Mitochondria export iron-sulfur and sulfur intermediates to the cytoplasm for iron-sulfur cluster assembly and tRNA thiolation in yeast

J Biol Chem. 2019 Jun 14;294(24):9489-9502. doi: 10.1074/jbc.RA119.008600. Epub 2019 Apr 30.

Abstract

Iron-sulfur clusters are essential cofactors of proteins. In eukaryotes, iron-sulfur cluster biogenesis requires a mitochondrial iron-sulfur cluster machinery (ISC) and a cytoplasmic iron-sulfur protein assembly machinery (CIA). Here we used mitochondria and cytoplasm isolated from yeast cells, and [35S]cysteine to detect cytoplasmic Fe-35S cluster assembly on a purified apoprotein substrate. We showed that mitochondria generate an intermediate, called (Fe-S)int, needed for cytoplasmic iron-sulfur cluster assembly. The mitochondrial biosynthesis of (Fe-S)int required ISC components such as Nfs1 cysteine desulfurase, Isu1/2 scaffold, and Ssq1 chaperone. Mitochondria then exported (Fe-S)int via the Atm1 transporter in the inner membrane, and we detected (Fe-S)int in active form. When (Fe-S)int was added to cytoplasm, CIA utilized it for iron-sulfur cluster assembly without any further help from the mitochondria. We found that both iron and sulfur for cytoplasmic iron-sulfur cluster assembly originate from the mitochondria, revealing a surprising and novel mitochondrial role. Mitochondrial (Fe-S)int export was most efficient in the presence of cytoplasm containing an apoprotein substrate, suggesting that mitochondria respond to the cytoplasmic demand for iron-sulfur cluster synthesis. Of note, the (Fe-S)int is distinct from the sulfur intermediate called Sint, which is also made and exported by mitochondria but is instead used for cytoplasmic tRNA thiolation. In summary, our findings establish a direct and vital role of mitochondria in cytoplasmic iron-sulfur cluster assembly in yeast cells.

Keywords: ABC transporter; cytoplasm; export; iron; iron–sulfur protein; metal cofactor; mitochondria; sulfur; tRNA thiolation; yeast.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Biological Transport
  • Cytoplasm / metabolism*
  • Iron / metabolism*
  • Iron-Sulfur Proteins / metabolism*
  • Mitochondrial Proteins / metabolism*
  • RNA, Fungal / metabolism*
  • RNA, Transfer / metabolism*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Sulfhydryl Compounds / metabolism
  • Sulfur / metabolism*

Substances

  • Iron-Sulfur Proteins
  • Mitochondrial Proteins
  • RNA, Fungal
  • Saccharomyces cerevisiae Proteins
  • Sulfhydryl Compounds
  • Sulfur
  • RNA, Transfer
  • Iron