Siderophore-Iron Uptake in Saccharomyces cerevisiae

Siderophores are small organic compounds with high affinity for ferric iron. Microorganisms commonly acquire iron via siderophore secretion and uptake. Here we report the characterization of the siderophore transporter CaArn1p in the fungal pathogen Candida albicans. Deletion of CaARN1 reduced the ability of C. albicans to use iron bound to the hydroxamate-type siderophore ferrichrome and abolished it when two high-affinity iron permease genes (CaFTR1 and CaFTR2) were also deleted, indicating a role of CaArn1p as well as the permeases in ferrichrome-iron uptake. Caarn1⌬ (but not Caftr1⌬Caftr2⌬) assimilated iron from another hydroxamate-type siderophore, ferrioxamine B, suggesting that iron uptake from this compound depends on the permeases, but not on CaArn1p. Northern blot analysis revealed that the transcription repressor CaTup1p repressed CaARN1 expression under iron-replete conditions via the DNA-binding protein Rfg1p. Green fluorescent protein-tagged CaArn1p was observed predominantly in the plasma membrane, with some in the cytoplasm as distinct spots. The number of these spots increased with the increase in ferrichrome concentration, suggesting that CaArn1p internalization might be a mechanism for ferrichrome-iron uptake or for recycling the transporter. Caarn1⌬ did not show reduced virulence when injected into the blood stream of mice, implying that CaArn1p is not required for iron uptake along this route of infection.

Section: Discussionsupporting

confidence: 88%

“…PCR-amplified CaARN1 and CaACT1 DNA fragments were used as probes. 47). A few bright spots were also seen in the cytoplasm of some cells.…”

Section: Iron-responsive Regulation Of Caarn1mentioning

confidence: 99%

Characterization and Functional Analysis of the Siderophore-Iron Transporter CaArn1p in Candida albicans

Bai

Zheng

et al. 2002

“…In addition to ferrous iron which is used by the high affinity iron uptake system (Fet3p/Ftr1p), S. cerevisiae can utilize siderophores synthesized by fungi and bacteria. Siderophores are imported by four siderophore transporters (Arn1-4p) with distinct substrate specificities (25)(26)(27), or their ferric iron can be released, reduced, and transported by the high affinity iron uptake system (25). A triple deletion strain ⌬YOR382⌬YOR383⌬YDR534 had no obvious growth defect (data not shown).…”

Section: The New Members Of the Iron Regulon Play A Role In Ironmentioning

confidence: 99%

“…indicates that a direct role for frataxin in heme and iron cluster pathways is still questionable. To simplify the scheme, ferric reductases have not been shown and siderophore transporters have been localized to the plasma membrane even though there is good evidence that Arn1p and ARN3p localize to intracellular vesicles (25,26).…”

Section: Figmentioning

confidence: 99%

Mitochondrial Control of Iron Homeostasis

Foury¹,

Talibi

2001

181

Deletion of YFH1, the yeast frataxin homologue gene, elicits mitochondrial iron accumulation and alters cellular iron homeostasis. Here, we report a genome wide analysis of gene expression in a yfh1(⌬YFH1) deleted strain. Frataxin deficiency results in enhanced expression of some 70 genes including a set of genes, called the iron regulon, that are under the control of the ironsensing transcription factor AFT1. Five new AFT1-dependent genes, YOR382w, YOR383c, YDR534c, YLR136c, and YLR205c were found. The first three genes presumably encode cell-wall glycosylphosphatidylinositol anchor proteins and exhibit a 30 -100-fold increased expression. The triple deletion of these genes decreases efficiency in utilization of the iron of ferrioxamine B by the yeast cell. YLR136c bears homology to tristetraproline proteins, which are post-transcriptional regulators in mammalian cells. Deletion of YLR136c increases the mRNA levels of iron regulon members. YLR205c bears homology to heme oxygenases. Our data show that frataxin deficiency elicits iron mobilization from all iron sources in an AFT1-dependent manner. Wild-type and ⌬YFH1 glycerol-grown cells exhibit similar high respiration rates, no mitochondrial iron accumulation, and high expression of the iron regulon, suggesting that under these conditions little iron is extruded from mitochondria. These data suggest that the activity of Yfh1p is not essential in cells grown on glycerol. This study has also revealed unexpected links between mitochondria and remote metabolic pathways since frataxin deficiency also enhances the expression of genes such as HSP30, that escape to AFT1 control. Finally, no oxidative stress gene is induced.

“…Siderophore-iron uptake can be accomplished by either extracellular reduction and subsequent uptake of the iron by the high affinity iron transport system Fet3p/Ftr1p or by the uptake of siderophore-iron complexes by specific transporters belonging to the major facilitator super family (4,5). The hydroxamatetype siderophores ferrioxamine B, triacetyl fusarinine C, and ferrichrome are taken up by the S. cerevisiae siderophore-iron transporters Arn1p, Arn2p, and Arn3p (5)(6)(7)(8). Arn4p was found to be specific for the catecholate-type bacterial siderophore enterobactin (9).…”

mentioning

confidence: 99%

Identification of a Candida albicans Ferrichrome Transporter and Its Characterization by Expression inSaccharomyces cerevisiae

Ardon

Bussey²,

Philpott³

et al. 2001

Saccharomyces cerevisiae can accumulate iron through the uptake of siderophore-iron. Siderophore-iron uptake can occur through the reduction of the complex and the subsequent uptake of iron by the high affinity iron transporter Fet3p/Ftr1p. Alternatively, specific siderophore transporters can take up the siderophore-iron complex. The pathogenic fungus Candida albicans can also take up siderophore-iron. Here we identify a C. albicans siderophore transporter, CaArn1p, and characterize its activity. CaARN1 is transcriptionally regulated in response to iron. Through expression studies in S. cerevisiae strains lacking endogenous siderophore transporters, we demonstrate that CaArn1p specifically mediates the uptake of ferrichrome-iron. Iron-ferrichrome and galliumferrichrome, but not desferri-ferrichrome, could competitively inhibit the uptake of iron from ferrichrome. Uptake of siderophore-iron resulting from expression of CaARN1 under the control of the MET25-promoter in S. cerevisiae was independent of the iron status of the cells and of Aft1p, the iron-sensing transcription factor. These studies demonstrate that the expression of CaArn1p is both necessary and sufficient for the nonreductive uptake of ferrichrome-iron and suggests that the transporter may be the only required component of the siderophore uptake system that is regulated by iron and Aft1p.