Biochemical Journal

Research article

The Fe(II) permease Fet4p functions as a low affinity copper transporter and supports normal copper trafficking in Saccharomyces cerevisiae

Richard HASSETT, David R. DIX, David J. EIDE, Daniel J. KOSMAN


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 55Fe uptake through Fet4p (Ki = 22µM). Fet4p-dependent 67Cu uptake was kinetically characterized, with Km and Vmax values of 35µM and 8pmol of copper/min per 106 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 55/59Fe uptake were similarly compromised in 67Cu 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µM 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.

  • copper uptake
  • copper trafficking
  • metal interactions
  • yeast.