger RNA. IRP1 is a cytoplasmic aconitase when it contains a [4Fe-4S] cluster and an RNA-binding protein after complete removal of the metal center by an unknown mechanism. Human IRP1, obtained as the pure recombinant [4Fe-4S] form, is an enzyme as efficient toward cis-aconitate as the homologous mitochondrial aconitase. The aconitase activity of IRP1 is rapidly lost by reaction with hydrogen peroxide as the [4Fe-4S] cluster is quantitatively converted into the [3Fe-4S] form with release of a single ferrous ion per molecule. The IRE binding capacity of IRP1 is not elicited with H(2)O(2). Ferrous sulfate (but not other more tightly coordinated ferrous ions, such as the complex with ethylenediamine tetraacetic acid) counteracts the inhibitory action of hydrogen peroxide on cytoplasmic aconitase, probably by replenishing iron at the active site. These results cast doubt on the ability of reactive oxygen species to directly increase IRP1 binding to IRE and support a signaling role for hydrogen peroxide in the posttranscriptional control of proteins involved in iron homeostasis in vivo.
Département de Biologie Moléculaire et Structurale, Laboratoire Métalloprotéines, Commissariat à l'Energie Atomique, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
X
X
Brazzolotto
J
J
Gaillard
K
K
Pantopoulos
M W
MW
Hentze
J M
JM
Moulis
D000154:Aconitate Hydratase / Q000737:chemistry / Q000378:metabolism*; D003497:Cyclic N-Oxides; D003593:Cytoplasm / Q000201:enzymology; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D035941:Iron Regulatory Protein 1; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D013113:Spin Labels; D013379:Substrate Specificity; D013481:Superoxides / Q000378:metabolism / Q000494:pharmacology
D003497:Cyclic N-Oxides; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D013113:Spin Labels; D013481:Superoxides; C098505:5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide; D006861:Hydrogen Peroxide; D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1