title: An engineered bifunctional high affinity iron uptake protein in the yeast plasma membrane.
abstract: High affinity iron uptake in fungi is supported by a plasma membrane protein complex that includes a multicopper ferroxidase enzyme and a ferric iron permease. In Saccharomyces cerevisiae, this complex is composed of the ferroxidase Fet3p and the permease Ftr1p. Fe(II) serves as substrate for Fe-uptake by being substrate for Fet3p; the resulting Fet3p-produced Fe(III) is then transported across the membrane via Ftr1p. A model of metabolite channeling of this Fe(III) is tested here by first constructing and kinetically characterizing in Fe-uptake two Fet3p-Ftr1p chimeras in which the multicopper oxidase/ferroxidase domain of Fet3p has been fused to the Ftr1p iron permease. Although the bifunctional chimeras are as kinetically efficient in Fe-uptake as is the wild type two-component system, they lack the adaptability and fidelity in Fe-uptake of the wild type. Specifically, Fe-uptake through the Fet3p, Ftr1p complex is insensitive to a potential Fe(III) trapping agent - citrate - whereas Fe-uptake via the chimeric proteins is competitively inhibited by this Fe(III) chelator. This inhibition does not appear to be due to scavenging Fet3p-produced Fe(III) that is in equilibrium with bulk solvent but could be due to leakiness to citrate found in the bifunctional but not the two-component system. The data are consistent with a channeling model of Fe-trafficking in the Fet3p, Ftr1p complex and suggest that in this system, Fet3p serves as a redox sieve that presents Fe(III) specifically for permeation through Ftr1p.
authors.affiliation: Department of Biochemistry, The University at Buffalo, 140 Farber Hall, Buffalo, NY 14214, USA.
authors.forename: E Y
authors.initials: EY
authors.lastname: Kwok
authors.forename: C S
authors.initials: CS
authors.lastname: Stoj
authors.forename: S
authors.initials: S
authors.lastname: Severance
authors.forename: D J
authors.initials: DJ
authors.lastname: Kosman
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D010084:Oxidation-Reduction; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D007501:Iron