Structural changes associated with switching activities of human iron regulatory protein 1.
Metazoan iron regulatory protein 1 is a dual activity protein, being either an aconitase or a regulatory factor binding to messenger RNA involved in iron homeostasis. Sequence comparisons and site-directed mutagenesis experiments have supported a structural relationship between mitochondrial aconitase and iron regulatory protein 1. The structural properties of human recombinant iron regulatory protein 1 have been probed in the present work. Although iron-free iron regulatory protein 1 displays a significantly larger radius of gyration measured by small-angle neutron scattering than calculated for mitochondrial aconitase, binding of either the [4Fe-4S] cluster needed for aconitase activity or of a RNA substrate turns iron regulatory protein 1 into a more compact molecule. These conformational changes are associated with the gain of secondary structural elements as indicated by circular dichroism studies. They likely involve alpha-helices covering the substrate binding cleft of cytosolic aconitase, and they suggest an induced fit mechanism of iron-responsive element recognition. These studies refine previously proposed models of the "iron-sulfur switch" driving the biological function of human iron regulatory protein 1, and they provide a structural framework to probe the relevance of the numerous cellular molecules proposed to affect its function.
Brazzolotto
Xavier
X
Commissariat à l'Energie Atomique-Grenoble, Département de Biologie Moléculaire et Structurale, 38054 Grenoble Cedex 9, France.
Timmins
Peter
P
Dupont
Yves
Y
Moulis
Jean-Marc
JM
D000154:Aconitate Hydratase / Q000378:metabolism; D000818:Animals; D002942:Circular Dichroism; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D009502:Neutrons; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012542:Scattering, Radiation; D013552:Swine
D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D000154:Aconitate Hydratase