A Specific Role of the Yeast Mitochondrial Carriers Mrs3/4p in Mitochondrial Iron Acquisition under Iron-limiting Conditions

Thomas Eickhorst,Andreas Seubert,Rudolf J Schweyen,Nadine Richhardt,Jochen A Stadler,Roland Lill,Gerlinde Wiesenberger,Ulrich Mühlenhoff

doi:10.1074/jbc.m307847200

Thomas Eickhorst, Andreas Seubert + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m307847200

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Abstract

The yeast genes MRS3 and MRS4 encode two members of the mitochondrial carrier family with high sequence similarity. To elucidate their function we utilized genome-wide expression profiling and found that both deletion and overexpression of MRS3/4 lead to up-regulation of several genes of the "iron regulon." We therefore analyzed the two major iron-utilizing processes, heme formation and Fe/S protein biosynthesis in vivo, in organello (intact mitochondria), and in vitro (mitochondrial extracts). Radiolabeling of yeast cells with 55Fe revealed a clear correlation between MRS3/4 expression levels and the efficiency of these biosynthetic reactions indicating a role of the carriers in utilization and/or transport of iron in vivo. Similar effects on both heme formation and Fe/S protein biosynthesis were seen in organello using mitochondria isolated from cells grown under iron-limiting conditions. The correlation between MRS3/4 expression levels and the efficiency of the two iron-utilizing processes was lost upon detergent lysis of mitochondria. As no significant changes in the mitochondrial membrane potential were observed upon overexpression or deletion of MRS3/4, our results suggest that Mrs3/4p carriers are directly involved in mitochondrial iron uptake. Mrs3/4p function in mitochondrial iron transport becomes evident under iron-limiting conditions only, indicating that the two carriers do not represent the sole system for mitochondrial iron acquisition.

Highlights

The yeast genes MRS3 and MRS4 encode two members of the mitochondrial carrier family with high sequence similarity
Another hint toward the function of Mrs3/4p comes from previous work by Foury and Roganti [25] showing that (i) deletion of MRS3/4 in a frataxin deletion mutant (⌬yfh1 cells) is able to suppress mitochondrial iron accumulation, (ii) overexpression of MRS4 in ⌬yfh1 cells leads to higher mitochondrial iron load, and (iii) overexpression of MRS4 in wild-type cells results in increased heme formation, pointing to a role of these carriers in mitochondrial iron homeostasis
Genes down-regulated in ⌬mrs3/4 cells include LEU1 and GLT1 coding for Fe/S proteins (Table I)

Summary

Introduction

The yeast genes MRS3 and MRS4 encode two members of the mitochondrial carrier family with high sequence similarity To elucidate their function we utilized genome-wide expression profiling and found that both deletion and overexpression of MRS3/4 lead to up-regulation of several genes of the “iron regulon.”. Radiolabeling of yeast cells with 55Fe revealed a clear correlation between MRS3/4 expression levels and the efficiency of these biosynthetic reactions indicating a role of the carriers in utilization and/or transport of iron in vivo. Similar effects on both heme formation and Fe/S protein biosynthesis were seen in organello using mitochondria isolated from cells grown under iron-limiting conditions. Another hint toward the function of Mrs3/4p comes from previous work by Foury and Roganti [25] showing that (i) deletion of MRS3/4 in a frataxin deletion mutant (⌬yfh cells) is able to suppress mitochondrial iron accumulation, (ii) overexpression of MRS4 in ⌬yfh cells leads to higher mitochondrial iron load, and (iii) overexpression of MRS4 in wild-type cells results in increased heme formation, pointing to a role of these carriers in mitochondrial iron homeostasis

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