Disease relevance of FET3

• Fre1p Cu2+ reduction and Fet3p Cu1+ oxidation modulate copper toxicity in Saccharomyces cerevisiae [1].

High impact information on FET3

• The FET3 gene of S. cerevisiae encodes a multicopper oxidase required for ferrous iron uptake [2].
• FET3 expression was required for FTR1 protein to be transported to the plasma membrane [3].
• In the budding yeast Saccharomyces cerevisiae, transcription of genes encoding for the high-affinity iron (FET3, FTR1) and copper (CTR1) transporters does not occur in the absence of heme [4].
• Thus, the environmental signal resulting from iron deprivation was transduced through the regulated binding of AFT1 to the FET3 promoter, followed by the activation of transcription [5].
• These effects may be explained by the failure of iron to repress transcription of FRE1, FRE2 and FET3 [6].

Biological context of FET3

• In this report, the 5'-flanking region of FET3, which encodes a copper-dependent oxidase required for iron transport, was analyzed and found to contain a DNA sequence responsible for AFT1-regulated gene expression [5].
• 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 [1].
• Yeast strains defective in endocytosis (Deltaend4) show a reduced iron-induced loss of Fet3p-Ftr1p [7].
• Suppression of the fet3 fet4 mutant phenotype by FET5 overexpression required the putative FTR1 transporter subunit of the high-affinity system [8].
• Cells that contain a functional FET3 gene product exhibited an iron-dependent non-mitochondrial increase in oxygen consumption [9].

Anatomical context of FET3

• Ferrous ions are then transported across the plasma membrane through the FET3 oxidase-FTR1 permease complex [10].
• Atx1p localizes to the cytosol, and our studies indicate that it functions as a carrier for copper that delivers the metal from the cell surface Ctr1p to Ccc2p and then to Fet3p within the secretory pathway [11].
• In cells with a deletion in the vacuolar protease PEP4, high iron medium leads to the accumulation of Fet3p and Ftr1p in the vacuole [7].
• To further characterize the protein, we have isolated Fet3p from yeast membranes and purified the protein to apparent homogeneity [12].
• First, like ccc2 mutants, sec mutants blocked in the secretory pathway at steps prior to and including the Golgi complex failed to deliver radioactive copper to Fet3p [13].

Associations of FET3 with chemical compounds

• Deletion of ARN3 did not prevent yeast from using ferrioxamine B as an iron source; however, deletion of ARN3 and FET3, a component of the high affinity ferrous iron transport system, did prevent uptake of ferrioxamine-bound iron and growth on ferrioxamine as an iron source [14].
• High affinity copper uptake mediated by the copper transport protein encoded by CTR1 is required to provide the FET3 protein with copper, and thus copper uptake is indirectly required for ferrous iron uptake [15].
• The active domain of Aft1 necessary for activation of the FET3 promoter by cisplatin is identical to the one required for activation by bathophenanthroline sulfonate, an inhibitor of cellular iron uptake [16].
• Specific aspartate residues in FET3 control high-affinity iron transport in Saccharomyces cerevisiae [17].
• Another three ORFs (4121orfR003, 4121orfR004 and 4121orfRN001) were highly homologous to FET3 multi-copper oxidase, glucose transport protein, and hypothetical protein of YIL106w on chromosome IX, respectively [18].

Physical interactions of FET3

• Despite the inability to induce transcription under low iron conditions, chromatin immunoprecipitation demonstrated that Aft1p binds to the FET3 promoter in the absence of heme [19].
• 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 [20].

Regulatory relationships of FET3

• Aft1 protein is required for maintaining detectable non-induced level of FET3 expression and for induction of FRE2 in iron starvation conditions [10].
• By indirect immunofluorescence, Fre3p was expressed on the plasma membrane in a pattern similar to that of Fet3p, a component of the high affinity ferrous transporter [21].

Other interactions of FET3

• This Ftr1p mutant supported the plasma membrane targeting of active Fet3p that is blocked in the parental ftr1delta strain [1].
• We now provide evidence that Atx1p helps deliver copper to the copper requiring oxidase Fet3p involved in iron uptake. atx1Delta null mutants are iron-deficient and are defective in the high affinity uptake of iron [11].
• The yeast FET5 gene encodes a FET3-related multicopper oxidase implicated in iron transport [8].
• Instead, CCC2 mutant cells lacked a copper-dependent oxidase activity associated with the extracytosolic domain of the FET3-encoded protein, a ceruloplasmin homologue previously shown to be necessary for high-affinity iron uptake in yeast [22].
• This was shown by the Fet4p-dependence of copper activation of Fet3p, the copper oxidase that supports high affinity iron uptake in yeast [23].

Analytical, diagnostic and therapeutic context of FET3

• The modification of cellular iron metabolism, which involved the increased expression of high-affinity iron transport genes (FET3 and FTR1), was detected via Northern blot analysis [24].
• Site-directed mutagenesis of the yeast multicopper oxidase Fet3p [25].
• The electronic and geometric structure of the Fe(II) substrate bound to Fet3p and hCp has been studied for the first time, using variable-temperature variable field magnetic circular dichroism (VTVH MCD) spectroscopy [26].

References