Fre1p Cu2+ Reduction and Fet3p Cu1+ Oxidation Modulate Copper Toxicity in Saccharomyces cerevisiae

Department of Environmental Toxicology, University of California, Santa Cruz, California 95064, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2004; 278(50):50309-15. DOI: 10.1074/jbc.M307019200
Source: PubMed


Fre1p is a metalloreductase in the yeast plasma membrane that is essential to uptake of environmental Cu2+ and Fe3+. Fet3p is a multicopper oxidase in this membrane essential for high affinity iron uptake. In the uptake of Fe3+, Fre1p produces Fe2+ that is a substrate for Fet3p; the Fe3+ produced by Fet3p is a ligand for the iron permease, Ftr1p. Deletion of FET3 leads to iron deficiency; this deletion also causes a copper sensitivity not seen in wild type. Deletion of FTR1 leads to copper sensitivity also. Production in the ftr1Δ strain of an iron-uptake negative Ftr1p mutant, Ftr1p(RAGLA), suppressed this copper sensitivity. This Ftr1p mutant supported
the plasma membrane targeting of active Fet3p that is blocked in the parental ftr1Δ strain. A ferroxidase-negative Fet3p did not suppress the copper sensitivity in a fet3Δ strain, although it supported the plasma membrane localization of the Fet3p·Ftr1p complex. Thus, loss of membrane-associated
Fet3p oxidase activity correlated with copper sensitivity. Furthermore, in vitro Cu1+ was shown to be an excellent substrate for Fet3p. Last, the copper sensitivity of the fet3Δ strain was suppressed by co-deletion of FRE1, suggesting that the cytotoxic species was Cu1+. In contrast, deletion of CTR1 or of FET4 did not suppress the copper sensitivity in the fet3Δ strain; these genes encode the two major copper transporters in laboratory yeast strains. This result indicated that the
apparent cuprous ion toxicity was not due to excess intracellular copper. These biochemical and physiologic results indicate
that at least with respect to cuprous and ferrous ions, Fet3p can be considered a metallo-oxidase and appears to play an essential
role in both iron and copper homeostasis in yeast. Its functional homologs, e.g. ceruloplasmin and hephaestin, could play a similar role in mammals.

Full-text preview

Available from:
  • Source
    • "In our laboratory it has been previously demonstrated that cell-surface ferric and cupric reductase activity in C. albicans is regulated by both the iron and copper content of the medium (Morrissey et al., 1996). In the model organism Saccharomyces cerevisiae, the major ferric reductase protein, ScFre1, is also a cupric reductase (Shi et al., 2003). The reductive iron uptake system in S. cerevisiae shows homology to that of C. albicans , therefore it is possible that the same proteins are responsible for both ferric and cupric reductase activity in C. albicans. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The pathogenic yeast Candida albicans possesses a reductive iron uptake system which is active in iron-restricted conditions. The sequestration of iron by this mechanism initially requires the reduction of free iron to the soluble ferrous form, which is catalysed by ferric reductase proteins. Reduced iron is then taken up into the cell by a complex of a multicopper oxidase protein and an iron transport protein. Multicopper oxidase proteins require copper to function and so reductive iron and copper uptake are inextricably linked. It has previously been established that Fre10 is the major cell surface ferric reductase in C. albicans and that transcription of FRE10 is regulated in response to iron levels. We demonstrate here that Fre10 is also a cupric reductase and that Fre7 also makes a significant contribution to cell surface ferric and cupric reductase activity. It is also shown, for the first time, that transcription of FRE10 and FRE7 is lower in hyphae compared to yeast and that this leads to a corresponding decrease in cell surface ferric, but not cupric, reductase activity. This demonstrates that the regulation of two virulence determinants, the reductive iron uptake system and the morphological form of C. albicans, are linked.
    Preview · Article · Sep 2011 · Yeast
  • Source
    • "We also tested whether other metal ions—Cd(II), Cu(II), Mn(II), and Zn(II)—could competitively inhibit Fe uptake during shortterm experiments. Cu(I) is produced from Cu(II) by cell-surface reductases, and Cu(I) can be reoxidized by the ferroxidase enzyme in yeast (Shi et al. 2003, Stoj and Kosman 2003). Thus, we also examined the effects of Cu(I) on Fe uptake by using Cu(I)-specific ligands. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The centric diatom Thalassiosira pseudonana Hasle et Heimdal and the pennate diatom Phaeodactylum tricornutum Bohlin possess genes with translated sequences homologous to high-affinity ferric reductases present in model organisms. Thalassiosira pseudonana also possesses putative genes for membrane-bound ferroxidase (TpFET3) and two highly similar iron (Fe) permeases (TpFTR1 and TpFTR2), as well as a divalent metal (M2+) transporter belonging to the NRAMP superfamily (TpNRAMP). In baker’s yeast, the ferroxidase–permease complex transports Fe(II) produced by reductases. We investigated transcript abundances of these genes as a function of Fe quota (QFe). Ferric reductase transcripts are abundant in both species (15%–60% of actin) under low QFe and are down-regulated by 5- to 35-fold at high QFe, suggesting Fe(III) reduction is a common, inducible strategy for Fe acquisition in marine diatoms. Permease transcript abundance was regulated by Fe status in T. pseudonana, but we did not detect significant differences in expression of the copper (Cu)-containing ferroxidase. TpNRAMP showed the most dramatic regulation by QFe, suggesting a role in cellular Fe transport in either cell-surface uptake or vacuolar mobilization. We could not identify ferroxidase or permease homologues in the P. tricornutum genome. The up-regulation of genes in T. pseudonana that appear to be missing altogether from P. tricornutum as well as the finding that P. tricornutum seems to have an efficient system to acquire Fe′, suggest that diverse (and uncharacterized) Fe-uptake systems may be at play within diatom assemblages. Different uptake systems among diatoms may provide a mechanistic basis for niche differentiation with respect to Fe availability in the ocean.
    Full-text · Article · Jul 2007 · Journal of Phycology
  • Source
    • "In turn, these adaptive pathways depend on optimized expression by a network of regulators to produce successful pathogens , conveying pathogenic fitness within the unlucky human host[10]. Copper is essential to a number of cellular processes, such as respiration and iron uptake[11], and optimum copper homeostasis has been associated with the virulence of a number of intracellular pathogens including Listeria mono- cytogenes[12], Mycobacterium tuberculosis and Mycobacterium leprae[13]. The presence of specific host mechanisms to deprive the pathogenWaterman & Williamson Future Microbiol. "

    Preview · Article · Jul 2007 · Future Microbiology
Show more