Cloning of Pichia pastoris Fet3: Insights into the high affinity iron uptake system

High-affinity iron uptake by yeast cells appears to require the presence of a complex formed on the plasma membrane by the multicopper oxidase Fet3 an d the permease Ftr1 which work together to allow iron to enter safely insid e the cell. The Pichia pastoris ferroxidase Fet3 has been cloned and it has been found to display high sequence similarity to other yeast multicopper oxidases, including all the predicted ligands for the catalytic copper atom s and for the iron substrate. P. pastoris appears to possess a high-affinit y iron uptake system similar to that of S. cerevisiae, as far as regulation of expression is concerned. However, the P. pastoris high-affinity iron up take system presents a K-m value for iron almost ten times higher than that of S. cerevisiae, possibly to control iron fluxes over a wider range of co ncentrations of this metal, in order to avoid toxic iron overloading. (C) 2 001 Academic Press.