Iron‐regulatory protein‐1 (IRP‐1) is highly conserved in two invertebrate species

Abstract

Iron-regulatory protein-1 (IRP-1) plays a dual role as a regulatory RNA-binding protein and as a cytoplasmic aconitase. When bound to iron-responsive elements (IRE), IRP-1 post-transcriptionally regulates the expression of mRNAs involved in iron metabolism. IRP have been cloned from several vertebrate species. Using a degenerate-primer PCR strategy and the screening of data bases, we now identify the homologues of IRP-1 in two invertebrate species, Drosophila melanogaster and Caenorhabditis elegans. Comparative sequence analysis shows that these invertebrate IRP are closely related to vertebrate IRP, and that the amino acid residues that have been implicated in aconitase function are particularly highly conserved, suggesting that invertebrate IRP may function as cytoplasmic aconitases. Antibodies raised against recombinant human IRP-1 immunoprecipitate the Drosophila homologue expressed from the cloned cDNA. In contrast to vertebrates, two IRP-1 homologues (Drosophila IRP-1A and Drosophila IRP-1B), displaying 86% identity to each other, are expressed in D. melanogaster. Both of these homologues are distinct from vertebrate IRP-2. In contrast to the mammalian system where the two IRP (IRP-1 and IRP-2) are differentially expressed, Drosophila IRP-1A and Drosophila IRP-1B are not preferentially expressed in specific organs. The localization of Drosophila IRP-1A to position 94C1-8 and of Drosophila IRP-1B to position 86B3-6 on the right arm of chromosome 3 and the availability of an IRP-1 cDNA from C. elegans will facilitate a genetic analysis of the IRE/IRP system, thus opening a new avenue to explore this regulatory network.Keywords : Drosophila melanogaster; Caenorhabditis elegans ; iron-regulatory protein; RNA binding; iron regulation.The post-transcriptional regulation of mRNAs involved in tion of IRP-1 and IRP-2 occurs post-translationally by distinct mechanisms. Striking similarities were discovered between cellular iron metabolism by iron-regulatory proteins (IRP) and iron-responsive elements (IRE) is widely used in the animal IRP-1 and mitochondrial [4, 5] and bacterial aconitases [6, 7], which are Fe-S proteins that reversibly convert citrate to isokingdom. In mammals, where this system is best characterized, IRP control the translation of mRNAs for the iron-storage pro-citrate. This finding led to experiments showing that IRP-1 is converted in iron-replete cultured cells into a cytoplasmic aconitein ferritin, the erythroid 5-aminolevulinate synthase a rate-limiting enzyme for the main iron-utilization pathway, and the mito-tase by insertion of a [4Fe-4S] cluster liganded to three highly conserved cysteine residues [8Ϫ10]. The [4Fe-4S] IRP-1 is inchondrial aconitase, by binding to a single IRE located in the 5′ active in IRE binding. Removal or loss of the Fe-S cluster conuntranslated region (UTR) of the respective messages. IRP verts the aconitase form into an RNA-binding protein. In conbound to multiple IRE in the 3′ UTR of the transferrin receptor trast to IRP-1, IRP-2 does not exhibit aconitase activi...

A Developmentally Regulated Aconitase Related to Iron-regulatory Protein-1 Is Localized in the Cytoplasm and in the Mitochondrion of Trypanosoma brucei

“…Since members of both aconitase subfamilies were identified in invertebrates, e.g. Caenorhabditis elegans and Drosophila melanogaster (73), specialization of mitochondrial and cytoplasmic aconitase functions seems to have occurred early during animal evolution. Here we report on a protozoan aconitase which belongs to the IRP-1 subfamily but localizes in the mitochondrion as well as in the cytoplasm.…”

Cytosolic Aconitase and Ferritin Are Regulated by Iron inCaenorhabditis elegans

“…elegans-The C. elegans genome possesses two aconitase genes, which are designated gei-22/aco-1 and aco-2. gei-22/ aco-1 encodes a protein that shares ϳ63% identity with mammalian IRP-1 (16), D. melanogaster IRP-1A and 1B (16), and A. thaliana (13) and T. brucei (17) IRP-1s while sharing only ϳ24% identity to porcine (28) and C. elegans mitochondrial aconitases ( Fig. 1).…”

“…IRP-1s have been identified in a wide variety of organisms, including bacteria (10 -12), plants (13)(14)(15), and animals (16,17). IRP-1s share a high degree of amino acid identity among different species.…”

“…IRP-1s share a high degree of amino acid identity among different species. For example, mammalian IRP-1s are Ͼ90% identical and are highly homologous to IRP-1s from other organisms, including Caenorhabditis elegans (64% identity) (16), Arabidopsis thaliana (59% identity) plants (13), Trypanosome brucei (64% identity) (17), and Escherichia coli (52% identity) (10). In contrast, IRP-1s share only ϳ20% amino acid identity to mitochondrial aconitases.…”

Homeostatic Mechanisms for Iron Storage Revealed by Genetic Manipulations and Live Imaging of Drosophila Ferritin

“…In contrast, no IRE is present in Fer2LCH mRNA . IRP homologs are expressed in the fly (Muckenthaler et al 1998), and one homolog (IRP-1A) has been shown to bind to IREs from both Drosophila and mammals (Lind et al 2006).…”