title: Folding and turnover of human iron regulatory protein 1 depend on its subcellular localization.
abstract: Aconitases are iron-sulfur hydrolyases catalysing the interconversion of citrate and isocitrate in a wide variety of organisms. Eukaryotic aconitases have been assigned additional roles, as in the case of the metazoan dual activity cytosolic aconitase-iron regulatory protein 1 (IRP1). This human protein was produced in yeast mitochondria to probe IRP1 folding in this organelle where iron-sulfur synthesis originates. The behaviour of human IRP1 was compared with that of genuine mitochondrial (yeast or human) aconitases. All enzymes were functional in yeast mitochondria, but IRP1 was found to form dense particles as detected by electron microscopy. MS analysis of purified inclusion bodies evidenced the presence of human IRP1 and alpha-ketoglutarate dehydrogenase complex component 1 (KGD1), one of the subunits of alpha-ketoglutarate dehydrogenase. KGD1 triggered formation of the mitochondrial aggregates, because the latter were absent in a KGD1(-) mutant, but it did not efficiently do so in the cytosol. Despite the iron-binding capacity of IRP1 and the readily synthesis of iron-sulfur clusters in mitochondria, the dense particles were not iron-rich, as indicated by elemental analysis of purified mitochondria. The data show that proper folding of dual activity IRP1-cytosolic aconitase is deficient in mitochondria, in contrast to genuine mitochondrial aconitases. Furthermore, efficient clearance of the aggregated IRP1-KGD1 complex does not occur in the organelle, which emphasizes the role of molecular interactions in determining the fate of IRP1. Thus, proper folding of human IRP1 strongly depends on its cellular environment, in contrast to other members of the aconitase family.
authors.affiliation: Laboratoire de Biophysique Moléculaire et Cellulaire, UMR-CNRS 5090/Université Joseph Fourier, CEA-Grenoble, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Martelli
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Salin
authors.forename: Camille
authors.initials: C
authors.lastname: Dycke
authors.forename: Mathilde
authors.initials: M
authors.lastname: Louwagie
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Andrieu
authors.forename: Pierre
authors.initials: P
authors.lastname: Richaud
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Moulis
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D002479:Inclusion Bodies / Q000378:metabolism / Q000648:ultrastructure; D035941:Iron Regulatory Protein 1 / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D007655:Ketoglutarate Dehydrogenase Complex / Q000235:genetics / Q000378:metabolism; D013058:Mass Spectrometry; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000378:metabolism
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D007655:Ketoglutarate Dehydrogenase Complex; D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1