The Fe(II) permease Fet4p functions as a low affinity copper transporter and supports normal copper trafficking in Saccharomyces cerevisiae.
The plasma-membrane of Saccharomyces cerevisiae contains high affinity permeases for Cu(I) and Fe(II). A low affinity Fe(II) permease has also been identified, designated Fet4p. A corresponding low affinity copper permease has not been characterized, although yeast cells that lack high affinity copper uptake do accumulate this metal ion. We demonstrate in the present study that Fet4p can function as a low affinity copper permease. Copper is a non-competitive inhibitor of (55)Fe uptake through Fet4p (K(i)=22 microM). Fet4p-dependent (67)Cu uptake was kinetically characterized, with K(m) and V(max) values of 35 microM and 8 pmol of copper/min per 10(6) cells respectively. A fet4-containing strain exhibited no saturable, low affinity copper uptake indicating that this uptake was attributable to Fet4p. Mutant forms of Fet4p that exhibited decreased efficiency in (55/59)Fe uptake were similarly compromised in (67)Cu uptake, indicating that similar amino acid residues in Fet4p contribute to both uptake processes. The copper taken into the cell by Fet4p was metabolized similarly to the copper taken into the cell by the high affinity permease, Ctr1p. This was shown by the Fet4p-dependence of copper activation of Fet3p, the copper oxidase that supports high affinity iron uptake in yeast. Also, copper-transported by Fet4p down-regulated the copper sensitive transcription factor, Mac1p. Whether supplied by Ctr1p or by Fet4p, an intracellular copper concentration of approx. 10 microM caused a 50% reduction in the transcriptional activity of Mac1p. The data suggest that the initial trafficking of newly arrived copper in the yeast cell is independent of the copper uptake pathway involved, and that this copper may be targeted first to a presumably small 'holding' pool prior to its partitioning within the cell.
Hassett
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Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY 14214, USA.
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Kosman
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D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D027682:Cation Transport Proteins; D003300:Copper / Q000378:metabolism*; D000079922:Copper Transport Proteins; D000079923:Copper Transporter 1; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007477:Ions; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000378:metabolism; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic
C490078:CTR1 protein, S cerevisiae; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D000079922:Copper Transport Proteins; D000079923:Copper Transporter 1; C105847:FET4 protein, S cerevisiae; D007477:Ions; D033862:Iron-Binding Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D003300:Copper; D007501:Iron; D005947:Glucose; D005690:Galactose