Ferrichrome induces endosome to plasma membrane cycling of the ferrichrome transporter, Arn1p, in Saccharomyces cerevisiae

Abstract

Siderophores are small iron-binding molecules that are synthesized and secreted in the iron-free form by microorganisms. Saccharomyces cerevisiae takes up iron bound to siderophores by two separate systems, one of which requires the ARN family of sidero phore-iron transporters. Arn1p and Arn3p are expressed in endosome-like intracellular vesicles. Here we present evidence that, in the absence of its specific substrate, ferrichrome, Arn1p is sorted directly from the Golgi to the endosomal compartment and does not cycle to the plasma membrane. When cells are exposed to ferrichrome at low concentrations, Arn1p stably relocalizes to the plasma membrane. At higher concentrations of ferrichrome, Arn1p relocalizes to the plasma membrane and rapidly undergoes endocytosis. Plasma membrane localization of Arn1p occurs only in the presence of its specific substrate, and not in the presence of other siderophores. Despite expression of Arn1p on the plasma membrane, mutant strains with defects in endocytosis exhibit reduced uptake of ferrichrome-iron. Thus, siderophores influence the trafficking of the Arn transporters within the cell and this trafficking is important for transporter function.

Genome-Wide Screen for Genes With Effects on Distinct Iron Uptake Activities in Saccharomyces cerevisiae

“…The presence of siderophores in the medium has to be "sensed" by the cells prior to the defects in either oxidase separately. BUD32, PKR1, and RAV1 knockouts also showed similar phenotypes to the siderophore receptors being exported at the plasma membrane (Kim et al 2002). Transcription of genes for copper trafficking mutants, with low-ferrous uptake partly compensated by copper addition to the media these receptors is itself subject to complex regulation, depending on Aft1/2 and Tup1/Cyc8 (Lesuisse et al and constitutively high-FOB uptake (node 5A-2).…”

“…⌬arf1, etc.) with impaired endosome fusion with late endosome and vacuolar compartments are expected to Many genes of these first two nodes (5B-1, 5B-2) are involved in transcriptional regulation and RNA proexhibit decreased recycling of Sit1 (Kim et al 2002). Increased Sit1 at the cell surface in these mutants could cessing (LSM1,LSM6,LSM7,PAT1,SSN3,CYC8,SSN8,MED1,etc.).…”

Siderophore-Based Iron Acquisition and Pathogen Control

“…Two ferrichrome binding sites were predicted in Arn1p, one with a higher affinity (K D of 8.1 nM) and one with a lower affinity (K D of 1.2 M). Although the half-maximal saturation of ferrichrome-delivered iron uptake by Arn1p is similar to the K D of the lower-affinity binding site, which might speak for predominantly low-affinity binding of ferrichrome to Arn1p if substrate binding rather than translocation is supposed as the rate-limiting uptake step (223), high-affinity binding was suggested to occur under normal in vivo conditions since it was observed that under nonoverexpression conditions, Arn1p localizes to the plasma membrane already in the presence of low nanomolar concentrations of ferrichrome but not in the absence of substrate that leads to the sorting of Arn1p to the endosomal compartment (166). Further transport studies revealed a high stereoselectivity of fungal Fe-siderophore uptake systems, as shown in Rhodotorula pilimanae, which preferred ⌬ rhodotorulic acid (226).…”

Structural Requirements for the Activity of the MirB Ferrisiderophore Transporter of Aspergillus fumigatus

“…In S. cerevisiae, one model holds that transporters for enterobactin and TAFC are not located in the plasma membrane at all times; instead, they are kept in endosome-like vesicles near the plasma membrane and are localized to the plasma membrane when cells are exposed to siderophores (37). Furthermore, it is believed that siderophores in S. cerevisiae are not simply transported across the plasma membrane but instead are taken up by endocytosis of the transporter after it binds to its specific siderophores (37). Once in the endosome, the transporter would shuttle the siderophore-iron complex across the endosomal membrane to the cytosol.…”